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TABLE OF CONTENTS
EXECUTIVE SUMMARY ........................................................................................................................II
1
2
INTRODUCTION ............................................................................................................................. 1
1.1
Background .............................................................................................................................. 1
1.2
Contract Data and Management ..............................................................................................2
1.3
Scope of Services and Objectives ........................................................................................... 2
1.4
Project Description ................................................................................................................... 3
REVIEW OF PREVIOUS STUDIES ................................................................................................6
2.1
Route Assessement ................................................................................................................. 6
2.1.1
3
TOPOGRAPHICAL SURVEY .......................................................................................................16
3.1
Introduction .............................................................................................................................16
3.2
Mobilization of Surveyors and Equipment’s .......................................................................... 16
3.3
Data Collection ....................................................................................................................... 17
3.4
Scope of Topographic Survey ............................................................................................... 17
3.5
GPS Surveying Methodology .................................................................................................18
3.5.1
Establishment of Geodetic Control Points Using Global Positioning System (GPS) .... 18
3.5.2
Tying with National Coordinate System ......................................................................... 18
3.5.3
Coordinate System ......................................................................................................... 18
3.5.4
Verification of Positioning ............................................................................................... 18
3.5.5
Data Processing and Mapping ....................................................................................... 18
3.6
4
Route Identification ........................................................................................................... 6
Benchmark Setup ...................................................................................................................19
3.6.1
Control Traverse-Line ..................................................................................................... 19
3.6.2
Geometric Level-Line ......................................................................................................20
3.7
Collection of Cross-section Data ........................................................................................... 20
3.8
Data Processing and CADD .................................................................................................. 21
HYDROLOGICAL AND HYDRAULIC STUDY ............................................................................ 22
4.1
Project Description ................................................................................................................. 22
4.2
Methodology and Standards .................................................................................................. 23
4.2.1
General ........................................................................................................................... 23
4.2.2
Methodology ................................................................................................................... 23
4.2.3
Design Standards /Frequency ........................................................................................ 24
4.2.4
Methods of Design Flood Computation ..........................................................................25
4.3
Data Collection and Analysis ................................................................................................. 26
4.3.1
4.4
Data Collection ................................................................................................................27
Previous Studies, Existing Data and Maps ........................................................................... 27
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4.4.1
Data and documents .......................................................................................................27
4.4.2
Existing Conditions ......................................................................................................... 28
4.4.3
Hydro-Climatic Data ........................................................................................................29
4.4.4
Climate ............................................................................................................................ 29
4.4.5
Rainfall Data ................................................................................................................... 30
4.4.6
Frequency Analysis ........................................................................................................ 31
4.4.7
Catchment area Delineation ........................................................................................... 32
4.4.8
Hydrologic Soil Type .......................................................................................................33
4.4.9
Vegetation and Land Use ............................................................................................... 34
4.5
Hydrological Study ................................................................................................................. 35
4.5.1
General ........................................................................................................................... 35
4.5.2
Methods of Peak Flood Computations ........................................................................... 36
4.5.3
Rational Method ..............................................................................................................36
4.5.4
SCS Unit Hydrograph Method ........................................................................................ 40
4.6
Hydraulic Design .................................................................................................................... 47
4.6.1
General ........................................................................................................................... 47
4.6.2
Hydraulic Design Standard .............................................................................................47
4.6.3
Manning’s Formula of Hydraulic Analysis ...................................................................... 48
4.6.4
Culvert and Auxiliary Facility Hydraulic Design ..............................................................48
4.6.5
Pipe Culverts ...................................................................................................................49
4.6.6
Slab/box Culverts ............................................................................................................50
4.6.7
Design of Major Cross Drainage Structures ...................................................................52
4.6.8
Design of Longitudinal Drainage Facility ........................................................................54
4.6.9
Bridge Scouring .............................................................................................................. 56
4.6.10
Back water effect (Afflux) ................................................................................................57
4.7
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Conclusions and recommendations ...................................................................................... 58
GEOMETRIC DESIGN ..................................................................................................................59
5.1
Introduction .............................................................................................................................59
5.2
Design Control and Criteria ....................................................................................................62
5.2.1
Functional Classification .................................................................................................62
5.2.2
Geometric Classification ................................................................................................. 63
5.2.3
Traffic Volume and Characteristics ................................................................................ 64
5.2.4
Terrain Classification ...................................................................................................... 71
5.2.5
Type of area Classification ............................................................................................. 73
5.2.6
ERA Design Standards ...................................................................................................73
5.2.7
Selection of Design Standard Parameters and Their Limiting Values ...........................77
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5.3
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Geometrical Design of the Project Road ............................................................................... 80
5.3.1
General ........................................................................................................................... 80
5.3.2
Analysis Horizontal Alignment Design ........................................................................... 80
5.3.3
Vertical Alignment ...........................................................................................................86
5.3.4
Draft Engineering Design Drawings ............................................................................... 93
5.4
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Requested Departures from Standard ...................................................................................93
5.4.1
General ........................................................................................................................... 93
5.4.2
List of Requested Departures from Standard ................................................................ 95
5.4.3
Reasons and Justifications for the Requested Departures from Standard ................... 99
5.4.4
Mitigation Measures ......................................................................................................103
5.4.5
Conclusion and Recommendations ..............................................................................104
ROAD SAFETY DESIGN ............................................................................................................105
6.1
Review of Existing Accident Data ........................................................................................ 105
6.2
Road Safety ..........................................................................................................................110
6.3
Road side Furniture and Road Markings .............................................................................111
PAVEMENT DESIGN ..................................................................................................................114
7.1
Introduction ...........................................................................................................................114
7.2
Design Standards and Departure ........................................................................................ 114
7.2.1
Design Standards ......................................................................................................... 114
7.2.2
Design Period ............................................................................................................... 114
7.3
Existing Pavement Condition Survey .................................................................................. 115
7.4
Traffic Volume ...................................................................................................................... 115
7.4.1
General ......................................................................................................................... 115
7.4.2
Traffic Survey ................................................................................................................115
7.4.3
Traffic Survey Stations ................................................................................................. 116
7.4.4
Vehicle Classification ....................................................................................................117
7.4.5
Traffic Count and Analysis ............................................................................................117
7.4.6
Generated Traffic ..........................................................................................................135
7.4.7
Traffic Growth and Forecast ......................................................................................... 139
7.4.8
Traffic Loading .............................................................................................................. 149
7.5
Subgrade Soil Investigation. ................................................................................................ 158
7.5.1
General ......................................................................................................................... 158
7.5.2
Soil Extension Survey ...................................................................................................158
7.5.3
Sampling and Logging ..................................................................................................159
7.5.4
Subgrade Soil Analysis. ................................................................................................160
7.5.5
Subgrade Soil Data Interpretation ................................................................................ 165
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7.5.6
7.6
Unsuitable soil sections ................................................................................................ 166
Pavement Design .................................................................................................................169
7.6.1
Pavement Design Using ERA’s Pavement Design Manual. ........................................169
7.6.2
Design of Shoulder ....................................................................................................... 174
7.7
Design for Geo-Hazards ...................................................................................................... 177
7.7.1
Weak Subgrade Soil Sections ......................................................................................177
7.7.2
Treatment of Weak subgrade and/or expansive clay soils .......................................... 180
7.7.3
Treatment method for weak subgrade sections: ..........................................................180
7.7.4
Treatment method for expansive clay soil sections: .................................................... 180
7.7.5
Erodible Soil Sections ...................................................................................................181
7.7.6
Treatment method for erodible soils .............................................................................181
7.7.7
Swampy or Water Logged Sections ............................................................................. 182
7.7.8
Treatment of Swampy Sections ................................................................................... 182
7.8
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Construction Material Investigation. .................................................................................... 182
7.8.1
General ......................................................................................................................... 182
7.8.2
Rock Sources for Surfacing, Base, Concrete and Masonry Works .............................183
7.8.3
Natural Gravel for Subbase, Capping Layer and Embankment .................................. 185
7.8.4
Natural Sand Sources /Fine Aggregate ....................................................................... 187
7.8.5
Water Sources for Construction ................................................................................... 187
GEOTECHNICAL DESIGN .........................................................................................................188
8.1
Geological Setting ................................................................................................................ 188
8.1.1
Geological Setting of the Project Area ......................................................................... 188
8.1.2
Local Road Corridor Geological Settings ..................................................................... 189
8.2
Seismic Setting and Earthquake Hazards ...........................................................................190
8.3
Site Reconnaissance for Slope Stability ..............................................................................191
8.4
Problematic Sub-Grade Soil Sections ................................................................................. 191
8.4.1
Expansive and/or Weak subgrade sections .................................................................191
8.5
Near Surface Ground water/ Swampy Section ....................................................................194
8.6
Erodible Soil ......................................................................................................................... 194
8.7
Design of Embankments, Cuttings and Retaining Structures ............................................. 195
8.7.1
Design of Embankments .............................................................................................. 195
8.7.2
Design of Cuttings ........................................................................................................ 198
8.7.3
Safe Angle of Cut Slope and Berms ............................................................................ 199
8.7.4
Recommended Back Slopes for the Project Alignment ............................................... 200
8.7.5
Method of Rock Excavation ..........................................................................................202
8.7.6
Design of Retaining Structures .....................................................................................203
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8.7.7
8.8
Drainage Controls .........................................................................................................205
Bridge Foundation Investigation .......................................................................................... 205
8.8.1
General ......................................................................................................................... 205
8.8.2
Field Investigation .........................................................................................................206
8.9
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Conclusion ............................................................................................................................214
STRUCTURAL DESIGN ............................................................................................................. 215
9.1
General .................................................................................................................................215
9.2
Structures Design Standard .................................................................................................215
9.2.1
Methodology ................................................................................................................. 215
9.2.2
Loading ......................................................................................................................... 215
9.3
Permanent Loads .................................................................................................................216
9.4
Transient loads .....................................................................................................................216
9.5
Environmental Effects .......................................................................................................... 217
9.5.1
Materials ....................................................................................................................... 219
9.6
Structure Type Selection ......................................................................................................220
9.7
Structural Evaluation of Existing Structures ........................................................................ 221
9.7.1
9.8
Major and Minor Drainage Structures .......................................................................... 221
Detail Design ........................................................................................................................ 223
9.8.1
Bridges .......................................................................................................................... 223
9.8.2
Culverts ......................................................................................................................... 223
9.9
Structures in the Project .......................................................................................................224
9.9.1
Major Structures ........................................................................................................... 224
9.9.2
Minor Structures ........................................................................................................... 225
10
UTILITIES AND PRIVATE ACCESSES ................................................................................. 226
10.1
Utilities ..................................................................................................................................226
10.2
Private Accesses ..................................................................................................................226
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ANNEXES
Appendix 1. Hydrology & Hydraulics Analysis
Appendix 2. List of horizontal and vertical alignment data
Appendix 3. Typical Cross-Section
Appendix 4. General Plan and Elevation Drawings
Appendix 5. Masonry Abutment and Wing-wall Design
Appendix 6. Statistical Calculation of Bridges
Appendix 7. Construction materials location
Appendix 8. Laboratory test results
Appendix 9. Traffic Analysis
LIST OF TABLES
Table 1- 1: Contract Data ........................................................................................................................2
Table 1- 2: Project Description ................................................................................................................3
Table 1- 3: Project Control Points ...........................................................................................................3
Table 2- 1: Road segments of the project .............................................................................................. 6
Table 2- 2: Road segment class ............................................................................................................. 6
Table 3- 1: List of Survey instruments .................................................................................................. 16
Table 3- 2: List personnel’s (team 1: GPS team) ................................................................................. 17
Table 3- 3: List personnel’s (team 2: Control traverse survey& Topographic Survey) ........................ 17
Table 4- 1:: Return Periods Considered (ERA Drainage Design Manual 2013) ................................. 25
Table 4- 2: Flood estimation methods (Table 5-3 of ERA DDM). ........................................................ 25
Table 4- 3: Physiographic and climate data ......................................................................................... 28
Table 4- 4: Monthly Highest Rainfall Data ............................................................................................ 30
Table 4- 5: 24hr Rainfall Depth Vs Frequency ..................................................................................... 31
Table 4- 6: Derived Run-off Coefficients (C) ........................................................................................ 37
Table 4- 7: Run-off Coefficient (C) as per ERA Drainage Design Manual 2002) ................................ 37
Table 4- 8: Frequency factor, Cf ........................................................................................................... 37
Table 4- 9: Roughness Coefficients (Manning’s n) for Sheet Flow ......................................................39
Table 4- 10: Coefficients for SCS Peak Discharge Method ................................................................. 43
Table 4- 11: Input of hydraulic data for HY8 from Hundi Gudina Scl Nejebac Kidane Mihret @km
2+060 .................................................................................................................................................... 50
Table 4- 12: Free board recommendation as per ERA DDM ...............................................................52
Table 4- 13: Roughness coefficients and Maximum permissible velocity ........................................... 55
Table 5- 1: Road segment class and road width .................................................................................. 62
Table 5- 2: Road functional Classification verses Design Period ........................................................ 65
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Table 5- 3: Traffic forecast of road segment 6 and 7 at station 1 for the years 2028– 2047 ............. 65
Table 5- 4: Traffic forecast of road segment 2 at station 2 for the years 2028– 2047 ........................66
Table 5- 5: Traffic forecast of road segment 3 at station 2 for the years 2028– 2047 ........................67
Table 5- 6: Traffic forecast of road segment 1-1 at station 2 for the years 2028– 2047 .................... 68
Table 5- 7: Traffic forecast of road segment 1-2 at station 2 for the years 2028– 2047 .................... 68
Table 5- 8: Traffic forecast of road segment 5 at station 3 for the years 2028– 2047 ........................69
Table 5- 9: Traffic forecast of road segment 4, 8 and 9 at station 4 for the years 2028– 2047 ......... 70
Table 5- 10: Design Standard for sections of the Project Road ..........................................................71
Table 5- 11: Terrain Classification of the Road Project ........................................................................72
Table 5- 12: Percentage distribution of terrain ..................................................................................... 73
Table 5- 13: Design vehicle physical characteristics ............................................................................75
Table 5- 14: Design Vehicle ..................................................................................................................75
Table 5- 15: Design Vehicle for each road class ..................................................................................76
Table 5- 16: Design Standards ............................................................................................................. 78
Table 5- 17: Slope Ratio Table – Vertical to Horizontal ....................................................................... 80
Table 5- 18: Road segment of the project road ....................................................................................81
Table 5- 19: Road segment by percentage curve lengths .................................................................. 81
Table 5- 20: Comparison of sections by speed distribution relative to the overall length of the curve82
Table 5- 21: Built up areas ....................................................................................................................85
Table 5- 22: Summary of Vertical Alignment Analysis Road segment -1 ............................................ 86
Table 5- 23: Summary of Vertical Alignment Analysis Road segment -2 ............................................ 87
Table 5- 24: Summary of Vertical Alignment Analysis Road segment -3 ............................................ 87
Table 5- 25: Summary of Vertical Alignment Analysis Road segment -4 ............................................ 87
Table 5- 26: Summary of Vertical Alignment Analysis Road segment -5 ............................................ 88
Table 5- 27: Summary of Vertical Alignment Analysis Road segment -6 ............................................ 88
Table 5- 28: Summary of Vertical Alignment Analysis Road segment -7 ............................................ 88
Table 5- 29: Summary of Vertical Alignment Analysis Road segment -8 ............................................ 89
Table 5- 30: Summary of Vertical Alignment Analysis Road segment -9 ............................................ 89
Table 5- 31: Summary of Vertical Alignment Analysis Road segment -10 .......................................... 89
Table 5- 32: Departure from Minimum Horizontal Curve Radii for Road segment-1 ...........................95
Table 5- 33: Departure from Minimum Horizontal Curve Radii for Road segment-6 ...........................96
Table 5- 34: Departure from Maximum Grade for Road segment -1 ................................................... 97
Table 5- 35: Departure from Maximum Grade for Road segment -2 ................................................... 98
Table 5- 36: Departure from Maximum Grade for Road segment -2 ................................................... 98
Table 6- 1: Motor vehicle accidents in Ethiopia, 2003/04 - 2007/08 .................................................. 105
Table 6- 2: Severity of traffic accidents in Ethiopia ............................................................................ 106
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Table 6- 3: Crashes by Driver Age, Education, and Gender, July 2005-June 2011 ..........................107
Table 6- 4: Road Traffic Fatality Crashes by Road Type and Road Pavement July 2005-June 2011
............................................................................................................................................................ 107
Table 6- 5: Fatal and Injury Crashes in the Six Year Period by Lanes/Medians, Road Alignment,
Junction Type and Illumination Conditions ........................................................................................ 108
Table 6- 6: Crashes by Land Use ....................................................................................................... 109
Table 6- 7: Guide post Spacing .......................................................................................................... 112
Table 7- 1: Traffic Survey Stations, Road Section, Duration and Purpose of the Count ...................116
Table 7- 2: Vehicle Classification ........................................................................................................117
Table 7- 3: Day Time Traffic Count Survey Result: Station 1 ............................................................ 118
Table 7- 4: Day Time Traffic Count Survey Result: Station 2 ............................................................ 118
Table 7- 5: Day Time Traffic Count Survey Result: Station 3 ............................................................ 119
Table 7- 6: Day Time Traffic Count Survey Result: Station 4 ............................................................ 119
Table 7- 7: Night Time Traffic Count Survey Result: Station 1 .......................................................... 120
Table 7- 8: Night Time Traffic Count Survey Result: Station 2 .......................................................... 120
Table 7- 9: Night Time Traffic Count Survey Result: Station 3 .......................................................... 120
Table 7- 10: Night Time Traffic Count Survey Result: Station 4 ........................................................ 120
Table 7- 11: Night Factor: Station 1 ....................................................................................................121
Table 7- 12: Night Factor: Station 2 ....................................................................................................121
Table 7- 13: Night Factor: Station 3 ....................................................................................................122
Table 7- 14: Night Factor: Station 4 ....................................................................................................123
Table 7- 15: Motorized Average Daily Traffic (ADT): Station 1 ..........................................................123
Table 7- 16: Motorized Average Daily Traffic (ADT): Station 2 ..........................................................124
Table 7- 17: Motorized Average Daily Traffic (ADT): Station 3 ..........................................................124
Table 7- 18: Motorized Average Daily Traffic (ADT): Station 4 ..........................................................124
Table 7- 19: Day Time Non-motorized Traffic survey result: Station 1 .............................................. 125
Table 7- 20: Day Time Non-motorized Traffic survey result: Station 2 .............................................. 125
Table 7- 21: Day Time Non-motorized Traffic survey result: Station 3 .............................................. 126
Table 7- 22: Day Time Non-motorized Traffic survey result: Station 4 .............................................. 126
Table 7- 23: Night Time Non-motorized Traffic survey result: Station 1 ............................................126
Table 7- 24: Night Time Non-motorized Traffic survey result: Station 2 ............................................127
Table 7- 25: Night Time Non-motorized Traffic survey result: Station 3 ............................................127
Table 7- 26: Night Time Non-motorized Traffic survey result: Station 4 ............................................127
Table 7- 27: Night Factor: @ station 1 ................................................................................................127
Table 7- 28: Night Factor: @ station 2 ................................................................................................128
Table 7- 29: Night Factor: @ station 3 ................................................................................................128
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Table 7- 30: Night Factor: @ station 4 ................................................................................................129
Table 7- 31: Non-Motorized Average Daily Traffic (ADT)-Station 1 ...................................................130
Table 7- 32: Non-Motorized Average Daily Traffic (ADT)-Station 2 ...................................................130
Table 7- 33: Non-Motorized Average Daily Traffic (ADT)-Station 3 ...................................................130
Table 7- 34: Non-Motorized Average Daily Traffic (ADT)-Station 4 ...................................................130
Table 7- 35: Modal shift Traffic ........................................................................................................... 131
Table 7- 36: Summary of Normal Traffic – Station 1 ..........................................................................132
Table 7- 37: Summary of Normal Traffic – Station 2 ..........................................................................132
Table 7- 38: Summary of Normal Traffic – Station 3 ..........................................................................132
Table 7- 39: Summary of Normal Traffic – Station 4 ..........................................................................133
Table 7- 40: Potential Distributed Traffic to the project roads assumptions ...................................... 133
Table 7- 41: Potential Distributed Traffic to the project roads from Station 2 (Wereda Administration)
Road segment 2 ................................................................................................................................. 134
Table 7- 42: Potential Distributed Traffic to the project roads from Station 2 (Wereda Administration)
Road segment 3 ................................................................................................................................. 134
Table 7- 43: Potential Distributed Traffic to the project roads from Station 2 (Wereda Administration)
Road segment 1-1 .............................................................................................................................. 134
Table 7- 44: Potential Distributed Traffic to the project roads from Station 2 (Wereda Administration)
Road segment 1-2 .............................................................................................................................. 134
Table 7- 45: Potential Distributed Traffic to the project roads from Station 4 (Agape Hotel) Road
segment 1-1 ........................................................................................................................................ 135
Table 7- 46: Potential Distributed Traffic to the project roads from Station 3(Main trunk road) ........ 135
Table 7- 47: Travel time to estimate Generated Traffic Factor .......................................................... 136
Table 7- 48: Station 4-Estimate of Generated Traffic Factors from the travel time ........................... 136
Table 7- 49: Station 1-Potential Generated Traffic for Project Road (taking medium scenario) ....... 137
Table 7- 50: Seasonal Conversion Factor .......................................................................................... 138
Table 7- 51: AADT of the Normal Traffic at 2023–Station 1 .............................................................. 139
Table 7- 52: AADT of the Normal Traffic at 2023–Station 4 .............................................................. 139
Table 7- 53: Schedule for Implementation of the Project ................................................................... 140
Table 7- 54: Base year Traffic (at 2028) - AADT1 – Station 1(Road segment 6&7) ......................... 140
Table 7- 55: Base year Traffic (at 2028) - AADT1 – Station 2 (Road segment 2) .............................140
Table 7- 56: Base year Traffic (at 2028) - AADT1 – Station 2 (Road segment 3) .............................141
Table 7- 57: Base year Traffic (at 2028) - AADT1 – Station 2 (Road segment 1-1) ..........................141
Table 7- 58: Base year Traffic (at 2028) - AADT1 – Station 2 (Road segment 1-2) ..........................141
Table 7- 59: Base year Traffic (at 2028) - AADT1 – Station 3 Road segment 5 ............................... 142
Table 7- 60: Base year Traffic (at 2028) - AADT1 – Station 4 (Road segment 4,8 & 9) ................... 142
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Table 7- 61: Traffic forecast of road segment 6 and 7 at station 1 for the years 2028– 2047 ......... 143
Table 7- 62: Traffic forecast of road segment 2 at station 2 for the years 2028– 2047 ....................143
Table 7- 63: Traffic forecast of road segment 3 at station 2 for the years 2028– 2047 ....................144
Table 7- 64: Traffic forecast of road segment 1-1 at station 2 for the years 2028– 2047 ................ 145
Table 7- 65: Traffic forecast of road segment 1-2 at station 2 for the years 2028– 2047 ................ 146
Table 7- 66: Traffic forecast of road segment 5 at station 3 for the years 2028– 2047 ....................146
Table 7- 67: Traffic forecast of road segment 4, 8 and 9 at station 4 for the years 2028– 2047 ..... 147
Table 7- 68: Design Standard for sections of the Project Road .........................................................148
Table 7- 69: Equivalency Factors, ESA/Vehicle Type ........................................................................150
Table 7- 70: CESA for Road segment 6 and Road segment 7 at Station 1 ..................................... 151
Table 7- 71: CESA for Road segment 2 and 10 at Station 2 ............................................................ 152
Table 7- 72: CESA for Road segment 3 at Station 2 ........................................................................ 153
Table 7- 73: CESA for Road segment 1-1 at Station 2 ..................................................................... 154
Table 7- 74: CESA for Road segment 1-2 at Station 2 ..................................................................... 155
Table 7- 75: CESA for Road segment 5 at Station 3 ........................................................................ 156
Table 7- 76: CESA for Road segment 4,8 and 9 at Station 4 ........................................................... 157
Table 7- 77: Design Traffic Classes ....................................................................................................158
Table 7- 78: Summary of the roadbed materials ................................................................................ 159
Table 7- 79: Analysis and interpretation of sub grade soil ................................................................. 165
Table 7- 80: Comparison of project rating with AASHTO rating ........................................................ 166
Table 7- 81: Unsuitable soil stretches for all Road segments of the Project ..................................... 167
Table 7- 82: Design CBR and sub grade class before and after treatment .......................................170
Table 7- 83: summery of sub grade and traffic class for the section of the road Segments. ............ 170
Table 7- 84: Pavement thickness as per ERA 2013 Flexible Pavement Design Manual Chart B1 .. 172
Table 7- 85: Pavement thickness as per ERA 2013 Flexible Pavement Design Manual Chart B1 .. 173
Table 7- 86: Shoulder Pavement thickness ........................................................................................175
Table 7- 87: Weak and/or Expansive subgrade stretches in the road segments of the project .......177
Table 7- 88: Existing gully locations along the proposed road ...........................................................181
Table 7- 89: Locations of Quary Materials Identified along the Road Segments .............................. 184
Table 7- 90: Locations of Natural Gravel Materials Identified along the Road Segments .................185
Table 7- 91: Water source On the Vicinity of Road Segments. ......................................................... 187
Table 8- 1: List of problematic subgrade sections ..............................................................................192
Table 8- 2: Erodible soil section (Formation of Gully) ........................................................................ 194
Table 8- 4: Design criteria for settlement, side slope stability and bearing capacity of embankments
............................................................................................................................................................ 195
Table 8- 5: High fill sections along the road project ........................................................................... 196
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Table 8- 6: Design Criteria for Cut Slope Stability ..............................................................................199
Table 8- 7: Slope Ratio Table – Vertical to Horizontal ....................................................................... 199
Table 8- 8: Recommended back slope ratio .......................................................................................200
Table 8- 9: Lists of Major Crossing Sites ............................................................................................206
Table 8- 10: Typical Correlation between DCP and SPT-N Values ...................................................210
Table 8- 11: Summaries of DCP test results and SPT N-values of each Bridge ...............................211
Table 8- 12: Summary of bearing capacity Obtained from DCP Test for each Bridge based on N55
............................................................................................................................................................ 213
Table 9- 1:: Drag Coefficient .............................................................................................................. 218
Table 9- 2: Lateral Drag Coefficient ...................................................................................................219
Table 9- 3: Schedule of Major Structures ........................................................................................... 224
Table 10- 1: Utilities along the project road ........................................................................................226
LIST OF FIGURES
Figure 1- 1: Location Map ....................................................................................................................... 5
Figure 2- 1: All the Project road segments of Chiro Town Internal Asphalt Road Project .....................7
Figure 2- 2: Roads from Muz Tera to TTC, Kebt Tera to Aana Ciro, Sumayewu Bridge to Addis
Ketema, Agape Hotel to Agricultural research institute then to TTC, Agricultural Research Institute to
Odaa Bultum University, Chiro town administration to Madhicho No 2 School then Madhicho No.9
(Leyila), Hundi Gudina Scl-Nejebac Kidane Mihret, Hundi Gudina Scl-Aschalew Hotel, Blood BankGende Kuteba Bono. .............................................................................................................................. 8
Figure 2- 3: Roads from Muz Tera to TTC ............................................................................................. 8
Figure 2- 4: Roads from Kebt Tera to Aana Ciro and Sumayewu Bridge to Addis Ketema ..................9
Figure 2- 5: Roads from Agape Hotel to Agricultural research institute then to TTC and Agricultural
Research Institute to Odaa Bultum University ....................................................................................... 9
Figure 2- 6: Roads from Chiro town administration to Madhicho No 2 School then Madhicho No.9
(Leyila) .................................................................................................................................................. 10
Figure 2- 7: Hundi Gudina Scl to Nejebac Kidane Mihret(S7) & Hundi Gudina Scl-Aschalew Hotel(S8)
.............................................................................................................................................................. 10
Figure 2- 8: Blood Bank to Gende Kuteba Bono(S9.1,S9.2,S9.3,S9.4,S9.5). .....................................11
Figure 4- 1: Existing Condition of Major and minor Cross Drainage Structures .................................. 29
Figure 4- 2: Climatic Zones of the Project Area ................................................................................... 30
Figure 4- 3: Mean Monthly Rainfall of Asebe Teferi ............................................................................. 31
Figure 4- 4: From NMA, IDF Curve of Asebe Teferi metrological analysis ..........................................32
Figure 4- 5: Preliminary Delineated Watershed Area ...........................................................................33
Figure 4- 6: Hydrologic Soil Group Map of the Project Area ................................................................34
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Figure 4- 7: Land use/Cover of the Road Project Area ........................................................................ 35
Figure 4- 8: Muztera Tcc @ 0+378 Delineated Watershed Area and Drainage Pattern ..................... 45
Figure 4- 9: Hydrograph for Muztera Tcc @ 0+378 ............................................................................. 45
Figure 4- 10: Kebte Tera Chiro wereda @ 1+020 Delineated Watershed Area and Drainage Pattern
.............................................................................................................................................................. 46
Figure 4- 11: Hydrograph for Kebte Tera Chiro wereda @ 1+020 .......................................................46
Figure 4- 12: Design Nomograph for the Concrete Pipe Design ......................................................... 49
Figure 4- 13: HY-8 hydraulic analysis output result along the culvert at station 2+060 ...................... 51
Figure 4- 14: HEC-RAS Output after addining Bridge waterprofile ......................................................53
Figure 5- 1: Design Vehicle template ....................................................................................................77
Figure 5- 2: Reciprocal of radii plot against the Chainages for road segment 1: (0-5+789.96) .......... 83
Figure 5- 3: Reciprocal of radii plot against the Chainages for Road segment 2: (0-1+238.25) ........ 83
Figure 5- 4: Reciprocal of radii plot against the Chainages for Road segment 3: (0-0+519.33) ........ 83
Figure 5- 5: Reciprocal of radii plot against the Chainages for Road segment 5: (0-1+237) ............. 84
Figure 5- 6: Reciprocal of radii plot against the Chainages for Road segment 6: (0-6+186) ............. 84
Figure 5- 7: Reciprocal of radii plot against the Chainages for Road segment 7: (0-2+760) ............. 84
Figure 5- 8: Reciprocal of radii plot against the Chainages for Road segment 8: (0-0+861) ............. 85
Figure 5- 9: Reciprocal of radii plot against the Chainages for Road segment 9: (0-0+817) ............. 85
Figure 5- 10: Spatial distribution of gradients for road segment 1: (0+000 – 5+789.96) ....................90
Figure 5- 11: Spatial distribution of gradients for road segment 2: (0+000 – 1+238.25) ....................91
Figure 5- 12: Spatial distribution of gradients for road segment 3: (0+000 – 0+519.33) ....................91
Figure 5- 13: Spatial distribution of gradients for road segment 4: (0+000 – 0+591.32) ....................91
Figure 5- 14: Spatial distribution of gradients for road segment 5: (0+000 – 1+237) ......................... 91
Figure 5- 15: Spatial distribution of gradients for road segment 6: (0+000 – 6+186) ......................... 92
Figure 5- 16: Spatial distribution of gradients for road segment 7: (0+000 – 2+760) ......................... 92
Figure 5- 17: Spatial distribution of gradients for road segment 8: (0+000 – 0+861) ......................... 92
Figure 5- 18: Spatial distribution of gradients for road segment 9: (0+000 – 0+817) ......................... 93
Figure 5- 19: Spatial distribution of gradients for road segment 10: (0+000 – 1+655.99) ..................93
Figure 5- 20: Illustration of the effects of using 8% maximum grade resulting in 11.2m deep cut at sta.
0+660 ( Road segment -1) ................................................................................................................. 100
Figure 5- 21: Illustration of the effects of using 9% maximum grade resulting in high fill 7.4 from sta.
2+300 to sta. 2+642 for ( Road segment -6) ......................................................................................101
Figure 5- 22: Exhibit 5.1: Fig 4.08 .......................................................................................................102
Figure 6- 1: Variation in Road Traffic Crashes By Time of Day, July 2005-June 2011 .....................106
Figure
6- 2:
Motorized
Traffic
Volume
by
Time of Day on Selected Major Road Segments in 2011 (Ethiopian Roads Authority, 2012). .......106
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Figure 6- 3: Concrete/Masonry Barrier Detail .....................................................................................113
Figure 7- 1: Summary of Soil Extension ............................................................................................. 159
Figure 7- 2: Variation of Plastic Index (PI) for the Road project .........................................................161
Figure 7- 3: Plasticity Chart for all project Road Segments Sub-grade soil .......................................162
Figure 7- 4: Percentage compositions of sub-grade soil for all Road Segments of the Project. .......162
Figure 7- 5: Variation of MDD along All road segments. ....................................................................163
Figure 7- 6: Variation of OMC along All road segments .....................................................................164
Figure 7- 7: CBR Value for all Road segments of the Project ............................................................164
Figure 7- 8: Variation of CBR-swell value for all Road segments of the Project ............................... 165
Figure 7- 9: crushed aggregate(Crusher site) and Quarry site for Base course at station 5+818 offset
0.15km RHS and 1+8 offset 1.2Km LHS with in vicinity of Road Segments ....................................185
Figure 7- 10: 4+900 Offset 0.1Km LHS Subbase existing source ..................................................... 186
Figure 7- 11: 2+600 Offset 0.14Km LHS towards, Sub base New source ........................................ 186
Figure 8- 1: Erodible soil section (gully section) .................................................................................194
Figure 8- 4: River crossing at Km 0+420 (chiro River side bank) ...................................................... 207
Figure 8- 5: River crossing at Km 5+480 (chiro River side bank) ...................................................... 207
Figure 8- 6: River crossing at Km 1+055 ............................................................................................207
Figure 8- 7: River crossing at Km 0+210 ............................................................................................208
Figure 8- 8: River crossing at Km 0+160 ............................................................................................208
Figure 8- 9: Schematic representation of DCP ...................................................................................209
Figure 8- 10: Graphic form of DCP to SPT N-30 ................................................................................211
Figure 9- 1: Designs truck ...................................................................................................................217
Figure 9- 2: Designs tandem ...............................................................................................................217
Figure 9- 3: Plan View of Pier Showing Stream Flow Pressure .........................................................219
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EXECUTIVE SUMMARY
Introduction
The Oromia Roads and Logistics Bureau (ORLB) has allocated funds towards the consultancy
services to carry out a Route Selection, Feasibility Study, Topographic Survey, and Drainage Facility
Study, Detailed Engineering Design and Tender Document preparation and Economic Evaluation for
Chiro Town Internal Asphalt Road Project. The Oromia Roads and Logistics Bureau (ORLB) invites
all eligible local Road Consultants for Consultancy Services for Topographic Survey, Drainage
Facility Study, Detailed Engineering Design, Tender Document Preparation and Economic
Evaluation of Chiro Town Internal Asphalt Road Design Project.
ORLB has been given the mandate for the construction, restoration, expansion and maintenance of
Regional road network. Its goal is to improve transport operating efficiency and reduce road
transport costs, provide access to rural, neglected and food-deficit areas and develop institutional
capacity of the sector.
Accordingly, The Oromia Roads and Logistics Bureau (ORLB) has employed Stadia Engineering
Works Consultant for the consultancy for Route Selection, Feasibility Study, Topographic Survey,
Drainage Facility Study, Detailed Engineering Design and Tender Document preparation and
Economic Evaluation for Chiro Internal Town Asphalt Road Project.
The objective of the project is to complete the road to Asphaltic concrete standard.
The objectives of the consultancy services are:
Phase I
1. Route selection and Topographic Survey
2. Feasibility Study including Preliminary Design, Environmental and Social Impact Assessment
(EIA)
Phase II
1. Detailed Engineering Design including preparation of tender Documents, Roads network
Development and
2.
Submission of Resettlement Action Plan (RAP)
The progression of the Consultancy from Phase I to Phase II will depend on the results of the
Feasibility Study, and the EIA. If the results show that the road is not viable for the proposed
construction, then Phase II shall not be undertaken. As such, each phase of the Consultancy shall
be priced separately. Authorization for the commencement of Phase II will be given by ORLB based
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on the viability of the project. It will also be based on the performance of the Consultant during
Phase I.
Hydrology and Hydraulics
Hydrology
The hydrological analysis is the most important step prior to the hydraulic design of any drainage
structure. Assessment of hydrological condition involves study of landscape characteristics of the
watershed area including topographic conditions, soil characteristics, land cover, land use and
climate conditions including atmospheric temperature and rainfall.
As the relation between the amount of precipitation on a drainage basin and the amount of runoff
from the basin is complex and too little data is available on the factors influencing the rainfall – runoff
relationship, hydrologic analysis does not bring an exact solution in peak discharge determination.
However, peak discharge generated from a given basin can be estimated reasonably by different
methods depending upon physiographic and climatic factor on the area.
The methods and step by step procedures stated in Design standard section of this report
reproduced from ERA DDM, 2013 has been used to conduct a detailed hydrological analysis of the
project.
Hydraulics
Highway hydraulic structures perform the vital function of conveying, diverting, or removing surface
water from the Highway right-of-way. Structures should be designed to be commensurate with risk,
construction cost, importance of the road, economy of maintenance, and legal requirements based
on the outlined design criteria specified at Design Standard section of this report. One type of
drainage facility will rarely provide the most satisfactory drainage for all sections of a Highway.
Bridge, major to minor culverts and open channels are the major drainage structures analyzed and
required under Chiro Town Internal Asphalt Road Project. Major defined and shallow flow
concentration sections are provided by bridges and major culverts. Open channels/ditches are also
designed and provided along the road to cutter runoff generated from road surface and adjacent
ground. Masonry U- ditch has been designed to convey and dispose runoff on town and steep grade
section with longitudinal slope exceeds 5%. Trapezoidal ditch also designed in rural sections under
mild slope configuration.
Peak discharge for different return periods has been computed and hydraulic sizing of the structures
has been made based on hydrologic and geometric inputs taking into account the site prevailing
conditions too. Recent advanced and recommended hydraulic modelling software have been
employed for side ditch, culvert and bridge designs.
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Drainage structures hydraulic evaluation and sizing has been made for stream crossings of the
proposed alignment. HY 87.12 culvert hydraulic design software’s with strong modelling capability
than spreadsheet based simplified approach have been used for culvert hydraulic evaluation and
sizing purpose. From hydrological analysis it has been realized that the runoff response
characteristics of the identified small streams is relatively moderate and brought relatively low
magnitude discharge values. Hydraulic size of the culvert by large considered site prevailing
conditions related to probable siltation and debris flow.
Bridge hydraulic modelling for identified position has been carried out using HEC RAS modelling with
strong hydraulic modelling capacity.
Design criteria limiting the potential maximum backwater rise on the immediate upstream section of
the bridge (< 0.5m), keeping the upstream bridge approach flow contraction and down stream flow
expansion stretch length a bit relaxed to avoid any impact oriented flow condition at bridge inletoutlet section has been considered in bridge hydraulic efficiency evaluation .Hydrological data from
hydrological analysis ,geometric data from ground survey work and material data from geotechnical
characterization of the rivers has been used as an analysis input.
A total of 71 drainage structures have been designed on section of the roads where all structures are
considered as Pipe, bridge and culverts (54 pipes, 12 slabs and 5 Bridges).
Geometric Design
For most road projects, economic analysis period of between 10 and 20 years from the date of
opening is considered. For the subject project a design period of 20 years from the year the road is
opened to traffic i.e. (2028 - 2047) is considered for geometric design. The project road is expected
to be opened to traffic in the year 2028.
From traffic analysis and road functional classification findings, the project road is designed to DC6
and DC7 design standard as per ERA Geometric Design Manual 2013. The consultant concludes
that the road shall be constructed to DC6 Design standard.
Pavement Design
Existing Pavement Condition
Pavement condition survey was made along the existing Chiro-Town Internal Asphalt road project.
The condition of the existing road section is assessed to check its effect on the new Asphalt surface
pavement design of the project and to determine the treatment measures required to
maintain/reconstruct the road.
During the reconnaissance site visit, visual subgrade soil extension survey was carried out to
determine the extent of the subgrade materials along the accessible sections of project route corridor.
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The project area dominant road bed material of Chiro Town Road Segments Are Dark brown silty
CLAY soil which is commonly Poor roadbed material.
Sub-grade Strength
The field investigation tasks were carried out for the Chiro Town Internal Asphalt Road project to
undertake the subgrade soils investigation, which includes the geological setting of the project area,
soil extension, sampling and logging, etc.
AASHTO soil classification reveals that the sub grade materials along all Road Segments section of
the alignments mainly classified as A-1-b, A-2-7, A-4, A-6, A-7-5 and A-7-6 soil groups. Out of the
Six Groups A-7-6 comprise 35.3% of the sub grade material (the largest proportion) which is
followed by A-7-5, 33.3% then A-2-7,25.5% and A-1-b, A-4 and A-6 materials which constituent 2%,
2% and 2% of the sub grade soil, respectively.
Samples of sub grade were delivered to Stadia Engineering Works Consultant central laboratory for
the relevant quality tests. In performing the laboratory tests, AASHTO and BS testing methods have
been used. 51 samples of sub-grade materials were collected from the road segments alignment at
every 0.5km interval to assess the properties of the road bed materials. Classification tests (sieve
analysis, atterberg limits, linear shrinkage and natural moisture content) and modified proctor, three
point CBR and swell tests were conducted on samples collected at interval of 0.5km.
The laboratory determined CBR Values were analysed carefully, and a fairly homogeneous sections
based on the CBR values were determined. For this purpose, methodology recommended by
AASHTO Pavement design guide “Analysis Unit Delineation by Cumulative Differences” has been
adopted to determine homogeneous sections with respect to the bearing strength of the sub-grade
soils.
Accordingly, the entire Chiro Town Internal Asphalt Road project has been subdividing in following
fairly homogenous sections as indicated below.
Table: Sub grade classes for the whole road sections
Section 90
Homogeneous section
Length
percentile
[km)
CBR Value
before
treatment
Sub
grade
Class
before
treatment
90 percentile 90
CBR
Value percentile
after
CBR Value
treatment
after
treatment
I. Chiro town Adminstration to Mtichu to Leila Road Segments Homogenous Section
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Determination
Section I1 (Km 0+000– Km 3+500)
3.5
2%
S1
8
S4
Section I2 (Km 3+500 – Km6+208.54)
2.708
8%
S4
15
S5
II. Muzi Tera to TTC to Qilisa Road Segments Homogenous Section Determination
Section II3 (Km 0+000– Km 3+500)
3.5
2%
S1
5
S3
Section II4 (Km 3+500 – Km6+047.38)
2.5047
2%
S1
5
S3
III Hundi gudina School to Nejubas kidest Kidanmihiret Church,Hundi gudina School to
Aschalew hotel, kebet tera to Chiro woreda office,Agriculthural research center to Oda
Bultu University, Blood bank to Genda to Quteba bono, to Sumeya bridge to Addis
ketema and Agape hotel to Agri research center to TTC, Chiro wereda office to Care
Ethiopia Road SegmentsDesign CBR of Homogenous Sections.
Section III5 (Km 0+000 to Km 2+765.67, 9.879
km 0+000 to km 0+855 km, km 0+000 to
km 1+235.88, km 0+000 to km 1+235.88,
0+000 to km 1+040.14, 0+000 to km
1%
S1
5
S3
0+518.98, km 0+000 to km 0+580,km
0+000 to km 1+647)
Design Period
Design period is the period during which the proposed pavement carries the estimated design traffic
without major reconstruction works. Only routine and ordinary maintenance works is carried out to
maintain the road to its expected minimum performance level.
For most road projects, economic analysis period of between 10 and 20 years from the date of
opening is considered. For the subject project a design period of 20 years from the year the road is
opened to traffic i.e. (2028 - 2047) is considered for geometric design. The project road is expected
to be opened to traffic in the year 2028.
Table: Schedule for Implementation of the Project
Activity
Period
Completion of Detail Design and tender process.
End of 2023
Construction (5 years starting Beginning of 2024)
2024-2027
Completion of the construction
End of 2027
Open for traffic
Beginning of 2028
Design Period (20 years)
2028-2047
In the design of the pavement, the sub-grade design CBR values and Traffic classes obtained as
discussed above will be used. The design is carried out by ERA Flexible Pavement Design manual,
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2013. The design parameters together with the design chart have been used to design pavement
structure.
Traffic Loading
Damage to a road pavement is not purely a function of the amount of traffic but rather the wheel or
axle loading from the traffic. Light cars and vans have little effect on a pavement whilst heavily
loaded trucks have a major impact.
The vehicle damage factor is a multiplier for converting the number of commercial vehicles of
different axle loads to the number of standard axle load repetitions. Design of the pavement structure
is based upon the cumulative number of 8.16 tone equivalent standard axles (ESA) that will pass
over the road during the design period.
Equivalency factors as recommended by ERA Pavement Design Manual have been used to convert
the axle load spectrum into an equivalent number of standard axles. It has been ascertained that the
damaging effect of axles on flexible pavement is approximately proportional to the 4.5th power of the
axle load as its computed using Liddle’s formula.
The traffic study and detail analysis for of the subject road project revealed that, the expected
number of cumulative equivalent standard axles over the design life of the project road (i.e.20 years’
design period) for Chiro Town Internal Road Project is classified in the following table of traffic Class
according to ERA's design manuals, 2013.
Table: Design Traffic Classes
Station.
No
1
2
3
4
Project Road Segments
Cumulative
number
of Traffic
Remark
ESAs (106)
class
Road segment 6 and 7
0.656
T2/LV5 As per ERA PDM, 2013
Road segment 2 and 10
4.33
T5
As per ERA PDM, 2013
Road segment 3
2.45
T4
As per ERA PDM, 2013
Road segment 1-1
3.66
T5
As per ERA PDM, 2013
Road segment 1-2
3.32
T5
As per ERA PDM, 2013
Road segment 5
1.26
T3
As per ERA PDM, 2013
2.423
T4
As per ERA PDM, 2013
Road segment 4,8 and
9
Pavement Thickness
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In the design of the pavement, the sub-grade design CBR values and Traffic classes obtained as
discussed above will be used. The design is carried out by using ERA’s Flexible Pavement design
manual (2013).
Table summery of sub grade and traffic class for the section of the road Segments.
90 percentile CBR Value 90
Homogeneous section
after treatment
percentile Traffic class
CBR Value after
treatment
I. Chiro town Adminstration to Mticho to Leila Road Segments Homogenous Section Determination
Section I1 (Km 0+000– Km 3+500)
8
S4
T2/LV5
Section I2 (Km 3+500 – Km6+208.54)
19
S5
T2/LV5
II. Muzi Tera to TTC to Qilisa Road Segments Homogenous Section Determination
Section II3 (Km 0+000– Km 3+500)
5
S3
T5
Section II4 (Km 3+500 – Km6+047.38)
5
S3
T5
III.1 Hundi gudina School to Nejubas kidest Kidanmihiret Church
Km 0+000 to Km 2+765.67
5
S3
T2/LV5
III.2 kebet tera to Chiro woreda office and Chiro wereda office to Care Ethiopia
km 0+000 to km 1+235.88 and km
0+000 to km 1+647
5
S3
T5
S3
T3
III.3 Agricultural research center to Oda Bultu University
km 0+000 to km 1+235.88
5
III,Hundi gudina School to Aschalew hotel, Blood bank to Genda to Quteba bono, to Sumeya bridge
to Addis ketema and Agape hotel to Agri research center to TTC Road SegmentsDesign CBR of
Homogenous Sections.
Section III5 (, km 0+000 to km 0+855
km, 0+000 to km 1+040.14, 0+000 to 5
S3
T4
km 0+518.98, km 0+000 to km 0+580)
The ESAL for the road segments of Chiro town administration to Mitcho to leila is 0.656 Million. Even
though 0.656 million ESAL is at the border of T3 traffic class, and manuals recommend to take the
next traffic class in such cases. The above table indicates the combination of the homogenous sub
grade class with that of the Traffic class as studied by the consultant
Hence, the road Segments are designed using ERA Flexible Pavement Design Manual, 2013, Chart
B1 with thin (50mm) Flexible AC Surfacing, Granular Road Base to meet the desired pavement
surfacing thickness to withstand the traffic load in the design period. The thicknesses as adopted
from the charts is presented in the tables below.
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Table: Pavement thickness as per ERA 2013 Flexible Pavement Design Manual Chart B1
Pavement Layer Thickness (mm)
Sub grade
Design Sub Sub
Station
grade CBR grade
at
Traffic Surfa
Base
class
cing
course
AC
CBR>100
(mm)
% (mm)
93% class
MDD
Sub base
CBR>30
% (mm)
Remark
Improved
subgrade
CBR>15
%
I. Chiro town Adminstration to Mticho to Leila Road Segments Homogenous Section Determination
Section
I1
(Km
0+000– Km 3+500)
Section I2 (Km 3+500
– Km6+208.54)
8
S4
T3
50
175
150
-
19
S5
T3
50
150
100
-
ERA
PDM,
2013, Chart B1
ERA
PDM,
2013, Chart B1
II. Muzi Tera to TTC to Qilisa Road Segments Homogenous Section Determination
Section
II3
(Km
5
S3
T5
50
175
200
150
– 5
S3
T5
50
175
200
150
0+000– Km 3+500)
Section
II4
(Km
3+500
Km6+047.38)
ERA
PDM,
2013, Chart B1
ERA
PDM,
2013, Chart B1
III.1 Hundi gudina School to Nejubas kidest Kidanmihiret Church
Km
0+000 to Km
2+765.67
5
S3
T3
50
175
150
100
ERA
PDM,
2013, Chart B1
III.2 kebet tera to Chiro woreda office and Chiro wereda office to Care Ethiopia
km
0+000
1+235.88
to
and
km
ERA
km 5
S3
T5
50
175
200
150
175
150
100
PDM,
2013, Chart B1
0+000 to km 1+647
III.3 Agricultural research center to Oda Bultu University
km
0+000
1+235.88
to
km
5
S3
T3
50
ERA
PDM,
2013, Chart B1
III,Hundi gudina School to Aschalew hotel, Blood bank to Genda to Quteba bono, to Sumeya bridge to Addis
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ketema and Agape hotel to Agri research center to TTC Road SegmentsDesign CBR of Homogenous Sections.
Section
III5
(,
km
ERA
0+000 to km 0+855
km,
0+000
to
km
1+040.14, 0+000 to
km
0+518.98,
2013, Chart B1
5
S3
T4
50
175
200
100
km
0+000 to km 0+580)
Sources of Construction Materials
In conjunction with the subgrade soils, the investigations of the available construction materials were
carried out in the project area. The investigation includes:
 Natural granular materials for gravel wearing course and subbase,
 Quarry stone for the production of aggregates for concrete and masonry works,
 Borrow material for embankment and improved sub grade,
 Water for compaction and concrete work and
 Sand for concrete and mortar works.
 Detailed investigation of material sources plays an important role in assisting the design of
cost effective pavements by enhancing efficient use of the locally available construction
materials. The construction materials investigation undertaken for the design of the road
involved searching for and identification of suitable borrow pits and quarries which could
provide an adequate quality and quantity of road construction materials within the vicinity of
the road project.
 After identifying the potential material sources representative samples were taken for
laboratory testing to establish the quality and suitability of the locally available road
construction materials.
 Estimates of quantity was carried out for rock, gravel and borrow materials. This is done with
the aid of hand held GPS to record the coordinate of the boundaries of the suitable materials.
Area of the material is then calculated from the coordinates and the depth of usable material
is measured from the test pits, and the quantity estimated from the area and the depth of the
usable material. The depth of overburden material is also estimated and evaluated if the
suitable material can be exploited economically.
The potential sources of construction materials in the vicinity of the project area was investigated
through the following activities:

PDM,
A desktop study of available information: The information that was studied includes
geological maps, geological reports and topographical maps.
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Interaction with local people and relevant bureau: Local people in the vicinity of the

route and relevant bureau such as rural road authorities were enquired about the
existence of potential sources of construction material.
Field survey for potential sources: All potential sources were visually inspected and

evaluated. Samples were taken if the material was considered suitable for the intended
purpose.
Laboratory tests were conducted on material samples: This was carried out to

assess the material quality and compare the results with the required materials
specifications.
In general, prior to locating each kind of construction materials the following factors were considered:


Performance of the materials which were used for the construction of the existing road;

Accessibility;

Quantity and Quality;

Type and thickness of overburden materials;

Availability of adequate space for erecting crusher and stockpiling; and

Environmental and social aspects
Taking into account these factors Six (6) potential sources of construction materials were located,
which include possible sources of rock, natural gravel sources, and water. Moreover,
representative samples were collected from those sources for further investigation of their quality
in the laboratory.
Natural Gravel for sub base, Capping Layer and Embankment
The project road shall be constructed to the required standard that requires adequate quantity of
materials for strong lower pavement layers at reasonable intervals. Special attention is therefore
given to locating natural gravel sources that can be used for this pavement layers (i.e., sub base and
capping layers). h brown silty sandy GRAVEL (Cinder material).
Grey GRAVEL SILTY with SAND & CLAY and brown weathered GRAVEL silty clay sources could
be identified at the Vicinity for all road segments. However, natural granular materials that comply
with specification requirements for their use as sub base layers without further processing are often
rare. This is mainly due to inconsistency in their grading as a result of frequent change in weathering
pattern and extreme variability of geological processes that are responsible for their present state of
occurrences.
The locations of some road segments lie with in Chiro town. Therefore, there is no construction
material along the road segments corridor and assessed around the vicinity of the town. The quality
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of the materials exhibits significant variation within a source that consideration has been given to
selective production, and sampling of the materials has been carried out accordingly.
Accordingly, four (4) sources of natural gravel materials have been located and all source samples
were taken from the borrow sites within the vicinity of the road Segments.
Rock sources for Surfacing, Base, Concrete and masonry works
During the field investigation, the quality and quantity of rocks, accessibility of the quarry locations,
the overburden material depth and the suitability of the material for construction purposes are well
assessed. Besides, the environmental and social impacts which may arise following the utilization of
the rock quarry like displacement of local residents, claim for farm lands are assessed.
Possible rock sources for aggregate for asphalt concrete, base course, concrete and masonry works
are available within reasonable hauling distance. The quantity of available material has also been
estimated. Ease of mining and development of quarry faces and suitability to erect a crusher plant
have been considered as additional factors.
Two (2) quarry sites and one masonry stone source are Sampled from 3 quarry and one masonary
identified source along the road project which is considered as suitable by visual inspection which
can likely be sources of base course, asphalt concrete, surfacing, concrete aggregates and masonry
stone. From both source representative samples are collected to be tested at central laboratory to
confirm their suitability for the intended purposes.
The formation and characteristics of the rock sources along the road corridor is fresh to slightly
weathered Basaltic formation for Aggregate quality test and Ignimbrite rock type for Masonry.
Representative sample has been taken from the identified sources for further laboratory testing.
The summary of the laboratory test results on the rock quarry samples is presented in Annex-III.
Note that test for flakiness index is not included here; it shall be conducted during construction after
erection of crusher plant.
Natural Sand Sources /Fine Aggregate
Natural sand is not available within the project area. The city communities used from mieso river
sand (23km from chiro town), therefore we recommended to use this source with crushed sand by
appropriate blending.
Water Sources for Construction
Water samples were collected from one identified potential water sources for PH, total dissolved
solids, Cl and Sulphate content tests to check the quality of the water for the construction works.
The PH values for all tested samples showed that they are within ERA’s specification limits for
concrete works. The results of chemical analysis also revealed that the amount of the total dissolved
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solids (TDS), Sulphate content and the Chloride content are much lower than the maximum limit in
ERA’s specification requirements. The test result on water samples, along with the corresponding
specification requirements is given in the Table below.
Table: Summary of Laboratory Test Results of water sources
S.
GPS
Chainage
No.
Coordinate km
1
0+370
Location
E=705300,
Cross
N=1005052
segment
Sample Type
road perennial
River Water
ERA Standard Technical Specification (2013)
TDS
PH
7 to 9
Water for Concrete Works
content
content
(mg/l)
(mg/l)
5.87
6.54
220
2000
500mg/l
400mg/l
Mg/l max.
max.
max.
(mg/l)
6.9
Sulphate Chloride
Structural Design
Major Structures
There are five major crossings in this project which singly supported simple spans superstructures
composed RC Deck-Girder. All abutments are proposed to be made of masonry except the height of
the abutment exceeds 9m.
Table: Schedule of Major Structures
Arrangement
No.
1
2
Road
Name
Muzi tera to TTC
No. of Clear
Span
Height
Superstructure
24m
1
6m
RC Deck Girder
5+280
10m
1
4m
Slab Bridge
woreda 1+020
18m
2
5.5m
RC Deck Girder
0+167
7m
1
5m
Slab Bridge
0+418
10m
2
4m
Slab Bridge
Muzi tera to TTC
to Qilisa
Chiro
Span
0+378
to Qilisa
Kebet
3
segment Station
tera
to
Office
4
5
Sumeya
Bridge
to Addis ketema
Hundi
gudina
school
to
Nejubas
kidane
Substructure
Masonry Abutment and
Wing-wall
Masonry
Abutment,
Wing-wall and Pier
Masonry Abutment and
Wing-wall
Masonry Abutment and
Wing-wall
Masonry Abutment and
Wing-wall
mihiret
*Span rearranged from hydraulic recommendation for structural standard and construction simplicity
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Minor Structures
Along the project route, 66 crossings have been recommended for minor drainage structures by the
hydrologist. Of which 54 is Reinforced Concert pipe culverts and the remaining are adopted as either
Reinforced Concert Box or Reinforced Slab culverts. Almost all of the existing culverts are replaced
mainly due to hydraulic inadequacy because they are mostly silted up.
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INTRODUCTION
1.1
Background
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The Oromia Roads and Logistics Bureau (ORLB) has allocated funds towards the consultancy
services to carry out a Route Selection, Feasibility Study, Topographic Survey, and Drainage Facility
Study, Detailed Engineering Design and Tender Document preparation and Economic Evaluation for
Chiro Town Internal Asphalt Road Project. The Oromia Roads and Logistics Bureau (ORLB) invites
all eligible local Road Consultants for Consultancy Services for Topographic Survey, Drainage
Facility Study, Detailed Engineering Design, Tender Document Preparation and Economic
Evaluation of Chiro Town Internal Asphalt Road Design Project.
ORLB has been given the mandate for the construction, restoration, expansion and maintenance of
Regional road network. Its goal is to improve transport operating efficiency and reduce road
transport costs, provide access to rural, neglected and food-deficit areas and develop institutional
capacity of the sector.
Accordingly, The Oromia Roads and Logistics Bureau (ORLB) has employed Stadia Engineering
Works Consultant for the consultancy for Route Selection, Feasibility Study, Topographic Survey,
Drainage Facility Study, Detailed Engineering Design and Tender Document preparation and
Economic Evaluation for Chiro Internal Town Asphalt Road Project.
The objective of the project is to complete the road to Asphaltic concrete standard.
The objectives of the consultancy services are:
Phase I
3. Route selection and Topographic Survey
4. Feasibility Study including Preliminary Design, Environmental and Social Impact Assessment
(EIA)
Phase II
3. Detailed Engineering Design including preparation of tender Documents, Roads network
Development and
4.
Submission of Resettlement Action Plan (RAP)
The progression of the Consultancy from Phase I to Phase II will depend on the results of the
Feasibility Study, and the EIA. If the results show that the road is not viable for the proposed
construction, then Phase II shall not be undertaken. As such, each phase of the Consultancy shall
be priced separately. Authorization for the commencement of Phase II will be given by ORLB based
on the viability of the project. It will also be based on the performance of the Consultant during
Phase I.
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Contract Data and Management
Table 1- 1: Contract Data
Consultancy Services for Topographic Survey, Drainage Facility
Name of the Consultancy services
Study,
Detailed
Engineering
Design,
Tender
Document
Preparation and Economic Evaluation of Chiro Town Internal
Asphalt Road Design Project.
Project No.
ORA/NCB/RFP/DP-03/2015
Source of Fund
Oromia Roads & Logistics Bureau
Consultant
Stadia Engineering Works Consultant PLC
Employer
Oromia Roads & Logistics Bureau
Topographic
Type Of Service
Survey,
Drainage
Facility
Study,
Detailed
Engineering Design and Tender Document Preparation and
Economic Evaluation
Project Period
6 Months
Consultancy Contract:
Signed on
13st of March 2023
Commencement Date
24th of March 2023
Phase One services
Route
Selection
Preliminary
Planned Duration
and
Design,
2 months
Survey,
Feasibility
Environmental
Study,
including
Social
Impact
and
Assessment (EIA)
Phase Two services
4 months
Detailed Engineering Design including preparation of bidding
Documents and Resettlement Action Plan (RAP).
Expected Completion Date
Before September 24th, 2023
Project Cost:
ETB 6,007,104.06 including 15% VAT
1.3
Scope of Services and Objectives
The objectives of the consultancy services are:
Phase I
1. Route selection and Topographic Survey
2. Feasibility Study including Preliminary Design, Environmental and Social Impact Assessment
(EIA)
Phase II
3. Detailed Engineering Design including preparation of tender Documents, Roads network
Development and
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4.
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Submission of Resettlement Action Plan (RAP)
The progression of the Consultancy from Phase I to Phase II will depend on the results of the
Feasibility Study, and the EIA. If the results show that the road is not viable for the proposed
construction, then Phase II shall not be undertaken. As such, each phase of the Consultancy shall
be priced separately. Authorization for the commencement of Phase II will be given by ORLB based
on the viability of the project. It will also be based on the performance of the Consultant during
Phase I.
1.4
Project Description
Table 1- 2: Project Description
Project Name
Chiro Town Internal Asphalt Road Design Project.
Region / Zone
Oromia Regional State
Climate Classification
Weina Dega (warm-cool)
Elevation (m) (min – max)
1800 masl
Table 1- 3: Project Control Points
Road
No.
1
2
3
Estimated
Ending Coordinate
(m)
X
Y
X
Y
6.03
20
704,907.14
1,004,944.29
707,296.45
1,001,481.38
1.24
20
705,222.10
1,004,136.73
705,730.29
1,003,040.90
0.53
10
705,353.41
1,003,681.64
704,890.53
1,003,477.18
Reserch 0.60
15
705,731.73
1,002,026.05
705,982.75
1,002,558.23
1.24
15
705,796.53
1,002,169.53
704,836.32
1,002,795.65
6.20
20
704,815.41
1,005,088.68
703,096.70
1,007,957.20
Gudina 2.54
15
704,754.37
1,002,732.91
703,357.29
1,000,699.48
Project Name
Length
(km)
Muz tera –TTCQilisa
Kebt tera-Chiro
Wereda Office
Sumeya BridgeAddis Ketema
Agape
4
Starting Coordinate
Agri
Width
Hotel-
Center-TTC
Agri
5
Reserch
Center-ODA
Bultu UniversityMain Asphalt
Chiro
6
Town
AdministrationMtichu-Leila
7
Hundi
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Road
No.
Estimated
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Starting Coordinate
Ending Coordinate
(m)
X
Y
X
Y
0.85
10
704,727.37
1,002,609.02
705,419.07
1,002,280.64
Blood
Bank-
Gende
Kuteba 0.83
15
704,945.35
1,004,041.09
704,246.57
1,003,715.79
Wereda
10
705245.99
1004044.36
704908.248
1005522.819
Project Name
Length
(km)
Width
Scl-Nejebac
Kidane Mihret
Hundi
8
Gudina
Scl-Aschalew
Hotel
9
Bono
Chiro
10
Office
–Care 1.60
Ethiopia
Total Length
21.66
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Figure 1- 1: Location Map
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REVIEW OF PREVIOUS STUDIES
2.1
Route Assessement
2.1.1
Route Identification
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During route identification process, public consultations about the project and potential alternative
routes have been conducted with Chiro town administrators. During the consultation and site
assessment, we were able to identify the road segments. The proposed route segments are 10
grouped into three sections and are listed below,
Table 2- 1: Road segments of the project
Road
No.
Estimated
Length
(km)
6.04
Project Name
1
Muz tera –TTC-Qilisa
Kebt
tera-Chiro
2
1.22
Wereda Office
Sumeya
Bridge3
0. 51
Addis Ketema
Agape
Hotel-Agri
4
0.58
Reserch Center-TTC
Agri Reserch CenterODA
Bultu
5
1.23
University-Main
Asphalt
Chiro
Town
6
Administration6.17
Mtichu-Leila
Hundi Gudina Scl7
Nejebac
Kidane 2.54
Mihret
Hundi Gudina Scl8
0.86
Aschalew Hotel
Blood Bank-Gende
9
0.83
Kuteba Bono
Chiro Wereda Office
10
1.6
– Care Ethiopia
Total Length
21.66
Table 2- 2: Road segment class
Road
No.
Starting Coordinate
X
Y
Ending Coordinate
X
Y
20
704,907.14
1,004,944.29
707,296.45
1,001,481.38
20
705,222.10
1,004,136.73
705,730.29
1,003,040.90
10
705,353.41
1,003,681.64
704,890.53
1,003,477.18
15
705,731.73
1,002,026.05
705,982.75
1,002,558.23
15
705,796.53
1,002,169.53
704,836.32
1,002,795.65
20
704,815.41
1,005,088.68
703,096.70
1,007,957.20
15
704,754.37
1,002,732.91
703,357.29
1,000,699.48
10
704,727.37
1,002,609.02
705,419.07
1,002,280.64
15
704,945.35
1,004,041.09
704,246.57
1,003,715.79
10
705245.996
1004044.36
704908.248
1005522.819
Width
(m)
Project Name
Estimated
Width
Road
Length (km)
(m)
Class
1
Muz tera –TTC-Qilisa
6.04
20
CS2
2
Kebt tera-Chiro Wereda Office
1.22
20
CS2
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Estimated
Width
Road
Length (km)
(m)
Class
3
Sumeya Bridge-Addis Ketema
0. 51
10
LS1
4
Agape Hotel-Agri Reserch Center-TTC
0.58
15
CS1
5
Agri Reserch Center-ODA Bultu University-Main Asphalt
1.23
15
CS1
6
Chiro Town Administration-Mtichu-Leila
6.17
20
CS2
7
Hundi Gudina Scl-Nejebac Kidane Mihret
2.54
15
CS1
8
Hundi Gudina Scl-Aschalew Hotel
0.86
10
LS1
9
Blood Bank-Gende Kuteba Bono
0.83
15
CS1
10
Chiro Wereda Office – Care Ethiopia
1.6
10
LS1
Total Length
21.66
Pictorially they can be shown as:
Figure 2- 1: All the Project road segments of Chiro Town Internal Asphalt Road Project
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Figure 2- 2: Roads from Muz Tera to TTC, Kebt Tera to Aana Ciro, Sumayewu Bridge to Addis
Ketema, Agape Hotel to Agricultural research institute then to TTC, Agricultural Research Institute
to Odaa Bultum University, Chiro town administration to Madhicho No 2 School then Madhicho
No.9 (Leyila), Hundi Gudina Scl-Nejebac Kidane Mihret, Hundi Gudina Scl-Aschalew Hotel, Blood
Bank-Gende Kuteba Bono.
Segment 1 Road
Figure 2- 3: Roads from Muz Tera to TTC
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Segment 2 Road
Segment 3
Figure 2- 4: Roads from Kebt Tera to Aana Ciro and Sumayewu Bridge to Addis Ketema
Segment 5 Road
Segment 4
Figure 2- 5: Roads from Agape Hotel to Agricultural research institute then to TTC and Agricultural
Research Institute to Odaa Bultum University
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Segment - 6 Road
Figure 2- 6: Roads from Chiro town administration to Madhicho No 2 School then Madhicho No.9
(Leyila)
Segment -
Segment -7
Figure 2- 7: Hundi Gudina Scl to Nejebac Kidane Mihret(S7) & Hundi Gudina Scl-Aschalew
Hotel(S8)
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Segment -9 Road
Figure 2- 8: Blood Bank to Gende Kuteba Bono(S9.1,S9.2,S9.3,S9.4,S9.5).
Figure 2- 10 Chiro Wereda Office-Care Ethiopia
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Chiro is a town in eastern Ethiopia. It is the administrative center of the West Hararghe Zone in
Oromia Regional State. Located in the West Hararghe Zone in Oromia Regional State, Ethiopia.
Surrounded by Chiro rural Wereda s’ kebele. It has a latitude and longitude of 9°05′N 40°52′E and
an altitude of 1812-1840 meters’ elevation.
It was found necessary to repair, expand and maintain of Oromia region’s road network to improve
transport operating efficiency and reduce road transport costs, provide access to rural, neglected
and food deficit area and develop institutional capacity of the sector.
ORLB, as it is the authority responsible for the construction and administration of roads within the
Oromia Region and as part of the Region Administration, took the responsibility of working on the
roads within and in the vicinity of the project area to respond to the expected demand.
Current condition of the project Road segments has been assessed during the reconnaissance site
visit and the following has been noted:
Roads from Muz Tera to TTC, Kebt Tera to Aana Ciro, Sumayewu Bridge to Addis
Ketema,
Agape Hotel to Agricultural research institute then to TTC, Agricultural Research Institute to Odaa
Bultum University, Chiro town administration to Madhicho No 2 School then Madhicho No.9
(Leyila).
Muz Tera to TTC
The alignment starts at an intersection of Addis Ababa - Diredaw asphalt road on the Left side
when travelling from Addis to Diredaw and there is an existing road some length of it is Coblstone
and the rest length it is an earthen road.
The excising road way width is not enough for the recommended width on the master plan of the
town therefore there will be ROW issue during implementation. The Road crosses Sumayewu
River after it goes 400m. Bajaje, Isuzu and Small Vehicles are main means of transport at this
specific road segment. The route passes though rolling and mountainous topography.
Kebt Tera to Aana Chiro
The alignment starts at an intersection of Chiro Inter main asphalt 2 road on the Left side when
travelling from Addis to Diredaw and end by creating an intersection on Muz Tera to TTC and there
is an existing road some length of it is Coblstone and the rest length it is an earthen road. The land
use along the route is mixed residence for a short distance from the beginning and after then it is
mainly residential.
The excising road way width is not enough for the recommended width on the master plan of the
town therefore there will be ROW issue during implementation. The Road crosses Sumayewu
River after it goes 200m.Bajaje is the only means of transport due to incapability of the existing
bridge condition at this specific road segment.
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The route passes though rolling topography.
Sumayewu Bridge to Addis Ketema
The alignment starts at an intersection of Kebt Tera to Aana Chiro asphalt road around 480m on
the right side when travelling from Aana Chiro to Kebt Tera. The route has an existing Coble stone
road throughout its length which goes on the proposed road corridor. The existing route cross
Sumayewu River after it goes 100m.
The land use along the route is mixed residence for a short distance from the beginning and after
then it is mainly residential. The existing road way width is wide enough for the recommended
width on the master plan of the town, Hence, big ROW issue is not expected. Bajaje, Isuzu and
Small Vehicles are main means of transport at this specific road segment up to Sumayewu river.
This route passes through flat to rolling topography.
Agape Hotel to Agricultural research institute to TTC
The alignment starts at an intersection of Addis Ababa - Dire Dawa asphalt road on the Left side
when travelling from Addis to Dire Dawa and The route has an existing Coblstone road throughout
its length which goes on the proposed road corridor.
The land use along the route is mixed residence for a short distance from the beginning and after
then it is mainly residential. The existing road way width is wide enough for the recommended
width on the master plan of the town. Hence, big ROW issue is not expected. Bajaje, Isuzu and
Small Vehicles are main means of transport at this specific road segment.
This route passes through flat to rolling topography.
Agricultural Research Institute to Odaa Bultum University
The alignment starts at an intersection of Agape Hotel to Agricultural research institute to TTC road
around 200m on the left side when travelling from Agape Hotel to Agricultural research institute to
TTC road. The route has an existing Cobblestone road throughout its length which goes on the
proposed road corridor.
The land use along the route is mixed residence for a short distance from the beginning and after
then it is mainly residential. The existing road way width is wide enough for the recommended
width on the master plan of the town. Hence, big ROW issue is not expected. Bajaje, Isuzu and
Small Vehicles are main means of transport at this specific road segment.
This route passes through flat to rolling topography.
Chiro town administration to Madhicho No 2 School then Madhicho No.9 (Leyila).
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The alignment starts at an intersection of Addis Ababa - Dire Dawa asphalt road on the Right side
when travelling from Addis to Dire Dawa and there is an earthen existing road. The excising road
way width is not enough for the recommended width on the master plan of the town therefore there
will be ROW issue during implementation. Bajaje, Isuzu and Small Vehicles are main means of
transport at this specific road to half of the segment.
The route passes though rolling and mountainous topography.
Hundi Gudina Scl to Nejebac Kidane Mihret
The alignment starts at an intersection of Addis Ababa - Dire Dawa asphalt road on the Right side
when travelling from Addis to Dire Dawa and there is an earthen existing road. The excising road
way width is not enough for the recommended width on the master plan of the town therefore there
will be ROW issue during implementation. Bajaje, Isuzu and Small Vehicles are main means of
transport at this specific road segment. The route passes though rolling topography.
Hundi Gudina Scl-Aschalew Hotel.
The alignment starts at an intersection of Hundi Gudina Scl to Nejebac Kidane Mihret road around
120m on the Right side when travelling from Hundi Gudina Scl to Nejebac Kidane Mihret road. The
route has an existing earthen road throughout its length which goes on the proposed road corridor.
The land use along the route is mixed residence for a short distance from the beginning and after
then it is mainly residential. The excising road way width is not enough for the recommended width
on the master plan of the town therefore there will be ROW issue during implementation. Bajaje,
Isuzu and Small Vehicles are main means of transport at this specific road segment.
The route passes though rolling topography.
Blood Bank to Gende Kuteba Bono.
The alignment starts at an intersection of Addis Ababa - Dire Dawa asphalt road on the Right side
when travelling from Addis to Dire Dawa and there is an earthen existing road. The excising road
way width is not enough for the recommended width on the master plan of the town therefore there
will be ROW issue during implementation. Bajaje, Isuzu and Small Vehicles are main means of
transport at this specific road segment.
The route passes though rolling and mountainous topography.
Chiro Wereda Office-Care Ethiopia
The alignment starts at an intersection of Kebt Tera-Ana Chiro road around 1+140m on the Right
side when travelling from Kebt Tera to Ana Chiro road. The route has an existing Coble stone road
throughout its length which goes on the proposed road corridor.
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The land use along the route is mixed residential and commercial center. The excising road way
width is enough for the recommended width on the master plan of the town therefore there no
ROW issue during implementation. Bajaje, Isuzu and Small Vehicles are main means of transport
at this specific road segment.
The route passes though rolling topography
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3
TOPOGRAPHICAL SURVEY
3.1
Introduction
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Topographic survey is one of the most important and crucial field tasks that form the base data for
the project design. The topographic survey is basic pre - requisite to capture all the physical futures
along the project corridor to enable the selection of feasible and most useful alignment and later to
design and to facilitate the establishment of final centreline of the project road and land acquisition
requirements. The topographic survey work methodology consists of following main tasks.

Establishment of geodetic control points using the most important technological advance in
surveying that is the Global Positioning System (GPS)

Setting up of permanent beacons to serve as a reference system during road design and
construction

Development of control traverse-line and geometric level-line.

Detailed field survey using electronic Theodolite with EDM (Total Stations) and digital
Levels, which will have a different precision according to the topographic operations.

Data Processing and CAD;

Development of Land acquisition plan; and

Delivery of survey Report including Diagrams and Monographs

Ground surface and Structural location survey
For carrying the survey work the consultant approached EMA (Ethiopian Mapping Authority) and
collected EMA control points within the Project Corridor and deployed high and precision
instruments like GPS, Total station, and Auto level in compliance to the TOR.
3.2
Mobilization of Surveyors and Equipment’s
The survey instrument used in this project and their accuracy are mentioned below.
Table 3- 1: List of Survey instruments
S/No
1
2
Survey Instrument
Ground
positioning
system instruments
Total Station
Model/ make No
Promark
Three
Degree of Accuracy
Magellan
navigation system Thales GPS
system receiver sets
Static Mode with at least 8 satellites
tracking per site (5 mm + 0.5ppm)
Sokkia Set 310, Nikon, Topcon 2’’ and 3’’
With a maximum tolerance in mm
3
Level
Sokkia
for single section equal to: 10K,
where  is the distance in km.
In order to achieve the required output within time the limit, the consultant deployed three teams.
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Table 3- 2: List personnel’s (team 1: GPS team)
No
Name of staff
Job Title
Position on the Project
1
Yonas Tegegne
S.Surveyor
Coordinator/ Surveying Team leader
S.Surveyor
Surveyor
2
Table 3- 3: List personnel’s (team 2: Control traverse survey& Topographic Survey)
No
Name of staff
Job Title
Position On the Project
1
Abenezer Buche
S.Surveyor
Senior Surveyor (Team Leader)
2
Wendifraw
S.Surveyor
Senior Surveyor
3
Semahegn Solomon
S.Surveyor
Senior Surveyor
3.3
Data Collection
Data collection is the first stage of topography surveying which has been conducted in two stages,
Desk study and Site reconnaissance. During desk study relevant information have been collected
from topographical maps, satellite imageries, Google earth maps and GPS Control point
information have been collected from Ethiopian Mapping Agency.
The list of data collected and used in each category includes:
a) 1:50,000 scale topographic mosaic map of Ethiopia
b) 12.5mX12.5M DEM Grid data- Shuttle Radar Topography Mission (SRTM) data
c) List of National GPS control points
No
Point Name
Easting
Northing
Height
Zone
1
ASB1
685234.239
1013753.559
1491.333
37
2
MIESO(ETMI)
692840.904
1020511.073
1329.828
37
3.4
Scope of Topographic Survey
The scope and methodology of the topographic surveying works conducted in the specified
sections mainly includes
 Collection of data for route selection, route location and detail topographic surveying on the
field.
 Route location and marking of the preferred route on the field.
 Establishing GPS points at every 5km interval of the road and tying it to the National Grid
System.
 Installation of permanent benchmarks at a maximum of 100m to 300m intervals.
 Levelling of the control points with automatic level instruments
 Carrying out detailed cross-section survey at every 20m interval or lesser and with a band
width varying between 50 to 100m and beyond, depending on the terrain conditions, to the
left and right of the approximate centre line of road
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 Carrying out detail surveying at the bridge locations
 Gathering all the information required for the land acquisition related to the project
 Generating a terrain model from the survey data and using the terrain model for the
detailed engineering design of the road
3.5
GPS Surveying Methodology
3.5.1
Establishment of Geodetic Control Points Using Global Positioning System (GPS)
Global positioning system (GPS) observations were determined within approximately about 4.0
KMs interval along the road length. The geodetic GPS points were placed in highly accessible sites
with appropriate bench marks protected against impact to guaranty their stability and integrity.
The established GPS points are couple and inter visible to each other at a minimum distance of
50m and were tied with national coordinates system found within the vicinity of the project road.
The GPS points are painted yellow and the description is marked in red.
3.5.2
Tying with National Coordinate System
Generally, the project passes through Zone 37 and to secure and validate a reasonable initial new
control points have been automatically tied to the national grid system in Zone 37, reference point
Adindan (30th meridian) datum.
The coordinate system used for the project is the Ethiopian National Grid System (Clarke 1880
modified spheroid, U.T.M Grid Adindan Datum).
3.5.3
Coordinate System
The coordinate system used for the project is the Ethiopian National Grid System (Clarke 1880
modified spheroid, U.T.M Grid Adindan Datum).
The design survey control points shall be checked and correlated in to the National Grid system by
transforming in to UTM projection system and local datum reference- Adindan datum.
3.5.4
Verification of Positioning
The positions of the GPS points were checked with the National coordinates.
3.5.5
Data Processing and Mapping
We made widespread use of computerized system whilst carrying out investigation and survey
activities. This permits an easier, more efficient and rapid management and guarantees a
continuous control of all activities and aspects of the work.
Using highly post- processing GNSS Solutions software, the WGS84 co-ordinates has been
transformed into the national grid, U.T.M. co-ordinates based on Clark 1880 (Modified) spheroid –
Datum: Adindan.
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Transformation parameters
Coordinate system
Name: ETHIOPIA ZONE 37
Type: projected
Unit name: meters
Vertical datum: EGM 2008
Vertical unit: meters
Datum
Name: ADINDAN 37
Ellipsoid name: CLARKE 1880 mod
Semi-major axis: 6378249.145 m
Inverse flattening: 293.466307674
Dx to wgs84: 162.000 m
Dy to wgs84: 12.000 m
Dz to wgs84: -206.000 m
Projection
Projection class: Transverse Mercator
Latitude of origin 0° 00' 00.00000"n
Central meridian 39° 00' 00.00000"e
Scale factor 0.999600000000
False easting 500000.000 m
False northing 0.000 m
3.6
Benchmark Setup
Benchmark (secondary control points) referenced in the field on reliable points on appropriate
bench mark beacons protected against impact to guaranty their stability and integrity. These
benchmarks established at intervals of approximately 100m to 300 m. The vertical controls of the
bench marks were established using differential levelling procedure. The differences in elevation
between consecutive benchmarks / GPS points are determined which are used to extend elevation
from the first GPS point elevation to all other benchmarks and GPS points.
3.6.1
Control Traverse-Line
A traverse surveying is usually employed in all forms of legal and engineering works to compute
Easting and Northing positions for networks of benchmarks extended from GPS points. Essentially,
traverses are a series of established survey stations that are tied together by angles and distances
measured and recorded using electronic total stations between each vertex by beginning on twin
GPS points and closing on the next twin GPS points.
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The accuracy of traverse surveying is
Allowable angular accuracy
= √ (N+1) * 30”
Allowable Linear accuracy
1:10,000
The angle and distance measurements are reduced into Easting and Northing coordinates using
standard traverse computations procedures.
3.6.2
Geometric Level-Line
The elevations of the consecutive Bench marks are transformed by direct differential levelling
starting from the elevation of the first GPS point elevation using levelling instrument. Levels for
each consecutive bench marks are determined by forward and a subsequent backward run forming
a closed loop. Levels for each control points are computed using standard differential levelling
computation. For this reason, the elevations of GPS points listed on the differential levelling
overrides the list on the GPS Monograph.
The accuracy of level (Z) is:
Z = 10 mm x √K
3.7
Where (K being the survey distance in km between control points).
Collection of Cross-section Data
The topographical survey is the backbone of a detailed engineering design. Accuracy of the
information collected during this survey has a direct impact on almost all the design activities
involved in the project.
This study involves location of control points, construction and fixing of co-ordinates and
documentation of monuments.
Topography surveys are performed in order to determine the position of all natural and manmade
features within the road corridor. The topography surveying has been carried out with a minimum
of 100m band width (50m to the left and 50m to the right from the centre of the road) varying up to
300m band width and a maximum staking interval of 20m. Where there is a high cross slope, the
band width is increased in order to provide design flexibility and accommodate the design cross
section.
The survey included the determination of the coordinates of points located:
 on the existing road centreline
 at the road edges
 at the toe line of the fill and cut sections
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 break lines and points on Culverts and Bridges
 high water marks
 break lines and points along longitudinal section of rivers 100 m either side in the case of
minor bridges and 500 m either in the case major bridges
 cross section of rivers
 features on intersections and side roads up to a length of 50m
 features showing service lines
 buildings
 places of social or traditional importance
3.8
Data Processing and CADD
The consultant uses computerized system whilst carrying out investigation and survey activities.
This permits an easier, more efficient and rapid management and guarantees a continuous control
of all activities and aspects of the work.
Specific programs are used to transfer and process field data into computers. Computer programs
such as AutoCAD are used for preparation of drawings and graphics, using software modules that
operate inside AutoCAD that are specifically designed for maps and for road projects.
The electronic field books and other topographic data are placed in ASCII and / or DXF formats or
MS Excel files.
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4
HYDROLOGICAL AND HYDRAULIC STUDY
4.1
Project Description
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Chiro is a town in eastern Ethiopia. It is the administrative center of the West Hararghe Zone in
Oromia Regional State. Located in the West Hararghe Zone in Oromia Regional State, Ethiopia.
Surrounded by Chiro rural Weredas’ kebele. It has a latitude and longitude of 9°05′N 40°52′E and
an altitude of 1812-1840 meters’ elevation.
It was found necessary to repair, expand and maintain of Oromia region’s road network to improve
transport operating efficiency and reduce road transport costs, provide access to rural, neglected
and food deficit area and develop institutional capacity of the sector.
ORLB, as it is the authority responsible for the construction and administration of roads within the
Oromia Region and as part of the Region Administration, took the responsibility of working on the
roads within and in the vicinity of the project area to respond to the expected demand.
Scope of Hydrology and Hydraulics Report
 The Oromia Roads & Logistics Bureau proposes to carry out Consultancy Services for
Topographic Survey, Drainage Facility Study, Detailed Engineering Design, Tender
Document Preparation and Economic Evaluation of Chiro Town Internal Asphalt Road
Design Project from which this hydrology/Hydraulics study main scope and purposes are
from which this hydrology/Hydraulics study main scope and purposes are:  To describe the design criteria and the design assumption used for the design of drainage
structures
 To describe the existing structures condition
 To give detail description of the hydrological study and hydraulic analyses and
computations made in the analysis,
 To provide a schedule that show the design discharge that must be pass under the road
due to expected floods,
 To provide a schedule that shows the drainage, size, and recommendations for specific
drainage related problems
 To give detail description of hydrological study, hydraulic analysis, computation and
evaluation of peak discharge of mention projects, evaluating and determining the type/size
of existing and proposed structure, safety of the drainage facilities needed for the proposed
alternative crossing sites and to provide hydraulic recommendations in compliance with
ERA DDM, 2013 manual guidelines and procedures.
This report is divided into seven sections including this introductory section. The second chapter
presents design standard of structures and methodology. The third chapter presents data collected
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for the study, climatic condition of the project area, drainage condition, and land use and soil type
of the watershed area of the projects.
The fourth chapter presents hydrological study, topographic map, soil type, data collected from site
and data acquired from different organizations and manuals. In this project the design flood is
estimated focus on Rational and SCS method depend on the catchment size as per
recommendation of ERADDM 2013.
The fifth chapter deals with hydraulic design of road projects with considering Economy and
sustainable drainage opening that suite the site conditions are proposed using appropriate
hydraulic computation as per the manual recommendation. Hydraulic tool box, Hy-8 and HEC-RAS
hydrodynamics software is used for the hydraulic analysis of longitudinal ditch, crossing culverts,
and Bridge opening sizing, and determination respectively. The sixth chapter discusses
conclusions and recommendations, while the final part, chapter seven, presents the
hydrology/hydraulics analysis in annex summary format.
4.2
4.2.1
Methodology and Standards
General
The ultimate goal of highway drainage design is to convey surface and stream waters originating
on the road surface and upstream of the drainage facility to the downstream side without causing
objectionable backwater, excessive flow velocities, excessive scour, or unduly affecting traffic
safety. Prior to the hydraulic design of a culvert or bridge, the design discharge, the quantity (Q) of
water in cubic meters per second that the facility may reasonably be expected to convey must be
estimated. Many hydrological guidelines recommend using peak floods for highway drainage
structures. So, the peak flood is estimated for the purpose of designing the highway drainage
structures.
This Design report was commenced by the ERADDEM 2013 manual even though the
Hydrologist/Hydraulic Engineer, additional detailed desk work for the road alignments using
satellite imageries, 1: 50,000 Topographic maps, DEM, integrating the desk work with a detailed
site visit and investigation of the site and supplemented by close consultation with the stakeholders.
4.2.2
Methodology
The method adopted for the design of flood computation and hydraulic analysis and design are
discussed briefly under this section. The study has been started by data collection, and then
interpreting and analysing the data. The result of the analysis is used for determination of design
discharge and design of drainage structures.
To conduct a hydrological study and hydraulic design of the project, the activities listed below were
performed:
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 All available data which are useful for hydrological study and hydraulic design were
collected and analyzed;
 Study on topographic maps: Watershed area delineation & determination of the catchments
area, stream lines length using available topographic maps, high degree resolution( 12.5m
by 12.5m) DEM and satellite images;

ARC-GIS with arc-hydro tool software version 10.7 is used to delineate catchment area.

Globar Mapper 23 is used to determine all catchment characteristics of the watershed
area of the Bridge site.
 Soil map and land use/cover map of the drainage areas for estimatation rainfall-runoff
characteristics of the watershed area runoff curve number are prepared;

ARCGIS 10.7 is used to analysis the soil map and landuse/cover map for the delinated
wateshed areas.
 Field investigation
was conducted to collect data on catchments characteristics, flow
pattern, possible location for alternative crossing of the bridges, characteristics at upstream
or downstream side and observed high flood marks around the crossing;.
 Estimation of design discharge for different return period using rainfall-runoff model based
on sizes of the catchments and availability of data as per the recommendation of the
manuals;
 A brief summary for the size, number, and catchment characteristics of the drainage
facilities.
4.2.3
Design Standards /Frequency
Design Frequency or return period is indicative of the frequency with which a certain magnitude of
rainfall/runoff occurs in that period. The number of times a flood of a given magnitude can be
expected to occur on average over a long period of time. Design frequency can be expressed with
probability. The probability of being equal or exceeded in any year can be defined by the following
expression.
P( X  X T ) 
1
T
Where: P = Frequency Exceedance Occurrence of design flood exceeded or equal once (Return
period), in years
Since it is not economically feasible to design a structure for the maximum runoff a watershed is
capable of producing, a design frequency must be established according to the cost, potential flood
hazard to property, expected level of service, political considerations, and budgetary constraints,
and considering the magnitude and risk associated with damages from inundation.
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The road is classified as DC5 according to the Geometric Design Standard and this governs the
design storm frequency period of cross and side drainage structures. The ERA Drainage Design
Manual (ERADDM-2013) recommends the design frequency as shown in table 2-1 for DC5 roads.
The recurrence interval values shown in the table below are used for hydraulic design of drainage
facilities.
Table 4- 1:: Return Periods Considered (ERA Drainage Design Manual 2013)
Design
Flood
Return
Period
(Years)
Type of Structure
Check Review
Flood (Years)
Artesian Road
Drains in Residential Areas, Gutters and Inlets
2
5
Side Drains and Ditches
5
10
Culvert, Pipe Span <2 m
10
25
Culvert, 2m <Span < 6 m
25
50
Short Span Bridge, 6m < Span < 15 m
25
50
Medium Span Bridge, 15 < Span < 50 m
50
100
Long Span Bridge, Spans > 50 m
100
200
4.2.4
Methods of Design Flood Computation
As per ERA DDM recommendations (Chapter nº5), the methods used in determining peak flood
magnitudes for design of road drainage structures are rational method for catchments with an area
less than or equal to 0.5 km2 and Soil Conservation Services (SCS) unit hydrograph method for
catchments with an area greater than 0.5 km2 and greater than 65 km2
Table 4- 2: Flood estimation methods (Table 5-3 of ERA DDM).
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As Per the watershed area for the project area both applied the rational and SCS method were
used for design flood computation. The basic principles of the methods are discussed in chapter
four.
Design Limitation
The study was carried out using all possible available data sources. However, some of the data are
limited to perform detail hydrological and hydraulic analysis which considers the entire watershed
in the modelling. High resolution and latest soil type and land cover/ land use map are not
available
4.3
Data Collection and Analysis
Following ERA DDM for Hydrologic/Hydraulic Analysis and Design, the Consultant collected all
relevant data required for the implementation of the design service around the project sites. These
data included but not limited to Climatic Data and Mapping & Aerial photography.
As part of planning and design, several categories of data are collected and evaluated, including:

Physical characteristics of drainage basins,

Maps and topographic data including channel surveys and cross sections,

Collection of Rainfall Data from NMSA,

Upstream constraints on headwater elevation,

Vegetation cover,

Channel and flood plain delineation and related studies,
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Consideration of multipurpose opportunities and constraints, benefit/cost analysis and
evaluation.
4.3.1
Data Collection
While dealing with the hydrologic and hydraulic design of any road/ bridge project it is very
important to outline the type of data, possible data sources, and aspect of the data collection that
are normally required for drainage analysis and design. Topographic maps, soil data and land use/
cover were collected for further the hydrological study and comparison with actual observation. The
data collected for the study as follow:

Daily highest rainfall and mean monthly rainfall records of different stations around the
project area, which is acquired from Ethiopian meteorological agency.

Long term monthly maximum and minimum temperature of different stations around the
project area, which is acquired from Ethiopian meteorological agency.

From Ethiopian mapping Agency (EMA), topographic map of scale 1: 250,000

Digital Elevation Model (DEM) of the project area (12.50m by 12.50m resolution)

Geomorphology/soil maps of the project area

Land use/cover of the project area.

Previous rainfall data analysis and study for the subject road project if any.

Detailed condition survey of drainage characteristics and existing structures if any.

Plan-Profile of the road project based on Topographic survey.

Topographic survey data of the of the bridge crossing locations
4.4
Previous Studies, Existing Data and Maps
4.4.1
Data and documents
All available data encompassing metrological, land cover, soil and topographic data has been
collected from different sources and reviewed in characterizing the drainage feature of project
under consideration. Review and realization of, employer’s requirement and related documents
has been also made.
Digital elevation model of 12.5m resolution has been used to characterize the project corridor
with respect to drainage along with 50,000 scale topographic map produced by Ethiopian
mapping Agency. Apart from digital elevation model, recent Google images of good resolution
obtained from online free sources (Google earth) and satellite images used to refine the drainage
analysis. Above all stated data, onsite stretch based physical drainage survey and local people
consultation provided a detail information about the prevailing drainage condition of the road.
Climate data from the Asebe-Teferi stations has been collected and analyzed to characterize the
area in terms of climate.
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Table 4- 3: Physiographic and climate data
S/N
Data Type
Lat.
Long.
1
12.5 m resolution DEM
9
41
Remark
Obtained
from
free
Landsat
online source
2
Topographic map
3
Metrological
data
9
41
50,000 scale sheets
(RF)&
Asebe Teferi Stations
Temperature
4
Land use/cover & soil data
Google/ Satellite image
1:1,000,0000 Scale
9
41
From free online sources with
5
20m /75yard resolution
4.4.2
Existing Conditions
General
Minor and major defined streams crossing structures exist with poor and good hydraulic
performance have been built on the road where some minor and major crossing Structure
recommended to be replaced by new structure.
The number of medium and major rivers flows across the route are considerably in number and
there are several minor and major structures are Propose.
Existing Bridge in Kebte tera to chiro wereda
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Slab Culvert in Chiro Town Administration to mitichu Leila
Bridge in Sumeya Bridge to Addis Ketema
Masonry Ditch in Muztera Tcc
Figure 4- 1: Existing Condition of Major and minor Cross Drainage Structures
Field Data
A field survey or site investigation should always be conducted except for the most preliminary
analysis or trivial designs. Hence the field survey is one of the primary sources of hydrologic data.
In the first stage, the team of different professionals carried out a reconnaissance survey in which
general drainage pattern and catchment characteristics were observed in order to prepare a
detailed investigation survey program.
The project road alignments cross a number of minor crossing and some number of major
drainage crossings. There are minor drainages found in the project road and recommended
structures are pipe culverts with different arrangement in number and slab culverts.
4.4.3
Hydro-Climatic Data
4.4.4
Climate
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Climate is influenced by latitude, altitude, land and water surfaces, mountain barriers, local
topography, and such atmospheric features as prevailing winds, air masses and pressure centers.
Although Ethiopia is located in the tropics, temperatures vary greatly with altitude and large climate
variation, from hot arid to cool temperate, exist in the country. Generally, the adiabatic lapse rate is
about 6oc decrease per 100 m altitude increase. Based on climatic classifications of Ethiopia, the
vicinity of the project area can be grouped under W Dega climate condition.
Figure 4- 2: Climatic Zones of the Project Area
4.4.5
Rainfall Data
Monthly rainfall data is used to demonstrate the rainfall pattern in & around the project areas. Thus,
the data for several years were collected and analyzed to demonstrate the variation of rainfall
prevalence in the area.
Table 4- 4: Monthly Highest Rainfall Data
Month
Monthly
Mean RF
Jan
Feb
Mar
12.3
14.9
73.5
April
109
.9
May
Jun
July
Aug
Sep
Oct
Nov
Dec
105.4
62.6
129.1
182.5
133.2
43.1
17.4
19.4
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Figure 3.6 maximum monthly rainfall data
Figure 4- 3: Mean Monthly Rainfall of Asebe Teferi
4.4.6
Frequency Analysis
The objective of frequency analysis of hydrologic data is to relate the magnitude of extreme events
to their frequency of occurrence through the use of probability distributions of Gumble EV I, LogPearson Type III, Log-Normal, Normal Distribution and Pearson Type II. The hydrologic data
analyzed are assumed to be independent and identically distributed, and the hydrologic system
producing them (e.g., a storm rainfall system) is considered to be stochastic, space-independent,
and time-independent in the classification scheme
18 years of rainfall data were collected from national meteorological service Agency at Asebe-teferi
station, based on the above methods the collected data were analyzed. The frequency analysis
result was compared with ERADDM recommendation of Rainfall region A4 and Regional Value it’s
higher than the ERADDM.The peak flood estimation were computed by using the rainfall depth of
the frequency analysis result obtained. Recommendation of Asebe Teferi Metrological analysis for
the specified return periods.
Based on the obtained meteorological data’s frequency analysis were done and the obtained result
were presented in table below
Table 4- 5: 24hr Rainfall Depth Vs Frequency
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Figure 4- 4: From NMA, IDF Curve of Asebe Teferi metrological analysis
The Watershed area for all streams crossing of the project has been delineated from 12.5mx12.5m
resolution digital elevation model through ARC-GIS with Arc-Hydro tool. Stream channel length,
slope and time of concentration have been derived from delineated watershed area for each
crossing under consideration.
4.4.7
Catchment area Delineation
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The study of the watershed characteristics extensively studied using site investigation and
topographic maps, (Data regarding catchment areas) i.e. watershed size and shape, stream slope,
stream length and land slope were determined from topographic map scale 1: 50,000 and satellite
data DEM 12.5mx12.5m resolution.
The catchment areas of each watershed on the whole route corridor were delineated from DEM
data of 12.5mx12.5m resolution and topographic map 1: 50,000. The sizes of each catchment area
were determined using Arc GIS software.
Figure 4- 5: Preliminary Delineated Watershed Area
4.4.8
Hydrologic Soil Type
The soil types of the watershed areas are examined in this section to classify the soil with respect
to infiltration and runoff i.e. to determine the runoff coefficient or curve number of catchments areas.
The soil types of the catchments area are determined from site visit as well as geomorphology and
soil maps of the project area. Soil type of the drainage areas have different rate of infiltration.
Based on infiltration rates, the soil conservation service (SCS) has divided soil into four hydrologic
soil groups as follows: Group A: Soil with a low runoff potential due to high infiltration rates.
Group B: Soil with moderately low runoff potential due to moderate infiltration rates.
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Group C: Soil with moderately high runoff potential due to slow infiltration rates.
Group D: Soils with a high runoff potential due to very slow infiltration rates.
The soil types of the watershed areas are examined in this section to classify the soil with respect
to infiltration and runoff i.e., to determine the runoff coefficient or curve number of catchments
areas. The soil types of the catchments area are determined from site visit as well as
geomorphology and soil maps of the project area.
The soil type and thickness in the project area is a function of geology, geomorphology and climate
and the hydrologic soil grouping is classified by the Ministry of Water Resources Metadata Bases
(Shape files). The Hydrologic soil grouping for each catchment is identified from examination of
available soil maps and physical assessment done on site. Accordingly, as per ERADDM2013 and
from soil map the project area catchment area is 100% HSG under B which indicates moderately
runoff potential due to moderately infiltration rate.
Figure 4- 6: Hydrologic Soil Group Map of the Project Area
4.4.9
Vegetation and Land Use
Land use and land cover for each catchment is identified from examination of available Land Use
and Land Cover maps, land use shape files and physical assessment done on site. Based on the
obtained data’s more throughout the project route the land cover was Urban and Cultivation and
Managed area
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Figure 4- 7: Land use/Cover of the Road Project Area
4.5
Hydrological Study
4.5.1
General
The hydrological study was undertaken in order to compute and evaluate peak discharges for all
watercourses crossing the project road. Calculation of these peak discharge values enabled the
determination of the hydraulic opening sizes and types of waterways required.
There are many methods developed for calculation of the design flood but their applicability
depends mainly on the availability of hydrological data. As most of the methods have parameters
which depends on climate and morphological condition. The climate data (rainfall and intensity)
and morphological condition of the project area were collected and investigated to determine
inputs data for the methods of flood calculation like runoff coefficient, curve number, design point
rainfall and rainfall intensity of the project.
The hydrological analysis was undertaken using available maps and digital terrain model together
with the data acquired from Meteorological Services Agency. Additional hydrological and
geological information has been gathered from site visits and different sources.
Rational formula and U.S. Soil Conservation Services (SCS) Unit hydrograph method were
adopted to compute the design discharge depending on the size of catchments area and
availability of stream flow data as per ERA Drainage Design Manual (ERADDM-2013)
recommendation.
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4.5.2
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Methods of Peak Flood Computations
Any hydraulic structure of road crossing should be designed in such a way that any extreme event
of peak discharge should pass safely. Hence for this particular project the hydrologic design is
carried out according to ERA Drainage Design Manual, (ERA DDM 2013) given on the employer’s
requirement of the subject road project. Salient features are reproduced herein.
There are many methods developed for calculation of the design flood but their applicability
depends mainly on the availability of hydrological data. As most of the methods have parameters
which depends on climate and morphological condition. The climate data (rainfall and intensity)
and geo-morphological condition of the project area were collected as it was cited in previous
section and investigated to determine inputs data for the methods of flood calculation like runoff
coefficient, curve number, design point rainfall and rainfall intensity of the project.
Rational formula and U.S. Soil Conservation Services (SCS) Unit hydrograph method is the most
widely used and standard method adopted by ERA for smaller to medium catchment size. The
basic principles of the methods are discussed briefly in the following subsections.
4.5.3
Rational Method
The rational methods of estimating design flood on small watershed is based, in concept, on the
criterion that storms of uniform intensity distributed evenly over the basin, maximum rate of runoff
equal to a certain percentage of rainfall intensity occurs when the entire basin area is contributing
at the outlet. This condition met after the elapsed time tc, time of concentration. The equation of
rational formula is function of Catchment area, runoff coefficient and time of concentration. The
equation is expressed as:
Qd = 0.278 C Cf I A
Where: Qd = Design Discharge in m3/sec
Cf = Frequency factor
C = Runoff Coefficient
A = Drainage area (Km2)
I = Rainfall Intensity for duration equal to time of concentration
This method is adopted for catchments area up to 0.50km2. The parameters which are used in the
computation of design flood using rational formula are discussed as follows.
i.
Runoff Coefficient & Frequency Factors
Runoff coefficient of the catchment area depends on slope/terrain characteristics, permeability of
the soil and land use/cover of catchments area. It is influenced by many variables, and does not
remain constant during the design life of the structure.
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Table 4- 6: Derived Run-off Coefficients (C)
Factor
Average
Cs
Run-off
Description
Coefficient
< 3.5% (flat)
0.05
3.5% - 10% (Flat to moderate)
0.10
of 10% - 25% (Rolling)
25% - 45% (Hilly)
catchment
0.15
>45% (Mountainous)
0.25
Well drained soil (e.g., sand and gravel)
0.05
slope
0.20
Fairly drained soil (e.g., sand and gravel with 0.10
fines)
Cp
0.15
Permeability Poorly drained soil (e.g., silt)
of soil
0.25
Impervious soil (e.g., clay, organic silts and 0.50
clay)
0.40
Water-logged black cotton soil
Rock
Cv
Dense forest/thick bush
0.05
Spares forest/dense grass
0.10
Ground
Grassland/scrub
0.15
type/cover
Cultivation
0.20
Sparse grassland
0.25
Barren
0.30
C = Cs + Cp + Cv
Table 4- 7: Run-off Coefficient (C) as per ERA Drainage Design Manual 2002)
Terrain Type
Soil Type
A
B
C
D
Flat, < 2%
0.04-0.09
0.07-0.12
0.11-0.16
0.15-0.20
Rolling, 2-6%
0.09-0.14
0.12-0.17
0.16-0.21
0.20-0.25
Mountain, 6-15%
0.13-0.18
0.18-0.24
0.23-0.31
0.28-0.38
Escarpment, >15%
0.18-0.22
0.24-0.30
0.30-0.40
0.38-0.48
The Rational equation given above is applicable for return periods of 5 to 10 years. For less
frequent flood computations, the rational equation should be multiplied by factors.
Table 4- 8: Frequency factor, Cf
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Return Period
Cf
5
1.00
10
1.00
25
1.10
50
1.20
100
1.25
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Sources: ERADDM-2013
ii.
Rainfall Intensity
18 years Daily rainfall data from Asebe Teferi station have been collected and analyzed using five
distribution methods for design storm and IDF curve development. Computed design rainfall
values found to be very close to the regional design rainfall values., however, apart from
discontinuities in rainfall records largely observed on the collected data that will make the
analysis less reliable, short duration rainfall records that can be readily used for IDF development
not obtained for the stations under considerations and only daily rainfall data used with
generalized coefficients developed on regional context making the analysis course enough. With
this ground, regional design rainfall value and IDF curve which better represent the actual flood
condition of the area has been considered to undertake hydrological analysis of the project road.
Time of Concentration
Time of concentration is the time required for water to flow from hydraulically remote point of
catchments area to the point under investigation. The most intense rainfall that contributes at
drainage structures crossing will be that the duration equal to the time of concentration.
Calculation of the Time of Concentration for Overland Flow:
Overland flow is the type of flow that occurs in small, flat or in upper reaches of catchments, where
there is no clearly defined watercourse. Run-off, then, is in the form of thin layers of water flowing
slowly over the fairly uneven ground surface. The kerby formula is recommended for the
calculation of Tc in this case. It is only applicable to parts where the slope is fairly even.
Tc=0.604(rL/S0.5)0.467
Where:
Tc = time of concentration (hours)
r = roughness coefficient obtained from Table 4-5
L = hydraulic length of catchment, measured along flow path from the Catchment
boundary to the point where the flood needs to be Determined (km)
S = Slope of the catchment
S=H/1000L (m/m)
H= Height of most remote point above outlet of catchment (m)
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Calculation of Time of Concentration for Defined Watercourses
In a defined watercourse, channel flow occurs. The recommended empirical formula for
Calculating the time of concentration in natural channels was developed by the US Soil
Conservation Service:
Tc= (0.87L2 /1000 Sav) 0.385
Where: Tc= time of concentration (hours)
r = roughness coefficient obtained from Table 1-11
L = hydraulic length of catchment, measured along flow path from Catchment boundary to
the point where the flood needs to be Determined (km)
Sav = Average slope (m/m)
The n values are a composite of information compiled by Engman (1986). 2 When selecting n,
consider cover to a height of about 0.03 m. This is the only part of the plant cover that will obstruct
sheet flow.
Table 4- 9: Roughness Coefficients (Manning’s n) for Sheet Flow
Surface Description
n1
Smooth surfaces (concrete,
0.011
asphalt, gravel, or bare soil)
Fallow (no residue)
0.05
Cultivated soils:
Residue cover < 20%
0.06
Residue cover > 20%
0.17
Short grass
0.15
Dense Grasses
0.24
Range (natural)
0.13
Light underbrush
0.4
Dense underbrush
0.8
Grasses:
Woods:2
Source: ERA Design Drainage Manual
When cross sectional information of the open channel (stream cross section parameter for the
entire reach) is acquired, the average velocity of the open channel flow can be calculated using
manning’s equation
1
V  r 2 / 3 s1/ 2 Were: V = Average velocity, m/s
n
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r = Hydraulic radius, m (equal to A/Pw)
A =Cross section area of the flow, m2
Pw =Wetted perimeter, m
S =Slope of the hydraulic grade line, m/m
n =Manning’s roughness coefficient
For small catchments areas, where the maximum elevation difference of the watershed could not
be determined on the available map scale. The velocity method is adopted. It is based on the
concept of travel time (Tv) for a flow segment is a function of length of flow (L) and the velocity.
The following equations were used:
TC 
L
60 * V
Where:
TC =
Time of concentration [minutes]
L
=
Distance from remote point to the point of crossing [m]
V
=
Average velocity [m/sec] (Table 4-4)
In order to minimize and avoid any errors in calculating time of concentration, particularly when the
average basin slope varies significantly from the mean channel slope (as in steep mountainous
areas), the time of concentration is calculated for two sections. The first one is from the low point to
0.7 point and the second one is from the 0.7 point to the end of the channel. Further subdivision of
the waterway was carried out for those streams that traverse different terrain. The rational method
of peak flood computation shown in Appendix 6 & 7 of this report.
4.5.4
SCS Unit Hydrograph Method
This method is developed by the U. S. Soil Conservation Service for calculating rates of runoff and
requires the same basic data as the Rational Method: catchment area, a runoff factor, time of
concentration, and rainfall. The SCS approach, however, is more sophisticated in that it considers
also the time distribution of the rainfall, the initial rainfall losses to interception and depression
storage, and an infiltration rate that decreases during the course of a storm. With the SCS method,
the direct runoff can be calculated for any storm, either real or fabricated, by subtracting infiltration
and other losses from the rainfall to obtain the precipitation excess.
Peak flood computation using SCS method requires the following input data;
I.
Catchment Area
One of the most important parameters which govern the amount of peak flood at a particular outlet
point is the size and shape of watershed. The catchment area will be determined from topographic
maps and field surveys.
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II.
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Rainfall
The SCS method is based on a 24-hour storm event which has a Type II time distribution. The
Type II storm distribution is a typical time distribution which the SCS has prepared from rainfall
records. It is applicable for interior rather than the coastal regions and should be appropriate for
Ethiopia. To use this distribution, it is necessary for the user to obtain the 24-hour rainfall value for
the frequency of the design storm desired.
III.
Rainfall – Runoff equation
A relationship between accumulated rainfall and accumulated runoff was derived by SCS from
experimental plots for numerous hydrologic and vegetative cover conditions. Data for landtreatment measures, such as contouring and terracing, from experimental catchment areas were
included. The equation was developed mainly for small catchment areas for which daily rainfall and
catchment area data are ordinarily available. It was developed from recorded storm data that
included total amount of rainfall in a calendar day but not its distribution with respect to time. The
SCS runoff equation is therefore a method of estimating direct runoff from 24-hour or 1-day storm
rainfall. The equation is:
P−Ia 2
� = P−Ia +S
Where: Q = accumulated direct runoff, mm
P = accumulated rainfall (potential maximum runoff), mm
Ia = initial abstraction including surface storage, interception, and infiltration prior
to runoff, mm
S = potential maximum retention, mm
The relationship between Ia and S was developed from experimental catchment area data.It
removes the necessity for estimating Ia for common usage.
The empirical relationship used in the SCS runoff equation is:
Ia = 0.2*S
Substituting 0.2*S for Ia, the SCS rainfall-runoff equation becomes:
�=
25400
� − �. � ∗ � �
� + �. � ∗ �
S = CN−254 S is related to the soil and cover conditions of the catchment area through the CN. CN
has a range of 0 to 100, and S is related to CN by:
IV.
Runoff Factors
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Runoff is rainfall excess or effective rainfall - the amount by which rainfall exceeds the capability of
the land to infiltrate or otherwise retain the rainwater. The principal physical catchment area
characteristics affecting the relationship between rainfall and runoff are land use, land treatment,
soil types, and land slope.
a)
Land Use
Land use is the catchment area cover, and it includes both agricultural and non-agricultural uses.
Items such as type of vegetation, water surfaces, roads, roofs, etc. are all part of the land use.
Land treatment applies mainly to agricultural land use, and it includes mechanical practices such
as contouring or terracing and management practices such as rotation of crops.
The SCS uses a combination of soil conditions and land-use (ground cover) to assign a runoff
factor to an area. These runoff factors, called runoff curve numbers (CN), indicate the runoff
potential of an area. The higher the CN, the higher is the runoff potential.
b)
Hydrologic Soil Groups
Soil properties influence the relationship between rainfall and runoff by affecting the rate of
infiltration. The SCS has divided soils into four hydrologic soil groups based on infiltration rates
(Groups A, B, C, and D). These shall be given to the effects of urbanization on the natural
hydrologic soil group. If heavy equipment can be expected to compact the soil during construction
or if grading will mix the surface and subsurface soils, appropriate changes shall be made in the
soil group selected. Also, runoff curve numbers vary with the antecedent soil moisture conditions,
defined as the amount of rainfall occurring in a selected period preceding a given storm. In general,
the greater the antecedent rainfall, the more direct runoff there is from a given storm. A five-day
period is used as the minimum for estimating antecedent moisture conditions. For this particular
section of the project the soil type lies under hydrological soil group B.
c)
Runoff Curve Numbers
The ERA Design Manual gives a series of tables related to runoff factors. The tables are based on
an average antecedent moisture condition, i.e., soils that are neither very wet nor very dry when
the design storm begins. Curve numbers shall be selected only after a field inspection of the
catchment area and a review of cover type and soil maps. Care shall be taken in the selection of
curve numbers (CN's). Use a representative average curve number, CN, for the catchment area.
Selection of overly conservative CN’s will result in the estimation of excessively high runoff and
consequently excessively costly drainage structures. Selection of conservatively high values for all
runoff variables results in compounding the runoff estimation. It is better to use average values and
design for a longer storm frequency.
The main catchment’s characteristics considered in determining its CN are:
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
Hydrological Soil Properties

Land cover properties (including land use, its treatment and hydrological condition)

The soils in the catchment relative wetness or dryness just prior to the rainfall event.
The potential maximum soil water retention, S, is related to hydrologic soil properties, land cover
and management conditions as well as, the soil moisture status of the Catchment prior to rainfall
event and expressed by a dimensionless response index termed the catchment curve number (CN)
The CN and S are related as follows:
S
25400
 254
CN
The CN number is selected according to soil type, moisture condition and land cover/use of the
watershed area.
A. Ia/p Parameter
Ia/p is a parameter that is necessary to estimate peak discharge rates. Ia denotes the initial
abstraction and p is the 24-hour rainfall depth for a selected return period. The 24-rainfall depth is
taken from the frequency analysis result found in section 2.4. For a given 24-hour rainfall
distribution Ia/P represents the fraction of rainfall that must occur before runoff begins.
B. Peak Discharge Estimation
The following equation were used for the estimation of the peak discharge in SCS method
qp =qu*A*Q
Where qp = peak discharge, m3/s
qu = unit peak discharge, m3/s/km2/mm
A = drainage area, Km2
Q = depth of runoff, mm
The unit peak discharge is obtained from the following equation, which requires the time of
concentration (tc) in hours and the initial abstraction rainfall (Ia/p) ration as input:
qu = ∝∗ ����+�������+�� �����
�
Where Co, C1 and C2 = regression coefficients given in table 2-9 for various Ia/p ratios:
conversion factor equal to 0.000431 in SI unit.
Table 4- 10: Coefficients for SCS Peak Discharge Method
Rainfall Type
Ia/P
C0
C1
C2
I
0.1
2.3055
-0.51429
-0.1175
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Rainfall Type
IA
II
III
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Ia/P
C0
C1
C2
0.2
2.23537
-0.50387
-0.08929
0.25
2.18219
-0.48488
-0.06589
0.3
2.10624
-0.45695
-0.02835
0.35
2.00303
-0.40769
0.01983
0.4
1.87733
-0.32274
0.05754
0.45
1.76312
-0.15644
0.00453
0.5
1.67889
-0.0693
0
0.1
2.0325
-0.31583
-0.13748
0.2
1.91978
-0.28215
-0.0702
0.25
1.83842
-0.25543
-0.02597
0.3
1.72657
-0.19826
0.02633
0.5
1.63417
-0.091
0
0.1
2.55323
-0.61512
-0.16403
0.3
2.46532
-0.62257
-0.11657
0.35
2.41896
-0.61594
-0.0882
0.4
2.36409
-0.59857
-0.05621
0.45
2.29238
-0.57005
-0.02281
0.5
2.20282
-0.51599
-0.01259
0.1
2.47317
-0.51848
-0.17083
0.3
2.39628
-0.51202
-0.13245
0.35
2.35477
-0.49735
-0.11985
0.4
2.30726
-0.46541
-0.11094
0.45
2.24876
-0.41314
-0.11508
0.5
2.17772
-0.36803
-0.09525
As per the physiographic and climate data of delineated watershed area of the project area
catchment area are large greater than 65km2 a peak discharge has been computed using HEC
1/SCS method with WMS software. Representative HEC-1/SCS analysis for major river
watersheds are as demonstrated in the section below with design rainfalls for rainfall region A4 is
used for the peak discharge computation to Muztera Tcc and Kebte tera is as detailed below;
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Figure 4- 8: Muztera Tcc @ 0+378 Delineated Watershed Area and Drainage Pattern
Figure 4- 9: Hydrograph for Muztera Tcc @ 0+378
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Figure 4- 10: Kebte Tera Chiro wereda @ 1+020 Delineated Watershed Area and Drainage Pattern
Figure 4- 11: Hydrograph for Kebte Tera Chiro wereda @ 1+020
The computation sheet of hydrological design /peak flood computation using SCS method is
presented in the Appendix.
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4.6
Hydraulic Design
4.6.1
General
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In the previous chapter, the runoff of the catchment area is determined. The next step is to provide
adequate, economical and sustainable drainage system that suite the site conditions for design
discharge.
Making the road corridor drainable enough to the extent possible and keep the road from flood and
its detrimental effect is the fundamental principle for highway drainage design & development of
Chiro Town internal Asphalt Road project. Evaluating existing drainage system/ environment and
formulating improved drainage system without creating additional load or stress to existing
condition is the main approach on drainage management improvement of the project. Hydraulic
assessment and design have been undertaken mainly based on peak discharge estimates from
hydrological analysis and geometric data obtained from ground survey of project corridor. Apart
from these, detail hydraulic design of drainage structures more importantly considers physical
prevailing hydraulic conditions as realized from detail onsite survey complemented by elder’s
historical drainage related information.
Pipe and slab/ box culvert and bridge under cross drainage structures, side ditch and flow
conveying channel on longitudinal flow conveying structures category have been identified and
designed to impart good surface drainage system of the road. Outlet side flow guide ditch also
provided to convey the runoff with improved hydraulic features till appropriate disposal point.
Embankment/ fill requirement of the road is determined based on onsite overland flow and
floodplain flow desk and physical assessment findings.
Roadside drainage facility of appropriate type and size has been designed to collect runoff
generated from road surface on urban areas and inlet side flow guide ditch to direct overland and
dispersed flow towards proposed structure. Outlet side channelization and flow guide works are
also recommended to improve hydraulic efficiency of the proposed structures.
4.6.2
Hydraulic Design Standard
The chief aim of this task was to determine the opening sizes of the drainage structures from the
rate of flood runoff (discharge) and the volume of runoff that will pass through the bridge.
This method deploys the hydraulic characteristics of the stream influencing the maximum
discharge, such as velocity of flow, slope of the stream, cross sectional area of the stream and
shape and roughness of the stream. This method will be used for major streams to compute the
design flood levels at crossing sites after the design discharges have been estimated by the
hydrological methods of either the SCS Unit Hydrograph Method and compared with the observed
flood marks. Cross-Sections of the crossing sites are being determined by the survey.
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4.6.3
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Manning’s Formula of Hydraulic Analysis
This method deploys the hydraulic characteristics of the stream influencing the maximum
discharge, such as velocity of flow, slope of the stream, cross sectional area of the stream and
shape and roughness of the stream. This method is used for the design flood levels at crossing
sites after the design discharges have been estimated by the hydrological methods of the SCS Unit
Hydrograph Method. Cross-Sections of the crossing sites have been determined by the survey.
Accordingly, the following Manning’s equation is used for high-water computations:
�
�
Where:
4.6.4
�
� = � ∗ �� ∗ �� ∗ �
Q
=
Discharge in [m3/sec]
R
=
Hydraulic mean depth [m] = A/P
A
=
Cross-sectional flow area [m2]
P
=
Wetted perimeter [m]
S
=
Longitudinal bed slope [%]
n
=
Manning’s roughness coefficient
Culvert and Auxiliary Facility Hydraulic Design
Drainage structures hydraulic sizing has been made both to small and relatively larger streams
deserving culverts on the proposed alignment. FHWA HY 8.7 advanced culvert hydraulic design
software have been used for culvert hydraulic evaluation and sizing purpose. As indicated on the
Employer’s requirement, all minor drainage structures (if any) shall be replaced by new ones of
minimum size 1220mm diameter.
Culvert hydraulic design criteria defined on the employer’s requirement (minimum size 1220mm,
HW/D ration 1.5 and outlet treatment) has been considered.
Three major drainage management systems have been adopted in the stretch of the road under
consideration using culvert structures:

Side collected flow relief culvert mainly in town sections

Defined flow from relatively larger and small sheets conveying culvert to
downstream side crossing the road

Plain and flood plain section generated flow (widely spread and shallow depth)
disposal structures.
The rule of thumb when installing a culvert is that natural channel modifications should be
minimized and that any constriction of the channel flow width must be avoided. This can be done
by maintaining the natural grade and alignment of the channel through the culvert. Depending
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upon flow type and pattern, hydraulic design approach adopted for culvert vary according to the
case. Single culvert design approach mostly for defined flow condition and multiple structure
hydraulic design approach for wide plain and floodplain section considering as a single
hydraulically serving unit adopted in the project. Sample culvert hydraulic design to each case is
demonstrated on subsequent section.
4.6.5
Pipe Culverts
The pipe culvert culverts were designed using hy-8software and design nomograph for the HW/D
of 1.2 though the manual allows to HW/D of 1.5. Besides,
Figure 4- 12: Design Nomograph for the Concrete Pipe Design
From the above the nomograph, the capacities of

Concrete Pipe with 1.22m diameter is 3.0m3/s for HW/D =1.20 (HW=1.59m)

Concrete Pipe with 1.06m diameter is 2.0m3/s for HW/D =1.20 (HW=1.27m) and

Concrete Pipe with 0.91m diameter is 1.23m3/s for HW/D =1.20 (HW=1.10m)
Single or double pipe culverts were proposed depending on the magnitude of estimated discharge.
Inlets and outlets of culverts will have paved waterways, as per ERA standard, for protecting scour
of foundation materials. The end walls will be determined in consideration of type and direction of
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flow among the possible alternatives of ERA standard. Furthermore, a check for exit velocities and
scour-ability of the streambed will be undertaken.
From total of all road segment there are 54 crossing structure are proposed pipe culvert
4.6.6
Slab/box Culverts
. The hydraulic opening size determination has been carried out using both trial and error
procedure and HY8 computer modelling. The hydraulic analysis and design output of major
culverts using HY8 is shown in the figures below. The summery of hydraulic analyses of slab and
box culvert is presented under annex-part.
From total of all road segment there are 12 crossing structure are proposed Slab culvert.
The hydraulic analysis of slab culverts at each station were presented in appendix
Sample HY-8 Software output
Table 4- 11: Input of hydraulic data for HY8 from Hundi Gudina Scl Nejebac Kidane Mihret @km
2+060
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Figure 4- 13: HY-8 hydraulic analysis output result along the culvert at station 2+060
Summary table result of the proposed culvert capacity including fill height
As shown from the above hy-8 output the size of 3.0m X 2.5m Slab/Box culvert is only overtopped
beyond 20.79m3/s but design discharge is 13.47m3/s hence, it is clearly safe.
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The same method of HY-8 calculation execution is used for others proposed crossing slab/box
culverts.
4.6.7
Design of Major Cross Drainage Structures
Bridges and multiple cell box or slab culverts having a total span of greater than 6m are
categorized under major drainage structures. However, in this section discus about only major
drainage structure Bridge. The following are the criteria related to the hydraulic analyses for the
sufficiency of the bridge.
Location: The location of major crossing structures should be selected in such a way that there
exit minimum span with suitable foundation and having straight reach of stream. The foundation
should have preferably strong (naturally sound rock) bearing capacity and less scourablity to
minimize the overall cost of the structure.
Design Floods: For purposes of the evaluation of backwater (afflux), clearance, and overtopping,
design floods have been established.
Backwater: Backwater and/or increases over existing condition up to 0.5 m during the passage of
the design flood, if practicable. Further, backwater shall not significantly increase flood damage to
property upstream of the crossing.
Clearance: A minimum clearance conforming to the requirements of the Bridge Design manual
shall be provided between the design approach water surface elevation and the low chord (soffit)
of the bridge to allow for passage of debris. Clearance (free board) will be according to ERA’s
Bridge Design Manual whose values are as stated below.
Table 4- 12: Free board recommendation as per ERA DDM
Discharge, Q (m3/s)
Freeboard (m)
0 – 3.0
0.3
3.0 -30
0.6
30 -300
0.9
> 300.0
1.2
Depending on the availability of sufficient data, hydraulic design and analysis of major drainage
structures can be carried out by simple spread sheet analysis of Manning’s equation as well as
hydraulic modelling software like HEC-RAS.
Manning’s equation has been used for developing the rating curve at major cross drainage
structures.
2
1
1
Q   A R 3  S 2
n
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Where: -
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Q = Discharge in m3/s
n
= weighted manning’s roughness coefficient
R
= hydraulic radius (m)
S
= Slope of energy grade line or channel bed slope (m/m)
After developing the stage discharge curve, the peak design discharge is used to locate the High
Flood Mark (HFM). The effect of Back water is considered for all cases. The normal water level
which corresponds to flood with corresponding return period has been taken as High-Water Mark
(HWM). The waterway (opening area) at the bridge is designed taking into account the backwater
effect due to constriction and scour.
A spread sheet computation using HEC-RAS modelling in the principle of manning equation were
used for checking the hydraulic adequacy of existing structures as well as for hydraulic opening
size analysis and design of newly proposed bridges. From total of all road segment there are 5
crossing structure are proposed bridges Structures, proposed and the HEC-RAS output of the
bridge is shown below.
Bridge at Hundi Gudina Scl Nejebac Kidane Mihret 0+418Km
For bridge site located at 0+418km, survey data has been collected and HEC RAS model has
been run considering discharge load as shown below:
Design discharge =136.5m3/s
Figure 4- 14: HEC-RAS Output after addining Bridge waterprofile
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Station@0+418 the propose bridge size 10m span by 4m clear height.
Therefore, for defined span and clear height arrangement mainly considered from onsite physical
survey and preliminary desk modelling, HEC RAS model has been run and evaluated for
potential backwater effect
4.6.8
Design of Longitudinal Drainage Facility
A roadside ditch is defined as an open channel paralleling the highway embankment within the
limits of the highway right-of-way. Its primary function is to collect runoff from the highway and
areas adjacent to the right-of-way and to transport this accumulated water to an acceptable outlet
point. A secondary function of a roadside ditch is to drain the base of the roadway to prevent
saturation and loss of support for the pavement.
Side ditches will be designed to carry the storm water run-off originating from the carriageway,
shoulder, drain and cut/back slope as well as channelized streams. The design of side ditch shall
be undertaken to ensure that no overtopping will occur.
The expected flow, run-off, will be estimated using the following formula:
Q=1/360(C x I x A)
Where: Q
the expected flow (m3/s)
C
the runoff coefficient
I
the intensity of rainfall (mm/hr)
A
the area drained (hectares)
2
Q  K  A R 3  S
1
2
 A V
2
1
V  KR 3 S 2
The capacity of side ditch will be estimated using Manning Striker formula (metric):
Where:Q
Capacity of ditch (m3/s)
A
cross sectional area of water (m2)
V
velocity of flow (m/s)
K
roughness coefficient (Table 3.3)
R
hydraulic radius (A/P where P is the wetted perimeter)
S
longitudinal slope (m/m)
Limiting values for the velocity of flow (V) to prevent scour, together with the corresponding
roughness coefficients are given in table below.
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Table 4- 13: Roughness coefficients and Maximum permissible velocity
Max.
Ditch material
Permissible Roughness
velocity (m/s)
coefficient
Sand, loam, fine gravel, volcanic ash
0.6
45
Stiff clay
1.1
50
Coarse gravel
1.5
40
Conglomerate hard shale, soft rock
2.0
25
Hard rock
5.0
25
Masonry
5.0
40
Concrete
10.0
60
The introduction of erosion protective measures such as check dams and ditch lining in all places
where the velocity of water exceeds the maximum permissible velocity for the corresponding ditch
material given in table 3-2 above would be very expensive for the specific class of roads.
Therefore, for these

In places where the velocity of water in the ditch exceeds 10 m/s., check dams in
addition to ditch lining is required in order to reduce the speed of water.

Wherever the velocity of water in the ditch is between 3.0 – 5.0 m/sec. dry masonry
check dams as per the standard given in the detailed engineering design to be
introduced.
Depending on the topographic feature and location (rural/ urban) of the proposed road alignment,
the following provisions can be adopted and can modified and amended based on local situations.
A.
Flat Areas
In flat areas drains are required for the following conditions:
 Cut section
 Embankment height is less than 1m.
 Embankment height is more than 1m but the surrounding ground is falling
towards the project road
The side drains in the flat areas of the triangular unlined type. the depth is kept at a minimum of
0.50 m and the side slopes are 1 vertical to 2 horizontals. However, in the expansive soils areas,
the trapezoidal, unlined drains have been replaced with lined drains (of the type used in the rolling
areas) The bottom of the drain is 0.5 m wide, to prevent the exchange of moisture with the deeper
layers of soils and in town section the rectangular ditch with lined with appropriate dimension
based on discharge is proposed.
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B.
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Rolling Areas
The drains to be used in the rolling areas could be trapezoidal lined type depending on the
longitudinal grade of the road and sub-grade material extension. The bottom of the drain is 0.5 m
wide; the side slops depend on the embankment side slope of the road. The depth of the drain is
kept to a minimum of 0.50 m.
C.
Mountainous and Escarpment Areas
The drains to be used in the mountainous and very steep areas are of the rectangular / trapezoidal
lined type with minimum bottom width and depth of 0.5 m and 0.5m respectively depending on the
longitudinal grade of the road and sub-grade material extension. The side slops depend on the
embankment side slope of the road.
D.
Urban Areas
The design of a drainage system for a carriageway traversing an urbanized region is generally a
more complex problem than for carriageways traversing sparsely settled rural areas. This is often
due to:
 The wide carriageway sections, flat grades, both in longitudinal and transverse
directions, shallow water courses, absence of side channels;
 The more costly property damages which may occur from ponding of water or from
flow of water through built-up areas;
 The fact that the carriageway section must carry traffic, but also act as a channel to
convey the water to a disposal point. Unless proper precautions are taken, this flow
of water along the carriageway will interfere with or possibly halt the passage of
highway traffic.
The drains to be used in the urban areas are of the rectangular lined type or pipe culvert where
relevant. To evacuate runoff drainage from the pavement curb inlets are proposed at every 20-25
m. Based on the above description and as per ERA DDM 2013 recommendation,
It recommends new ditch and the size of ditch proposed depend on catchment discharge, but the
shape of the ditch mainly governing by considering urban, Rural, Soil extension of the project and
Discharge, although the ditch type whether lined or unlined depend on Urban/Rural, topography
and soil type. Others stretch of the side ditch design the same concept and some procedure from
the above,
4.6.9
Bridge Scouring
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The intensity and extent of scouring effect on major drainage structure crossings are a paramount
importance for the safety and sustainability of the highway projects. Hence through understanding
and investigation of scouring effect discussed as follows.
Scour computation is based on ERA Drainage Design Manual and based on the reference
“Evaluating Scour at Bridges, Fourth Edition (US, National Highway Institute (NHI))”
Scour is the result of the erosive action of flowing water, excavating and carrying away material
from the bed and banks of streams. Different materials scour at different rates. Loose granular
soils are rapidly eroded by flowing water, while cohesive or cemented soils are more scour
resistant. However, ultimate scour in cohesive or cemented soils can be as deep as scour in sandbed streams. Under constant flow conditions, scour will reach maximum depth in sand and gravel
bed materials in hours; cohesive bed materials in days; glacial tills, sand stones and shale in
months; limestone in years and dense granites in centuries. Under flow conditions more typical of
actual bridge crossings, several floods will be needed to attain maximum scour.
A factor in scour at highway crossings and encroachments is whether the scour is clear-water or
live-bed scour. Clear–water scour occurs where there is no transport of bed material upstream of
the crossing or encroachment and live-bed scour occurs where there is transport of bed materials
from the upstream reach into the crossing or encroachment.
Total scour at a highway crossing is comprised of three components.

Long-term aggradations and degradation,

Contraction scour and

Local scour (due to pier and abutment)
4.6.10 Back water effect (Afflux)
The intensity and extent of scouring and backwater effect on major drainage structure crossings
are a paramount importance for the safety and sustainability of the highway projects. Hence
through understanding and investigation of scouring and backwater effect discussed as follows.
The restriction to free water flow due to piers and abutment causes the head of water to rise on the
upstream side of the structure. The water level downstream may also be lowered and the velocity
increases. It is necessary to estimate the rise of water level on the approach side to ensure that the
river banks will not be breached where overflowing flood water would cause damage, and to check
that the desired clearance for floating debris or river traffic is maintained below the superstructure.
The magnitude of backwater can be affected by the shape of the river bed, its eccentricity, scour
holes and related factors. The shape of the bridge works also influences the magnitude of back
water effect, i.e. by any skew, river training, embankments and relief culverts.
configuration, a good estimate may be made using the formula below:
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h 
Where:h
=
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
V2  W2
 2 2  1 
2g  c L

afflux
V
=
average velocity of flow [m/sec]
g
=
acceleration due to gravity [9.8 m/sec2]
W
=
unobstructed width of the stream [m]
L
=
linear water way of the bridge opening less obstruction width, if any [m]
C
=
coefficient of discharge through the bridge, taken as 0.7 for sharp entry and 0.9
for bell mouthed entry.
4.7
Conclusions and recommendations
A total of 71 cross drainage structures have been designed and evaluated on section of the road
from of the projects where 5 structure considered as bridge, 54 pipe culverts and the remaining
12as slab/ box structures.
The life of roads and utilities depend on the drainage system installed at appropriate locations.
With this regard an economical and sustainable drainage system has been studied and proposed
for the section of the road alignment. As we have discussed and presented trough out this report
the proposed road alignment traversing on a predominately Rolling and mountainous terrain, since,
there are number of small and large crossing structures to be constructed to prevent standing
water and overlapping.
Making the road corridor drainable enough is the main drainage objective of the project addressing
both hydrological analysis and hydraulic designs.
From physical drainage assessment and detail desk analysis, it has been realized that defined
sheet flows, overland and concentrated floodplain flows are the major drainage features of the
project deserving management option appropriate to it. Defined streams/ sheets flow
accommodating facility design, overland flow guide
It has been believed that drainage design substantially addresses project hydrological and
hydraulic problems at draft level but due drainage inter-related features unforeseen features may
prevail to existing indicating subsequent inspection, correction and implementation works both at
desk and site level.
From project specific features related to drainage, overall project safety and sustainability not only
depends on the intervention made by contractor rather the local community and administration
should take a part on land, localized drainage management and flood protections works. In this
regard, the Oromia roads and logistic bureau and employer’s representative are advised to play a
vital role in cooperating all parties and building project ownership.
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5
GEOMETRIC DESIGN
5.1
Introduction
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The overall process of the road alignment (horizontal and vertical) design in different terrain
condition to meet the need of the road users is generally known as geometric design. The main
geometric features are:
 The horizontal alignment;
 Vertical alignment; and
 Road Cross Section
Besides these main features, geometric design involves design of road furniture and safety
enhancing structures and elements
The process of geometric design usually encompasses design considerations resulting from multidisciplinary studies which try to define the various contexts of the project road. Accordingly,
geometric design has to be carried out in a context sensitive manner. Context Sensitive Design is a
collaborative, interdisciplinary approach that involves all constituents to develop a transportation
facility that fits its physical setting and preserves scenic, aesthetic, historic and environmental
resources, while maintaining safety and mobility to all road users, and enhancing the economic,
social and other needs of the society.
In terms of this concept, it is assumed that every project is unique which requires designers to
address the needed roadway improvements while safely integrating the design into the unique
surrounding natural and built environment.
Thus, geometric design must aim at combining various geometric design elements to produce a
sound and harmonious design which
 Provide the simplest geometry attainable, consistent with the physical constraints,
 Provide a design that has a reasonable and consistent margin of safety at the expected
design speeds,
 Provide a facility that is adequate and convenient to all the road users at the expected
traffic conditions,
 Provide a facility that is Stable and Sustainable
 Provide a facility that is in harmony with the community and preserves environmental,
scenic, aesthetic, historic, and built and natural resources of the area.
 Provide a facility that has acceptable economic returns
The hallmark of professionalism in geometric design is the ability to foresee and optimize the
contrasting objectives that are inherent in any geometric design project outlined above. Good
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highway design is the art of combining and balancing the various controls in a perceptive fashion
and is not merely an exercise in three dimensional geometrics. These different objectives of road
engineering should be prioritized initially according to their importance to the specific project. For
instance, a section of high standard road that has to pass through a deep reserved forest may
have to be designed to the lowest design standard possible to minimize negative impacts to the
forest.
Geometric design standards often define parameters and limiting values considering the following
three main objectives:  it shall ensure safety and comfort of drivers;
 it shall ensure that the road is designed economically; and
 it must ensure uniformity of the alignment
In line with what is stated above, geometric design standards often try to define acceptable and
economical level of service, and margin of safety with limited emphasis on roadway aesthetics for
the particular design standard. However, they barely define acceptable level of stability, social and
environmental returns and impacts. So, often compromising geometric design standards to fulfil
these other important objectives of highway design in an optimal manner is imperative.
These geometric elements have important bearing on how the road will function, its capacity, driver
behaviour and safety. The traditional approach in geometric design considers the three views of
layout plan, longitudinal section and cross-section. The road user sees the road as a constantly
changing continuum as he drives along, and the appearance of the road influences the driver's
behaviour. It is therefore important to provide the motorist with reasonable clues as which provide
guide and inform him as to what to expect as he drives along the road; such clues should be clear
messages, which are unlikely to mislead him.
Applying standard and practice without considering the prevailing circumstances is no substitute
for judgment, and brings no assurance of acceptable end product. Equally, design prepared
without referring to general accepted standard and practice are not likely to serve the travelling
public as intended. Design based on a combination of sound professional judgment, applicable
standards and current practices will generate the most effective road.
It is also good to note that standards usually give guidance whenever the terrain and other
associated factors are in favour of the selected geometric design standard. Nowadays the name
“manual” is being replaced with “Guide to”. This manifest that “manuals” are sensed as more
restricting to the designer to use his judgment and experience. The purpose of this replacement is
thus to give the designer more space and flexibility to arrive at balanced design in reconciliation of
the different contrasting objectives of road facilities. Therefore, the geometric design standards
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summarized in ERA manual should be intended to provide guidance for designers rather than to be
considered as rigid minima.
Departures from standard made to produce optimized design with varying level of compromise
among the contrasting multi-objectives of highway facilities including safety, stability, serviceability,
economy, environmental and social compatibility, and practicality of the design for construction and
maintenance are therefore often required especially in roadways that traverse through difficult
terrain conditions and sensitive social and environmental areas.
With these considerations in mind, the consultant team of experts has carried out detailed
assessment of the project road corridor which is mostly new and partly existing alignment and
geometric design standards have been established.
The designer has attempted to provide an appropriate design standard that confirms to the existing
road terrain condition and combinations of these elements should be defined in relation to the
following controls factors:
 Topography and land use
 Road function
 Traffic volume
 Design vehicle and vehicle characteristics
 Design speed and other speed controls
 Road safety considerations
 Environmental considerations
 Economic and financial considerations
Thus the Consultant has emphasized and attempted to arrive at a final design, which:
 Fits into the existing natural condition, terrain by making a balance with the physical and
social environment,
 Fulfils the projected traffic requirements, and
 Encourages consistency and uniformity of operation.
 Is economical for implementation
 Has a reasonable and consistent margin of safety at the expected design speeds,
 Is adequate and convenient to all the road users at the expected traffic conditions,
 Is in harmony with the community and preserves environmental, scenic, aesthetic, historic,
and built and natural resources of the area.
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5.2
Design Control and Criteria
5.2.1
Functional Classification
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Road function is basically related to the most common types and purposes of travel, trip and
character of service the roads provide. The character of service can broadly be understood as
mobility, access and a mixture of Mobility and Access.
In the Ethiopian context road classification is based on the function of the road it serves. In line
with this the Ethiopian Roads Authority Geometric Design Standard Manual, 2013, has classified
the existing roads based on the function they serve. It has also set terms on which future road
classification should base.
Functional classification (the grouping of highways by the character of service they provide) of
roads was developed mainly for transportation planning purposes. ERA’S Design Standard
classifies roads into five (5) categories based on the character of service they provide. These are
 Trunk Roads
 Link Roads
 Main Access Roads
 Collector Roads
 Feeder Roads
As the main purpose of the project road is to mainly provide access to the society chiro incorporate
9 Road Segments. However, Chiro Town Internal Asphalt project is an urban road project hence
the road functional classification shall better be by urban city road class. Table below shows the
classification.
Table 5- 1: Road segment class and road width
Road
Segment
Description
Road
Total Road
Class
Way Width
1
Muz tera –TTC-Qilisa
SAS
20
2
Kebt tera-Chiro Wereda Office SAS
20
3
Sumeya Bridge-Addis Ketema
CS
10
CS
15
Center-ODA CS
15
4
5
Agape
Hotel-Agri
Center-TTC
Agri
Reserch
Reserch
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Mixed
30
Residential/
30
commercial
Residential/
30
commercial
Residential/
30
commercial
Residential/
30
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Road
Segment
Description
Road
Total Road
Class
Way Width
Bultu University-Main Asphalt
Chiro Town Administration-
6
20
CS
15
CS
10
CS
15
Chiro Wereda Office – Care CS
10
Hundi
7
Gudina
Scl-Nejebac
Kidane Mihret
Hundi Gudina Scl-Aschalew
8
Hotel
Blood
9
Bank-Gende
Bono
10
Kuteba
Design
Key Context
Speed (km/h)
commercial
CS
Mtichu-Leila
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Ethiopia
Mixed
30
Mixed
30
Residential
30
Residential/Partly
Commercial
Residential/Partly
30
30
Commercial
ERA Geometric design parameters for design standard DC6 is adopted for the project road.
5.2.2
Geometric Classification
ERA Geometric classification of roads known as design standards of roads classifies roads by the
design Annual Average Daily Traffic (AADT) of the road. This geometric class is then associated
with design speed depending on terrain and urbanization of the area, which links the geometric
characteristics of the road with its function, the physical conditions of the area and the environment.
According to ERA Geometric Design Manual, various factors influence selection of road geometric
standard. The most notable ones are: function of the road, volume of traffic, terrain through which
the road traverses, road safety, and economy.
Roads standards are mainly selected based on the road’s intended capacity to accommodate
traffic. Accordingly, for high traffic volumes a higher design standard road should be provided (i.e.,
wider carriageways, gentle curves, flatter vertical gradient, full overtaking distances etc.) while the
opposite is true for low traffic.
The function of the road is determined by the character and anticipated level of service that the
road would deliver. Typically, this relates to functional classification of the road for which a generic
definition is given (based on the standard under consideration) indicating its primary function and
purpose.
It is also understood that the improvement of road standards (e.g. upgrading of pavement surface,
wider carriageway, higher speed, better sight distance etc.) would reduce the rates of accidents.
However, this may not be necessarily true and in effect may increase accident rates on the
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contrary. This is due to the fact that accidents have higher degree of dependence on road user
behaviour, vehicle condition as well as vehicle speeds etc. Therefore, in adopting a certain
geometric design standard, these factors (including others) are taken into consideration implicitly
within the standards.
Among various parameters, selection of geometric design standard should consider the alignment
constraints imposed by the terrain, and recommend appropriate design speed to be adopted for
particular sections. Appropriate typical cross sections shall also be used for rural, urban, and periurban and for the different terrain conditions.
The other most important factor is the economic feasibility of the project road; that the benefits of
the road to the society and the country as a whole would compensate for the construction,
maintenance, vehicle operation and other costs of the project road. A higher design standard road
on the basis of the project traffic volume, road function and terrain having unacceptable economic
rate of return may sometimes be avoided and in place of it the project road may need to be
designed for a lower geometric standard road thereby the overall costs could decrease and the
road becomes economical with acceptable economic rate of return.
5.2.3
Traffic Volume and Characteristics
Road standards are also selected based on the road’s intended capacity to accommodate traffic.
Normally, for high traffic volumes a higher set of design standard (i.e. wider carriageways, gentle
curves, flatter vertical gradient, full overtaking distances etc.) are anticipated while the vice versa is
true for low traffic.
A traffic count on the proposed project road, Chiro Town Internal Asphalt Road Project road was
conducted because the project road is accessible for the traffic as well there are very limited trip
generating frequency from the origins and destination specially related to the agricultural
investments lands. Therefore, the consultant estimates the project traffic from the developmental
generate traffic.
After developmental data are collected, detail data calculation and analysis is carried out to arrive
at the Annual Average Daily Traffic (AADT) that will use the proposed road up on completion of its
construction.
To determine the design AADT, the determination or selection of the design life of the project road
has been determined.
 Design Life
The approach recommended for estimating the traffic for geometric design purpose is based on the
estimated traffic level at the mid-year of the design life and this therefore requires an estimate of
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the traffic growth rate. This method eliminates the risk of under design that may occur if the initial
traffic is used and the risk of over design if traffic at the end of the design life is used. A design life
of 15 to 20 years is recommended for paved roads and 20 years for paved roads.
Based on the ERA Pavement Design Manual 2013, the determination of the design period should
consider different factors such as Functional importance of the road, Traffic volume, Location and
terrain of the project, financial constraints and difficulty in forecasting traffic. The manual provides
the general guide line for selecting the design period as shown in the table below.
Table 5- 2: Road functional Classification verses Design Period
Road Classification
Design Period (years)
Trunk Road
20
Link Road
20
Main Access Road
15
Other Roads
10
For the subject project since it is considered as urban city road class a design period of 20 years
from the year the road is opened to traffic i.e. (2028- 2047) is considered for geometric design. The
project road is expected to be opened to traffic in the year 2028.
 Traffic Forecasting and AADT
Traffic projection has been made for 20 consecutive years of the design period by applying the
growth rates estimated above. The following table gives the forecasted traffic during the design
period of the project. The summary of the traffic forecast is shown in tables below.
Table 5- 3: Traffic forecast of road segment 6 and 7 at station 1 for the years 2028– 2047
Road segment 6 and 7
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus S/Truck
M/Truck H/Truck Track Trailer
Total Sum
2028
670
131
8
7
1
14
8
7
0
845
2029
729
142
9
7
1
16
9
7
0
920
2030
793
155
10
8
1
17
10
8
0
1001
2031
863
168
10
8
1
19
11
9
0
1089
2032
939
183
11
9
1
20
12
9
0
1185
2033
1,022
199
12
10
1
22
13
10
0
1290
2034
1,112
217
13
11
1
24
14
11
0
1403
2035
1,210
236
14
12
1
26
15
12
0
1527
Year
Goods Vehicles
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Road segment 6 and 7
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus S/Truck
M/Truck H/Truck Track Trailer
Total Sum
2036
1,316
257
16
13
2
29
17
13
0
1662
2037
1,432
279
17
14
2
31
18
14
0
1808
2038
1,559
304
19
15
2
34
20
16
0
1968
2039
1,696
331
20
16
2
37
22
17
0
2141
2040
1,845
360
22
18
2
40
23
19
0
2330
2041
2,008
392
24
19
2
44
26
20
0
2535
2042
2,185
426
26
21
3
48
28
22
0
2759
2043
2,377
464
28
23
3
52
30
24
0
3002
2044
2,587
505
31
25
3
57
33
26
0
3266
2045
2,815
549
33
27
3
62
36
29
0
3554
2046
3,063
598
36
29
4
68
39
31
0
3867
2047
3,332
650
39
32
4
74
43
34
0
4208
Year
Goods Vehicles
Source; consultant
Table 5- 4: Traffic forecast of road segment 2 at station 2 for the years 2028– 2047
Road segment 2 and 10
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus
S/Truck M/Truck
H/Truck Track Trailer
Total Sum
2028 2150
370
169
60
17
109
35
19
13
2939
2029 2,339
402
183
65
18
118
38
21
14
3198
2030 2,545
438
199
70
20
129
42
22
15
3480
2031 2,769
476
216
77
22
141
46
25
16
3787
2032 3,013
518
235
83
24
153
50
27
18
4120
2033 3,279
564
256
90
26
167
54
29
19
4483
2034 3,568
613
278
98
28
182
59
32
21
4878
2035 3,882
667
302
107
30
198
64
35
23
5308
2036 4,224
726
328
116
33
216
70
38
25
5776
2037 4,596
790
356
126
36
236
76
41
28
6285
2038 5,001
860
387
137
39
257
83
45
30
6839
2039 5,441
935
421
149
42
280
91
49
33
7441
2040 5,921
1,018
458
162
46
305
99
53
36
8097
2041 6,442
1,108
497
176
50
332
108
58
39
8810
Year
Goods Vehicles
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Road segment 2 and 10
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus
S/Truck M/Truck
H/Truck Track Trailer
Total Sum
2042 7,010
1,205
540
191
54
362
118
63
43
9586
2043 7,628
1,311
587
208
59
395
128
69
46
10431
2044 8,300
1,427
638
226
64
430
140
75
51
11350
2045 9,031
1,552
694
245
69
469
152
82
55
12350
2046 9,826
1,689
754
267
75
511
166
89
60
13438
2047 10,692
1,838
819
290
82
557
181
97
66
14622
Year
Goods Vehicles
Source; consultant
Table 5- 5: Traffic forecast of road segment 3 at station 2 for the years 2028– 2047
Road segment 3
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus
S/Truck M/Truck
H/Truck Track Trailer
Total Sum
2028 2150
370
169
60
17
54
18
9
6
2852
2029 2,339
402
183
65
18
59
19
10
7
3103
2030 2,545
438
199
70
20
64
21
11
7
3376
2031 2,769
476
216
77
22
70
23
12
8
3673
2032 3,013
518
235
83
24
77
25
13
9
3997
2033 3,279
564
256
90
26
83
27
15
10
4349
2034 3,568
613
278
98
28
91
30
16
11
4731
2035 3,882
667
302
107
30
99
32
17
12
5148
2036 4,224
726
328
116
33
108
35
19
13
5601
2037 4,596
790
356
126
36
118
38
21
14
6095
2038 5,001
860
387
137
39
128
42
22
15
6631
2039 5,441
935
421
149
42
140
45
24
16
7215
2040 5,921
1,018
458
162
46
152
49
27
18
7850
2041 6,442
1,108
497
176
50
166
54
29
20
8541
2042 7,010
1,205
540
191
54
181
59
32
21
9294
2043 7,628
1,311
587
208
59
197
64
34
23
10112
2044 8,300
1,427
638
226
64
215
70
38
25
11002
2045 9,031
1,552
694
245
69
234
76
41
28
11971
2046 9,826
1,689
754
267
75
256
83
45
30
13025
2047 10,692
1,838
819
290
82
279
90
49
33
14172
Year
Goods Vehicles
Source; consultant
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Table 5- 6: Traffic forecast of road segment 1-1 at station 2 for the years 2028– 2047
Road segment 1-1
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus
S/Truck M/Truck
H/Truck Track Trailer
Total Sum
2028 2465
491
207
74
18
78
32
21
7
3393
2029 2,682
534
225
81
19
85
35
23
7
3692
2030 2,919
581
245
88
21
93
38
25
8
4017
2031 3,176
632
266
96
23
101
41
28
8
4371
2032 3,456
688
289
104
25
111
45
30
9
4756
2033 3,760
748
314
113
27
120
49
33
10
5174
2034 4,091
814
341
123
29
131
53
36
11
5630
2035 4,452
886
371
133
32
143
58
39
12
6126
2036 4,844
964
403
145
35
156
63
42
13
6665
2037 5,271
1,049
438
157
38
170
69
46
14
7252
2038 5,735
1,141
476
171
41
185
75
50
16
7891
2039 6,241
1,242
517
186
45
202
82
55
17
8586
2040 6,790
1,351
562
202
48
220
89
60
19
9342
2041 7,389
1,470
611
220
53
240
97
65
20
10164
2042 8,039
1,600
664
239
57
261
106
71
22
11060
2043 8,748
1,741
722
259
62
285
116
78
24
12034
2044 9,518
1,894
784
282
68
310
126
85
26
13093
2045 10,357
2,061
852
306
74
338
137
92
29
14246
2046 11,269
2,242
926
333
80
369
150
100
31
15501
2047 12,262
2,440
1,007
362
87
402
163
109
34
16866
Year
Goods Vehicles
Source; consultant
Table 5- 7: Traffic forecast of road segment 1-2 at station 2 for the years 2028– 2047
Road segment 1-2
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus
S/Truck M/Truck
H/Truck Track Trailer
Total Sum
2028 3224
554
253
89
25
81
26
14
9
4278
2029 3,508
603
275
97
27
89
29
15
10
4654
2030 3,818
656
299
106
30
97
31
17
11
5064
2031 4,154
714
324
115
32
105
34
18
12
5510
2032 4,520
777
353
125
35
115
37
20
13
5995
Year
Goods Vehicles
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Road segment 1-2
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus
S/Truck M/Truck
H/Truck Track Trailer
Total Sum
2033 4,918
845
383
136
38
125
41
22
15
6523
2034 5,351
920
417
147
42
136
44
24
16
7097
2035 5,823
1,001
453
160
45
149
48
26
17
7722
2036 6,336
1,089
492
174
49
162
53
28
19
8402
2037 6,894
1,185
535
189
53
177
57
31
21
9142
2038 7,501
1,290
581
206
58
193
62
34
23
9947
2039 8,162
1,403
632
223
63
210
68
37
25
10822
2040 8,881
1,527
686
243
69
229
74
40
27
11775
2041 9,664
1,661
746
264
75
249
81
43
29
12812
2042 10,515
1,808
811
287
81
272
88
47
32
13940
2043 11,441
1,967
881
312
88
296
96
52
35
15168
2044 12,449
2,140
958
339
96
323
105
56
38
16503
2045 13,546
2,329
1,041
368
104
352
114
61
41
17956
2046 14,739
2,534
1,131
400
113
383
124
67
45
19537
2047 16,038
2,757
1,229
435
123
418
136
73
49
21258
Year
Goods Vehicles
Source; consultant
Table 5- 8: Traffic forecast of road segment 5 at station 3 for the years 2028– 2047
Road segment 5
Private Vehicles
Public Transport
Car
4WD
S/Bus
M/Bus
L/Bus
S/Truck
M/Truck
H/Truck
2028
673
185
88
53
18
49
51
2029
732
202
95
57
20
54
2030
796
219
103
62
22
2031
867
239
112
68
2032
943
260
122
2033
1,026
283
2034
1,116
2035
Year
Goods Vehicles
Track
Total
Trailer
Sum
0
0
1117
56
0
0
1215
58
61
0
0
1322
23
64
67
0
0
1439
73
25
69
73
0
0
1565
133
80
28
76
79
0
0
1703
307
144
87
30
82
86
0
0
1853
1,215
335
157
94
33
90
94
0
0
2017
2036
1,322
364
170
102
35
98
102
0
0
2194
2037
1,438
396
185
111
39
107
112
0
0
2387
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Road segment 5
Private Vehicles
Public Transport
Car
4WD
S/Bus
M/Bus
L/Bus
S/Truck
M/Truck
H/Truck
2038
1,565
431
201
121
42
116
122
2039
1,703
469
219
132
46
127
2040
1,853
510
238
143
49
2041
2,016
555
258
155
2042
2,194
604
281
2043
2,387
657
2044
2,597
2045
Year
Goods Vehicles
Track
Total
Trailer
Sum
0
0
2598
132
0
0
2827
138
144
0
0
3076
54
150
157
0
0
3346
169
58
164
172
0
0
3641
305
184
64
179
187
0
0
3962
715
332
199
69
195
204
0
0
4311
2,826
778
360
217
75
212
222
0
0
4691
2046
3,075
847
392
236
82
231
242
0
0
5104
2047
3,346
921
426
256
89
252
264
0
0
5553
Source; consultant
Table 5- 9: Traffic forecast of road segment 4, 8 and 9 at station 4 for the years 2028– 2047
Road segment 4,8 and 9 forecast @ station-4
Private
Vehicles
Public Transport
Car
4WD
S/Bus
M/Bus
L/Bus
S/Truck
M/Truck H/Truck
2028
631
242
77
30
2
48
28
2029
687
263
84
32
2
52
2030
748
286
91
35
2
2031
813
312
99
38
2032
885
339
107
2033
963
369
2034
1,048
2035
Year
Goods Vehicles
Track
Total
Trailer
Sum
24
0
1083
31
26
1
1178
57
34
28
1
1282
3
62
37
31
1
1395
41
3
68
40
33
1
1518
117
45
3
74
44
36
1
1651
402
127
49
3
81
48
40
1
1797
1,140
437
138
53
4
88
52
43
1
1955
2036
1,241
475
150
58
4
96
56
47
1
2128
2037
1,350
517
163
63
4
104
62
51
1
2315
2038
1,469
563
177
68
5
114
67
56
1
2519
2039
1,598
612
192
74
5
124
73
61
1
2741
2040
1,739
666
209
80
5
135
80
67
1
2983
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Road segment 4,8 and 9 forecast @ station-4
Private
Vehicles
Public Transport
Car
4WD
S/Bus
M/Bus
L/Bus
S/Truck
M/Truck H/Truck
2041
1,892
725
227
87
6
147
87
2042
2,059
789
247
95
6
161
2043
2,240
859
268
103
7
2044
2,438
934
292
112
2045
2,653
1,016
317
2046
2,886
1,106
2047
3,140
1,203
Year
Goods Vehicles
Track
Total
Trailer
Sum
73
1
3246
95
79
2
3532
175
103
86
2
3843
8
191
112
94
2
4182
122
8
208
123
102
2
4551
345
132
9
227
134
112
2
4952
374
144
10
247
146
122
2
5389
Source; consultant
As can be seen from the above tables, the forecasted AADT ‘s at mid-life of the design period is
shown below the table:
Table 5- 10: Design Standard for sections of the Project Road
Mid-Year
(2033) Design
Station
Project road segments
1
Road segment 6 and 7
1968
DC6
ERA 2013
Road segment 2 and 10
6839
DC7
ERA 2013
Road segment 3
6631
DC7
ERA 2013
Road segment 1-1
7891
DC7
ERA 2013
Road segment 1-2
9947
DC7
ERA 2013
Road segment 5
2598
DC6
ERA 2014
2519
DC 6
ERA 2013
2
3
Road segment 4,8 and
4
9
AADT
Standard
Remark
The design standard estimation for each station is as shown in the above, the road segments fall
on to DC6 and DC7 as per the projected traffic at midyear.
5.2.4
Terrain Classification
Topography and physical features play an important role in the location and design of a road. To
design a road economically and adequately and to entertain the different factors, the design
elements must be related to topographic features.
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In general, construction costs will be greater as the terrain becomes more difficult and higher
standards will become less justifiable or achievable in such situations than for roads in either flat or
rolling terrain. Drivers should also expect lower standards in such conditions and therefore adjust
their driving accordingly, so minimizing accident risk. Design speed will therefore vary with terrain.
Terrain class need to be established before a road is designed hence it needs to be defined
independently of the alignment that is finally selected for the road. It is determined by counting the
number of 5 meter contours crossed by straight line connecting the two ends of the road section in
question according to Ethiopian Roads Authority Geometric Design Manual, 2013 as shown below
Flat: 0-10 five meter contours per Km. the transverse ground slopes perpendicular to the
ground contours and generally below 3%
Rolling: 11-25 five-meter contours per km. the transverse ground slopes perpendicular to
the ground contours are generally between 3% and 25%
Mountainous: 26-50 five-meter contours per km. the transverse ground slopes
perpendicular to the ground contours are generally above 25%
Escarpment: are geological features that require special geometric standards because of
the engineering problems involved. They are characterized by more than 50
five meter contours per km and the transverse ground slopes perpendicular
to the ground contours are generally greater than 50%
Terrain classification is a useful tool which explains the physical characteristics of the project area
and its influence on drivers’ selection of operating speed. As such terrain type is directly related to
design speed for each functional class, and geometric design standard of roads as explained in
ERA Geometric Design Manual. Thus, the station wise terrain classification of the project is used to
set different design speeds and corresponding limiting values (minimum or maximum) for
geometric elements depending on the terrain type.
The project road has been studied thoroughly from 1:50,000 topographical maps, aerial photos
prior to and during a field reconnaissance. The detailed topographic survey results also examined
in order to classify the road corridor and accordingly the project road is classified in to sections of
varying terrain based on ERA terrain classification criteria, as it is presented in Table below.
Table 5- 11: Terrain Classification of the Road Project
NO
1
Station (KM)
Road
Segment From
0+000
AL-S1
0+420
1+500
To
0+420
1+500
6+026
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420.00
1080.00
4526.00
Type of Terrain
Rolling
Mountainous
Rolling
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Station (KM)
Road
Segment From
To
0+000
0+600
2
AL-S2
0+600
1+238
3
AL-S3
0+000
0+525
4
AL-S4
0+000
0+600
5
AL-S5
0+000
1+238
0+000
0+265
0+265
1+100
1+100
2+480
6
AL-S6
2+480
4+490
4+490
5+265
5+265
5+765
5+765
6+200
7
AL-S7
0+000
2+544
8
AL-S8
0+000
0+853
9
AL-S9
0+000
0+830
10
AL-S10
0+000
1+600
Table 5- 12: Percentage distribution of terrain
NO
Length (km)
600.00
638.00
525.00
600.00
1238.00
265.00
835.00
1380.00
2010.00
775.00
500.00
435.00
2544.00
853.00
830
1600
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Type of Terrain
Mountainous
Rolling
Rolling
Rolling
Rolling
Rolling
Mountainous
Rolling
Mountainous
Rolling
Mountainous
Rolling
Rolling
Rolling
Rolling
Rolling
Summary Of Terrain Classification
No.
Description of Terrain Type
Length (m)
Percentage
1
Escarpment
-
0
2
Mountainous
17061.25
80.265%
3
Rolling
4195.00
19.74%
4
Flat
0
As can observed in the table above, the project road mainly traverses through Rolling topography
which make up about 80.21% of the project length.
5.2.5
Type of area Classification
Sections of roads are also classified on the basis of the type of area (surrounding built and natural
environment) generally as “Rural”, “Rural Natural”,” Rural foot path”, “Peri-urban trading-centers”,
“Peri-urban” and “Urban”. The types and characteristics of roads differ in relation to the type of
area as the characteristics of road users differ depending on the type of area. The project area is
dominantly urban settlement, the project area is dominantly urban settlement; residential,
commercial, institutional, religious establishments and few government offices exist. The project
area seat as wereda seat.
5.2.6
ERA Design Standards
Based on ERA’s Geometric Design Manual DC6 standard is used for the Detail design of the road.
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Road users and their characteristics
Road users
 Vehicles,
 Non-motorized traffic
 Special road users such as unavoidable carts and animals that share the road facilities
To fulfil the fundamental objective of safety and efficiency of the road, the types, composition,
characteristics and interaction of all expected road users are studied.
The space, safety, access and mobility requirements of all types of road users are typically
considered in the design by
 classifying the project into different areas (Town, Village and rural areas), developing
different types of typical sections for each area and assigning appropriate design speed
 classifying the project road into different terrain classes and assigning different design
speeds
 designing the geometry considering the road users’ characteristics and expectations
(especially driver expectations) throughout the project road
Design Speed
The Design Speed is the selected speed which correlated with the terrain conditions and the
classification of the road class used to determine the various design of the road way.
Design elements such as lane width, horizontal radius, super elevation, sight distance and gradient
are directly related to design speed. Thus all of the geometric design parameters of a road are
directly related to the selected design speed.
In addition to this, various factors influence the speed of vehicles on a particular road. These
includes

Driver capability, driver culture and behaviour

Vehicle operating capabilities

The physical characteristics of the road and its surrounding

Weather

Presence of the other vehicles and

Speed limitation (Posted Speed limits)
When a change in topographical character or some other constraint necessitates a change in
alignment standard, the change should be made clear to the driver. This is best achieved by a
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sequence of horizontal curves, each having a predicted speed consistent with the design criterion.
When going from a high to a low standard, the predicted speed on sequential curves should not
differ by more than 10 km/h, and the speed environment relevant to each curve can be taken as
the predicted speed of the previous curve.
Design Vehicle
The selection of the appropriate design vehicle is a key element related to lane width, vertical
clearance, and minimum radius and turning paths at switch back curves and intersections. It also
affects design elements such as curve widening, maximum gradient, critical length of maximum
gradient, and provision of climbing lanes.
For the project road, the selected design vehicle is DV4 (Semi trailer combination) with the
following physical characteristics.
Table 5- 13: Design vehicle physical characteristics
Dimensions (m)
Design
Designation
Vehicle
Semi-Trailer
Combination
DV4
Overhang(m)
Height
Width
Length
Front
Rear
4.1
2.6
15.2
1.2
1.8
Wheel
Min.
base
Turning
(m)
Radius(m)
13.2
13.7
The minimum turning radius of DV4 vehicle is 13.7m, which is the absolute minimum internal
radius used in the design of hair-pin bends. The minimum offset of the rear wheel path is 0.5m as
shown in ERA Geometric standard.
It is stated in ERA ‘s geometric design manual 2013 that the present fleet in Ethiopia includes a
high number of four-wheel drive utility vehicles and overloaded trucks. Until more detailed
information becomes available regarding the makeup of the vehicle fleet in Ethiopia, the four
design vehicles indicated in the Table below should be used in the control of geometric design.
Table 5- 14: Design Vehicle
Design
Design
Vehicle
4x4
Utility
Vehicle
Single
Truck
Unit
Overhang
Overall (m)
Vehicle
(m)
Wheel
base (m)
Min. Design
Turning
Designation
Height
Width
Length Front
Rear
DV1
1.3
2.1
5.8
0.9
1.5
3.4
7.3
DV2
4.1
2.6
11.0
1.5
3.0
6.5
12.8
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Design
Vehicle
Single Unit Bus
Semi-Trailer
Combination
Design
Overhang
Overall (m)
Vehicle
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(m)
Designation
Height
Width
Length Front
Rear
DV3
4.1
2.6
12.1
2.1
2.4
DV4
4.1
2.6
15.2
1.2
1.8
Wheel
base (m)
7.6
Min. Design
Turning
Radius (m)
12.8
4.8+8.4=
13.2
13.7
Table 5- 15: Design Vehicle for each road class
Deign Standard
Design vehicle
DC8, DC7, DC6, DC5
DV4
DC4
DV4
DC3
DV3
DC2
DV3
DC1
DV1
Based on the ERA manual, appropriate design vehicle is placed for each road design standard as
shown in the Table 5.9 above. Since the project road has been categorized as DC6, the design
vehicle of DV4 has been used for design of the road. Moreover, for sections with sharp curve
(radius less than 40) in order to accommodate passage of single DV4 and a DV1 vehicle widening
of 1.5m is applied to both sides of the road.
The minimum turning radius of DV4 vehicle is 13.7m, which is the absolute minimum internal
radius used in the design of hair-pin bends. The minimum offset of the rear wheel path is 0.5m as
shown in ERA Geometric standard.
The design vehicle template is shown on Figure below.
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Figure 5- 1: Design Vehicle template
Pedestrians
The following special characteristics of pedestrians are taken into consideration during the design.
 Select the shortest path between two points.
 Have resistance to changes in gradient or elevation when crossing roadways and
 Avoid using inconvenient sections of roadway facilities such as muddy walkways
Pedestrian volume and activities are high to moderate in Towns than in villages and rural areas. In
rural areas of the project pedestrian volume and activities are found insignificant. Accordingly,
pedestrians as one of the major road users are considered in Town and village areas only.
Cyclists
Cyclist volume and activity is insignificant in the whole project area.
5.2.7
Selection of Design Standard Parameters and Their Limiting Values
On the basis of the design controls and criteria and the objective of the project discussed in the
above sections, a design standard consisting of limiting design values for the design of the different
features of the road is selected.
The design standard provided in the next sections is mostly derived from ERA Geometric design
standard with a few contextual modifications of some design element parameters to suit project
conditions and objectives.
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Geometric Design Elements
Table 5-11 below summarizes all the pertaining geometric design elements, parameters and
limiting design values (minimum or maximum) for design controls, horizontal alignment and vertical
alignment.
Table 5- 16: Design Standards
Design controls and elements of
Controls
Design
Item
design
Limiting values for design
Road Functional Classification
SAS and CS Road
Present Road Condition
10m to 15m wide shared road
RS (6 and 7), (2,10),3,1,5, (4,8,9)
Design Traffic volume
(1968,6839,6631,7891,9947,2598 and 2519) respectively
Geometric Design standard
DC6
Design Vehicle
DV4
Rural
Terrain and land use
Flat
Rolling
Mountainous Escarpment Village
Town
Design speed (km/hr)
100
85
70
60
50
50
g=0%
210
155
110
85
65
65
Stopping sight distance g=5%
240
175
120
90
70
70
(m)
g=10%
285
205
140
105
75
75
Minimum Passing sight distance (m)
375
330
270
230
180
180
515
350
215
145
95
95
curve SE=6%
455
310
195
135
85
85
SE=8%
410
280
175
120
-
-
Transition (spiral) curve requirement
No
No
No
No
No
No
Maximum super elevation
8
8
8
8
4
4
Design super elevation
As per Table 8.5 and 8.6 (ERA Manual 2013)
Design runoff length
As per Table 8.5 and 8.6 (ERA Manual 2013)
Percent passing opportunity (%)
SE=4% for urban
Minimum
Horizontal Alignment
Horizontal
radius
Minimum switch back curve inner
15
Alignment
Vertical
radius
15
Curve widening
As per Table 8.3 (ERA Manual 2013)
Maximum Gradient(Desirable)
3
5
7
7
6
6
Maximum Gradient(Absolute)
5
7
9
9
8
8
0.5
0.5
0.5
0.5
0.5
Minimum Gradient for curbed road and 0.5
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Design controls and elements of
Item
design
Limiting values for design
cut cross-section areas
Minimum gradient for uncurbed road at 0.5
0.5
0.5
0.5
0.5
0.5
No
No
No
No
No
No
100
55
30
17
10
25
18
12
9
7
Limiting K-factor for crest vertical 270
230
165
50
180
embankment areas
Climbing lane requirements
Limiting K-factor for crest vertical
curves(stopping sight distance)
Limiting
K-factor
for
sag
vertical
curves(stopping sight distance)
7
180
curves(passing sight distance)
Cross section Elements
10
Type of Surfacing
Asphalt
Carriageway width/cross fall
3m/2.5%
Shoulder surfacing/width/cross fall
-
-
-
3.5/6 (at
selected
Parking lane width/cross fall
-
place)
3.5/6
Curb requirement
yes
yes
yes
Walkway width/cross fall
2m/3%
yes
yes
Side slope
Refer sections below
Back slopes
Refer sections below
Road side ditches
Refer Typical sections
Cross sectional elements
Road width should be minimized so as to reduce the costs of construction and maintenance whilst
being sufficient to carry the traffic loading efficiently and safely.
Accordingly, various cross-sections are proposed, each addressing a specific need along that
portion of road traversed. Proposals are listed for
A. Side slopes for cuts and fills
Side slopes should be designed to insure the stability of the roadway and to provide a reasonable
opportunity for recovery of an out-of-control vehicle. Three regions of the roadside are important
when evaluating the safety aspects: the top of the slope (hinge point), the side slope, and the toe
of the slope (intersection of the fore slope with level ground or with a back slope, forming a ditch)
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The selection of side/back slopes has been made dependent upon stability (Soil extension), height
of fill or cut and type of material. The recommended cut and fill slopes extracted from ERA 2013
manual but slightly modified to suite site specific geological conditions and rock mass
characteristics
Table 5- 17: Slope Ratio Table – Vertical to Horizontal
Height
Material
of Side Slope (V:H)
Back Slope
Slope (m)
Fill
Earth
0.0 - 1.0
1:3
1:3
Soil/Decomposed
1.0 - 2.0
1:2
1:2
Rock
>2.0
2:3
2:3
0 .0 – 2.0
4:5
>2.0
1:1
4:1
0.0 – 2.0
2:3
2:1
>2.0
1:1
3:1
Strong Rock
Weathered Rock
Black Cotton Soil 0.0 – 2.0
1:6
(expansive Clays)(1)
1:4
>2
5.3
Geometrical Design of the Project Road
5.3.1
General
Cut
1:2
-
2:1
-
The Geometric design of the project road has been carried out with Civil 3D design Software. The
survey data in the form of X, Y, Z is loaded into the software to prepare a DTM model.
The road is designed in accordance with different design philosophies formulated depending on
the type of terrain and the type of area. Different design elements and parameters appropriate to
the design controls and criteria have also been prepared as described above which are specifically
employed depending on the context of the section of the road.
In the course of the design, maximum effort has also been exerted to achieve design consistency,
to meet road user expectations and perceptions of the designed road and its environment by
limiting speed changes within tolerable limits throughout the project road.
The design has been generally carried out to the selected minimum standard. In addition, where
design controls and constraints are not severe, the road is designed to a higher standard to
minimize future road upgrading costs.
5.3.2
Analysis Horizontal Alignment Design
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The project road is generally located in dominantly Rolling terrain and local Mountainous terrain.
But the horizontal alignment of the project road is designed for design speeds 50km/hr as town
section because our project is urban city project. The horizontal alignment is characterized by long
tangents and gentle curves in rolling sections and short tangent and sharp reverse in mountainous
sections.
The horizontal alignment of the detailed final design of the road is discussed in sections since it all
passes through rolling terrain.
For analysis purpose, the project road is divided into road segment sections as described below:
Table 5- 18: Road segment of the project road
RS-1
0+000-5+789.96
RS-2
0+000-1+238.25
RS-3
0+000-0+519.33
RS-4
0+000-0+591.32
RS-5
0+000-1+237
RS-6
0+000-6+186
RS-7
0+000-2+760
RS-8
0+000-0+861
RS-9
0+000-0+816.99
RS-10
0+000-1+655.99
The horizontal alignment geometry is separately analysed for all Road segment. The analysis
includes determination of the over length of curves and straight section, Table below.
Table 5- 19: Road segment by percentage curve lengths
S.No
Section
RS-1
Curve section (m)
Length
Straight section (m)
(m)
(M)
(%)
(M)
(%)
0 - 5789.96
5789.96
1958.181
33.82%
3831.779
66.18%
RS-2
0 -1238.25
1238.25
345.75
27.92%
892.5
72.08%
RS-3
0 - 519.33
519.33
137.803
26.53%
381.527
73.47%
RS-4
0 - 591.32
591.32
0
0.00%
591.32
100.00%
RS-5
0 - 1220
1220
179.689
14.73%
1040.311
85.27%
RS-6
0 - 6186.36
6186.36
2857.987
46.20%
3328.373
53.80%
RS-7
0 - 2767.04
2767.04
833.434
30.12%
1933.606
69.88%
RS-8
0 - 861
861
245.473
28.51%
615.527
71.49%
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RS-9
0 - 817
817
115.569
14.15%
701.431
85.85%
RS-10
0 - 1655.99
1655.99
0.000
0.00%
1655.99
100.00%
Generally, it can be observed from the summarized table that the overall percentage of length of
the curve is substantial in section 1. This is due to the difficult nature of the terrain along the route.
From the analysis in Table above, the road sections can be summarized into the following speed
ranges as provided in Table below the speed zones are:

<50 km /hr

Between 50 km /hr and 60 km/hr

Between 50 km /hr and 70 km/hr
Table 5- 20: Comparison of sections by speed distribution relative to the overall length of the curve
No
Road
segment
Road Section
<50km/hr
Length of Curved Stretch
Overall Length of
50km/hr-60km/hr 60km/hr-70km/hr
curve
RS-1
0 - 5789.96
1958.181
0
0
1958.181
RS-2
0 -1238.25
345.75
0
0
345.750
RS-3
0 - 519.33
137.803
0
0
137.803
RS-4
0 - 591.32
0
0
0
0.000
RS-5
0 - 1220
179.689
0
0
179.689
RS-6
0 - 6186.36
2857.987
0
0
2857.987
RS-7
0 - 2767.04
833.434
0
0
833.434
RS-8
0 - 861
245.473
0
0
245.473
RS-9
0 - 817
115.569
0
0
115.569
RS-10
0 - 1655.99
0
0
0
0.000
Total Length of Curves
6673.886
As it can be seen from the above table more than 100% of the curves are designed for design
speed 50km/hr.
Spatial distribution of horizontal curve radii
The reciprocal of the proposed radii and the minimum radii have been plotted against the
chainages along the section of the project road to appreciate the spatial distribution and extent of
the departures. The sections where the reciprocal of the proposed radii are greater than the
reciprocal of the minimum radii indicate the sections with departure from minimum radii and the
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larger the difference between the reciprocal of the proposed radii and the minimum radii, the higher
the extent of the departure.
Figure 5- 2: Reciprocal of radii plot against the Chainages for road segment 1: (0-5+789.96)
Figure 5- 3: Reciprocal of radii plot against the Chainages for Road segment 2: (0-1+238.25)
Figure 5- 4: Reciprocal of radii plot against the Chainages for Road segment 3: (0-0+519.33)
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Figure 5- 5: Reciprocal of radii plot against the Chainages for Road segment 5: (0-1+237)
Figure 5- 6: Reciprocal of radii plot against the Chainages for Road segment 6: (0-6+186)
Figure 5- 7: Reciprocal of radii plot against the Chainages for Road segment 7: (0-2+760)
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Figure 5- 8: Reciprocal of radii plot against the Chainages for Road segment 8: (0-0+861)
Figure 5- 9: Reciprocal of radii plot against the Chainages for Road segment 9: (0-0+817)
Built up areas (Towns section)
The horizontal alignment of the project road in built up areas is designed by bisecting the existing
right of way so that balanced right of obstructions could be removed. According to ERA manual the
typical town cross-sections are categorized for Region Seat, Zonal Seat, Wereda Seat and Kebele
seat. The project road traverses through Wereda Seat and Kebele seat. Chiro Town have master
plan accordingly; we provide the road way from the master plan. The towns and villages bisected
along the project road are provided in Table below.
Table 5- 21: Built up areas
Road
No.
Project Name
Estimated
Width (m)
Length (km)
1
Muz tera –TTC-Qilisa
5.78996
20
2
Kebt tera-Chiro Wereda Office
1.23825
20
3
Sumeya Bridge-Addis Ketema
0.51933
10
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Estimated
Project Name
Width (m)
Length (km)
4
Agape Hotel-Agri Reserch Center-TTC
0.59132
15
5
Agri Reserch Center-ODA Bultu University-Main Asphalt
1.237
15
6
Chiro Town Administration-Mtichu-Leila
6.189
20
7
Hundi Gudina Scl - Nejebac Kidane Mihret
2.76
15
8
Hundi Gudina Scl - Aschalew Hotel
0.861
10
9
Blood Bank-Gende Kuteba Bono
0.817
15
10
Chiro Wereda Office – Care Ethiopia
1.655.99
10
Total Length
5.3.3
21.66
Vertical Alignment
The ground profile along the proposed alignment is extracted from the ground model. Then, the
ground profile is traced with gradients and appropriate vertical curves using the vertical alignment
design options in Civil 3D Road design software. This has enabled us to have
 Gradient Information
 Vertical curve information of the existing and designed road
This information is compared with the limiting design values (minimum or maximum for design
standard, DC6) depending on the terrain type
The gradient is categorized into five classes to measure the severity of gradients as provided
below.
 0 to 4% - Gentle gradient with little impact on vehicle operation
 4 to 6% - Rolling gradient with moderate impact on vehicle operation
 6 to 10%- Hilly gradient with significant impact on vehicle operation
 10 to 12% - Grade beyond the limit DS5 standard which has significant impact on vehicle
operation and level of service of the road.
 >12% - Grade is difficult to impossible to be traversed by heavy trucks especially articulated
truck trailer combinations
The vertical alignment analysis is shown in the tables below.
Table 5- 22: Summary of Vertical Alignment Analysis Road segment -1
Grade
Number of
Distance along various Grades
Curves
0-400
400-1000
1000+
%
No
(m)
(m)
(m)
0-4
9
2147.46
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Percentage
(m)
%
2147.46
37.37%
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Distance along various Grades
Total
Percentage
(m)
%
1656.36
28.83%
1139.61
19.83%
406.12
802.81
13.97%
0
0
0.00%
5746.24
100.00%
Curves
0-400
400-1000
1000+
%
No
(m)
(m)
(m)
4.-6
6
1028.29
628.07
6-.9
5
1139.61
9-.12
2
396.69
>12
0
0
Total
Table 5- 23: Summary of Vertical Alignment Analysis Road segment -2
Number
Distance along various Grades
of Curves
0-400
400-1000
1000
%
No
(m)
(m)
(m)
0-4
1
4.-6
Grade
Total
Percentage
(m)
%
177.26
177.26
15.84%
2
468.46
468.46
41.86%
6-.9
1
319.83
319.83
28.58%
9-.12
1
153.53
153.53
13.72%
>12
0
0
0
0.00%
0
0
Total
1119.08
100.00%
Table 5- 24: Summary of Vertical Alignment Analysis Road segment -3
Grade
Distance along various Grades
Number of
Total
Percentage
(m)
%
247.49
247.49
68.59%
113.36
113.36
31.41%
0
0
0.00%
9-.12
0
0
0.00%
>12
0
0
0.00%
Curves
0-400
400-1000
1000+
%
No
(m)
(m)
(m)
0-4
2
4.-6
1
6-.9
Total
360.85
100.00%
Table 5- 25: Summary of Vertical Alignment Analysis Road segment -4
Grade
Number of
Distance along various Grades
Curves
0-400
400-1000
1000+
%
No
(m)
(m)
(m)
0-4
1
412.2
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Percentage
(m)
%
412.2
100.00%
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Distance along various Grades
Total
Percentage
(m)
%
0
0
0.00%
6-.9
0
0
0.00%
9-.12
0
0
0.00%
>12
0
0
0.00%
Curves
0-400
400-1000
1000+
%
No
(m)
(m)
(m)
4.-6
Total
412.2
100.00%
Table 5- 26: Summary of Vertical Alignment Analysis Road segment -5
Grade
Number of
Distance along various Grades
Total
Percentage
(m)
%
429.96
38.13%
697.63
61.87%
0
0
0.00%
9-.12
0
0
0.00%
>12
0
0
0.00%
1127.59
100.00%
Curves
0-400
400-1000
1000
%
No
(m)
(m)
(m)
0-4
2
429.6
4.-6
2
250.59
6-.9
447.04
Total
Table 5- 27: Summary of Vertical Alignment Analysis Road segment -6
Grade
Number of
Distance along various Grades
Total
Percentage
(m)
%
2880.77
2880.77
47.38%
6
1332.38
1332.38
21.91%
6-.9
8
1867.4
1867.4
30.71%
9-.12
0
0
0.00%
>12
0
0
0.00%
6080.55
100.00%
Curves
0-400
400-1000
1000
%
No
(m)
(m)
(m)
0-4
13
4.-6
Total
Table 5- 28: Summary of Vertical Alignment Analysis Road segment -7
Grade
Number of
Distance along various Grades
Curves
0-400
400-1000
1000+
%
No
(m)
(m)
(m)
0-4
4
1148.3
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Percentage
(m)
%
1148.3
45.08%
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Distance along various Grades
Curves
0-400
400-1000
1000+
%
No
(m)
(m)
(m)
4.-6
2
6-.9
2
891.35
507.74
9-.12
>12
0
Total
Total
Percentage
(m)
%
891.35
34.99%
507.74
19.93%
0
0.00%
0
0.00%
2547.39
100.00%
Table 5- 29: Summary of Vertical Alignment Analysis Road segment -8
Grade
Number of
Distance along various Grades
Total
Percentage
(m)
%
595.43
595.43
81.91%
131.47
131.47
18.09%
6-.9
0
0.00%
9-.12
0
0.00%
0
0.00%
Curves
0-400
400-1000
1000+
%
No
(m)
(m)
(m)
0-4
3
4.-6
1
>12
0
Total
726.9
100.00%
Table 5- 30: Summary of Vertical Alignment Analysis Road segment -9
Grade
Number of
Distance along various Grades
Curves
0-400
400-1000
1000
%
No
(m)
(m)
(m)
0-4
3
701.59
400.7
Total
Percentage
(m)
%
1102.29
88.63%
0
0.00%
141.36
11.37%
0
0.00%
0
0.00%
4.-6
6-.9
1
141.36
9-.12
>12
0
Total
1243.65
100.00%
Table 5- 31: Summary of Vertical Alignment Analysis Road segment -10
Grade
Number of
Distance along various Grades
Curves
0-400
400-1000
1000
%
No
(m)
(m)
(m)
0-4
3
416.42
655.74
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Percentage
(m)
%
416.42
51.49%
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Total
Percentage
(m)
%
392.31
48.51%
6-.9
0
0.00%
9-.12
0
0.00%
0
0.00%
Curves
0-400
400-1000
1000
%
No
(m)
(m)
(m)
4.-6
2
392.31
>12
0
Total
808.73
100.00%
Spatial distribution of gradients
The proposed grades, the maximum grade (8%) and the minimum grade (0.5%) have been plotted
against the Chainages along the section of the project road to appreciate the spatial distribution
and extent of the departures. The sections where the proposed grades are greater than the
maximum grade indicate departure from maximum grade and the larger the difference between the
proposed grade and the maximum grade, the higher the extent of the departure.
Figure 5- 10: Spatial distribution of gradients for road segment 1: (0+000 – 5+789.96)
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Figure 5- 11: Spatial distribution of gradients for road segment 2: (0+000 – 1+238.25)
Figure 5- 12: Spatial distribution of gradients for road segment 3: (0+000 – 0+519.33)
Figure 5- 13: Spatial distribution of gradients for road segment 4: (0+000 – 0+591.32)
Figure 5- 14: Spatial distribution of gradients for road segment 5: (0+000 – 1+237)
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Figure 5- 15: Spatial distribution of gradients for road segment 6: (0+000 – 6+186)
Figure 5- 16: Spatial distribution of gradients for road segment 7: (0+000 – 2+760)
Figure 5- 17: Spatial distribution of gradients for road segment 8: (0+000 – 0+861)
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Figure 5- 18: Spatial distribution of gradients for road segment 9: (0+000 – 0+817)
Figure 5- 19: Spatial distribution of gradients for road segment 10: (0+000 – 1+655.99)
5.3.4
Draft Engineering Design Drawings
The plan profile drawings will be submitted with the draft tender documents as a separate volume.
5.4
Requested Departures from Standard
5.4.1
General
Despite the range of flexibility with standards that exists with respect to virtually all the significant
road design features, there are situations in which the application of even the minimum criteria
(including any allowable Relaxations) would result in safety, technical, programme, financial or
environmental negative impacts greater than the benefits that would be obtained by incorporating
the proposed Departure.
Highway design usually encompasses multi-disciplinary dimensions that need thorough
assessment, analysis and optimizations. Considering these, each project is better studied and
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designed in a context sensitive manner. Context Sensitive Design is a collaborative,
interdisciplinary approach that involves all constituents to develop a transportation facility that fits
its physical setting and preserves scenic, aesthetic, historic and environmental resources,
while maintaining safety and mobility to all road users, and enhancing the economic, social
and other needs of the society.
In terms of this concept, it is assumed that every project is unique which requires designers to
address the needed roadway improvements while safely integrating the design into the unique
surrounding natural and built environment.
The hallmark of professionalism in highway design is the ability to foresee and optimize the
conflicting objectives that are inherent in any project. Many of the design controls and criteria of
highway design are often conflicting in nature. Good highway design is the art of combining and
balancing the various controls in a perceptive fashion and is not merely an exercise in three
dimensional geometrics. These different objectives of road engineering should be prioritized
initially according to their importance to the specific project. For instance, a section of high
standard road that has to pass through a deep reserved forest may have to be designed to the
lowest design standard possible to minimize negative impacts to the forest.
Geometric design standards often try to define acceptable level of service, and margin of safety
with limited emphasis on roadway aesthetics. However, they barely define acceptable level of
stability, acceptable level of social and environmental impacts. So, often locally compromising
geometric design standards to fulfil these other important objectives of highway design in an
optimal manner becomes imperative especially in difficult topography.
It is also good to note that standards usually give guidance whenever the terrain and other
associated factors are in favour of the selected geometric design standard. Nowadays the name
“manual” is being replaced with “Guide to”. This manifest that “manuals” are sensed as more
restricting to the designer to use his judgment and experience. The purpose of this replacement is
thus to give the designer more space and flexibility to arrive at balanced design in reconciliation the
different contrasting objectives of road facilities at selected localized sections. Therefore, the
geometric design standards summarized in ERA manual should be intended to provide guidance
for designers rather than to be considered as rigid minima.
Departures from standard made to produce optimized design with varying level of compromise
among the contrasting multi-objectives of highway facilities including safety, stability, serviceability,
economy, environmental and social compatibility, and practicality of the design for construction and
maintenance are therefore often required especially in roadways that traverse through difficult
terrain conditions and sensitive social and environmental areas. Due to the varying nature of
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Departures, their interaction with each other and the existing and future route conditions, each
Departure is unique.
5.4.2
List of Requested Departures from Standard
The Requested departures from the standard in the section include departure from minimum radii,
departure from maximum grade, and gradients at switch back curves as presented in the following
tables.
Table 5- 32: Departure from Minimum Horizontal Curve Radii for Road segment-1
Curve Station
No.
Curve
From
To
Length(m)
Radius(m)
Deflection Minimum
angle(0)
Radius(m)
Departure
1
0+418.84
0+444.73
25.89
40
37.0843
95
Departed
2
0+505.05
0+549.29
44.244
500
5.07
95
OK
3
0+675.32
0+723.86
48.537
95
29.2735
95
OK
4
0+755.52
0+844.15
88.624
95
53.4506
95
OK
5
0+979.23
1+022.49
43.265
340
7.2909
95
OK
6
1+179.31
1+259.92
80.617
300
15.3968
95
OK
7
1+384.59
1+493.75
109.155
95
65.8331
95
OK
8
1+603.17
1+646.14
42.967
300
8.206
95
OK
9
1+755.92
1+863.61
107.696
150
41.1367
95
OK
10
2+089.41
2+277.41
188.001
95
113.386
95
OK
11
2+332.91
2+403.54
70.624
30
134.8825
95
Departed
12
2+447.24
2+525.46
78.212
55
81.4768
95
Departed
13
2+556.26
2+711.55
155.291
95
93.658
95
OK
14
2+828.20
2+883.69
55.495
135
23.5526
95
OK
15
2+978.84
3+096.42
117.572
95
70.9095
95
OK
16
3+207.74
3+278.14
70.398
600
6.7225
95
OK
17
3+347.81
3+409.93
62.127
165
21.5735
95
OK
18
3+571.44
3+631.36
59.915
300
11.443
95
OK
19
3+841.13
3+889.15
48.023
420
6.5512
95
OK
20
4+027.66
4+107.67
80.013
200
22.922
95
OK
21
4+354.96
4+398.61
43.655
400
6.2531
95
OK
22
4+480.37
4+522.37
42.002
400
6.0163
95
OK
23
4+636.02
4+698.33
62.314
400
8.9258
95
OK
24
4+972.67
5+109.48
136.814
150
52.2592
95
OK
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5+318.48
5+415.21
96.73
80
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69.2777
95
Departed
Table 5- 33: Departure from Minimum Horizontal Curve Radii for Road segment-6
Curve
Station
No.
From
Curve
To
Length(m)
Radius(m)
Deflection
Minimum
angle(0)
Radius(m)
Departure
1
0+084.80 0+131.70
46.895
200
13.43
95
OK
2
0+179.07 0+221.48
42.4
300
8.10
95
OK
3
0+253.12 0+271.30
18.181
230
4.53
95
OK
4
0+307.57 0+362.74
55.17
230
13.74
95
OK
5
0+424.72 0+567.01
142.282
160
50.95
95
OK
6
0+657.87 0+707.11
49.232
95
29.69
95
OK
7
0+750.11 0+793.94
43.835
95
26.44
95
OK
8
0+845.58 0+907.89
62.304
95
37.58
95
OK
9
1+035.15 1+084.33
49.183
120
23.48
95
OK
10
1+146.13 1+192.72
46.586
95
28.10
95
OK
11
1+232.18 1+257.48
25.299
200
7.25
95
OK
12
1+325.01 1+368.66
43.652
200
12.51
95
OK
13
1+439.94 1+496.56
56.62
55
58.98
95
Departed
14
1+526.93 1+603.72
76.792
65
67.69
95
Departed
15
1+707.92 1+758.95
51.035
150
19.49
95
OK
16
1+815.42 1+887.68
72.262
65
63.70
95
Departed
17
1+946.17 1+999.74
53.576
95
32.31
95
OK
18
2+093.89 2+317.00
223.105
95
134.56
95
OK
19
2+422.62 2+463.26
40.636
250
9.31
95
OK
20
2+582.42 2+655.74
73.316
175
24.00
95
OK
21
3+023.03 3+109.57
86.545
300
16.53
95
OK
22
3+248.26 3+379.02
130.758
175
42.81
95
OK
23
3+601.49 3+673.39
71.896
100
41.19
95
OK
24
3+754.75 3+914.52
159.771
70
130.77
95
Departed
25
3+951.03 4+121.84
170.81
170
57.57
95
OK
26
4+238.50 4+296.04
57.534
175
18.84
95
OK
27
4+455.64 4+574.83
119.196
175
39.03
95
OK
28
4+678.67 4+718.47
39.797
400
5.70
95
OK
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Curve
No.
Station
Curve
From
Length(m)
To
Radius(m)
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Minimum
angle( )
Radius(m)
0
Departure
29
4+880.69 5+026.81
146.113
112
74.75
95
OK
30
5+242.72 5+282.30
39.573
280
8.10
95
OK
31
5+379.78 5+731.65
351.867
141
142.98
95
OK
32
5+781.19 5+861.46
80.272
375
12.26
95
OK
33
5+923.03 6+054.52
131.494
150
50.23
95
OK
Road segment-2,3,4,5,7,8,9 and 10 has no departure from minimum radii.
Table 5- 34: Departure from Maximum Grade for Road segment -1
Station
No
Grade
Grade
Desirable
Absolute
Length
Maximum
Maximum
(m)
Grade (%)
Grade (%)
From
To
(%)
1
0+000.00
0+176.17
-4.50%
176.17
6.00%
8.00%
2
0+176.17
0+329.06
-8.00%
152.89
6.00%
8.00%
3
0+329.06
0+443.24
1.00%
114.18
6.00%
8.00%
4
0+443.24
0+839.93
12.00%
396.69
6.00%
8.00%
5
0+839.93
1+008.16
6.00%
168.23
6.00%
8.00%
6
1+008.16
1+144.31
7.74%
136.15
6.00%
8.00%
7
1+144.31
1+395.17
4.00%
250.86
6.00%
8.00%
8
1+395.17
1+675.29
7.76%
280.12
6.00%
8.00%
9
1+675.29
1+989.40
-2.44%
314.11
6.00%
8.00%
10
1+989.40
2+179.85
5.15%
190.45
6.00%
8.00%
11
2+179.85
2+401.97
-1.18%
222.12
6.00%
8.00%
12
2+401.97
2+591.89
-3.21%
189.92
6.00%
8.00%
13
2+591.89
2+907.60
3.78%
315.71
6.00%
8.00%
14
2+907.60
3+230.40
-3.62%
322.8
6.00%
8.00%
15
3+230.40
3+544.37
5.70%
313.97
6.00%
8.00%
16
3+544.37
3+830.87
3.02%
286.5
6.00%
8.00%
17
3+830.87
4+010.34
6.00%
179.47
6.00%
8.00%
18
4+010.34
4+371.06
7.83%
360.72
6.00%
8.00%
19
4+371.06
4+999.13
6.00%
628.07
6.00%
8.00%
20
4+999.13
5+208.86
-6.63%
209.73
6.00%
8.00%
21
5+208.86
5+340.12
1.00%
131.26
6.00%
8.00%
22
5+340.12
5+746.24
11.95%
406.12
6.00%
8.00%
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Table 5- 35: Departure from Maximum Grade for Road segment -2
Station
No
Grade
Grade
Desirable
Absolute
Length
Maximum
Maximum
(m)
Grade (%)
Grade (%)
Departure /
From
To
(%)
Relief
1
0+000.00
0+150.03
-6.00%
150.03
6.00%
8.00%
2
0+150.03
0+469.86
-8.00%
319.83
6.00%
8.00%
3
0+469.86
0+826.64
-5.86%
356.78
6.00%
8.00%
4
0+826.64
0+965.54
-11.09%
138.9
6.00%
8.00%
Departed
5
0+965.54
1+119.08
1.01%
153.54
6.00%
8.00%
Global Relief
Global Relief
Table 5- 36: Departure from Maximum Grade for Road segment -2
Station
No
Grade
Grade
Desirable
Absolute
Length
Maximum
Maximum
(m)
Grade (%)
Grade (%)
Departure /
From
To
(%)
1
0+000.00
0+194.19
1.40%
194.19
6.00%
8.00%
Global Relief
2
0+194.19
0+443.80
8.92%
249.61
6.00%
8.00%
Departed
3
0+443.80
0+658.92
3.72%
215.12
6.00%
8.00%
Global Relief
4
0+658.92
0+938.70
8.77%
279.78
6.00%
8.00%
Departed
5
0+938.70
1+182.13
5.40%
243.43
6.00%
8.00%
6
1+182.13
1+418.33
-6.87%
236.2
6.00%
8.00%
7
1+418.33
1+538.53
0.62%
120.2
6.00%
8.00%
8
1+538.53
1+688.57
5.63%
150.04
6.00%
8.00%
9
1+688.57
1+855.55
-0.74%
166.98
6.00%
8.00%
10
1+855.55
2+073.34
4.28%
217.79
6.00%
8.00%
11
2+073.34
2+286.81
5.55%
213.47
6.00%
8.00%
12
2+286.81
2+469.97
-1.75%
183.16
6.00%
8.00%
13
2+469.97
2+632.83
-7.38%
162.86
6.00%
8.00%
14
2+632.83
2+797.02
1.09%
164.19
6.00%
8.00%
15
2+797.02
2+934.12
-2.99%
137.1
6.00%
8.00%
16
2+934.12
3+176.63
7.03%
242.51
6.00%
8.00%
17
3+176.63
3+397.01
1.21%
220.38
6.00%
8.00%
18
3+397.01
3+727.67
-8.00%
330.66
6.00%
8.00%
19
3+727.67
3+929.77
-5.50%
202.1
6.00%
8.00%
20
3+929.77
4+303.11
-2.26%
373.34
6.00%
8.00%
21
4+303.11
4+550.93
-8.00%
247.82
6.00%
8.00%
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Station
No
Grade
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Grade
Desirable
Absolute
Length
Maximum
Maximum
(m)
Grade (%)
Grade (%)
From
To
(%)
22
4+550.93
4+917.51
-3.84%
366.58
6.00%
8.00%
23
4+917.51
5+135.66
-0.53%
218.15
6.00%
8.00%
24
5+135.66
5+441.21
-6.00%
305.55
6.00%
8.00%
25
5+441.21
5+749.41
-2.59%
308.2
6.00%
8.00%
26
5+749.41
5+962.59
1.61%
213.18
6.00%
8.00%
27
5+962.59
6+080.55
-7.17%
117.96
6.00%
8.00%
5.4.3
Departure /
Relief
Reasons and Justifications for the Requested Departures from Standard
In the rugged mountainous and escarpment sections of the project route, achieving the required
geometric design parameters for DC6 paved Design standard, like limiting the maximum gradient
to 8%, the minimum radius of curve to 95m for urban and per urban has been difficult due to
considerably high earthwork quantities, construction costs above the feasible range, significant
negative environmental impacts and increased risk of cut slope instabilities and overall
performance of the project road.
The reasons and explanation for the requested departures from the standard have been
assembled separately for the horizontal alignment and vertical alignment. The sample reasons for
the requested departures from standard have also been presented in tabular forms and illustrated
with extracted Plan, profiles and cross sections.
Reasons for minimum radius of curves
The core reason for the requested departures from minimum horizontal radius is the rugged
mountainous terrains that form about 19.74% of the road section which has very sharp natural
curvatures. At sharp natural curvature locations in such difficult terrains only departed sharp radii of
curvatures can fit without excessive height of fill, excessive height of retaining walls, and excessive
depth of cuts and associated stability problems. Furthermore, in traversing steep ascent and
descent sections, the use of winding alignment with the inclusion of sharp switch back curves (hairpin bends) becomes important.
The estimated depth of deep box cuts, that would be required at each curve locations if improved
to minimum values are presented as one of the reasons for the requested departure from standard
as shown in the figure below.
Section 8.9 of ERA Geometric Design Manual 2013 states
“Switchback or hairpin curves are used where necessary in traversing mountainous and
escarpment terrain. Employing a radius of 20m or less, with a minimum of 10m, they are generally
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outside of the standards for all road designs, and are specified using the guidelines listed in the
Departure from Standards section in chapter 2.”
Reasons for departure from maximum gradient
Similar to the case for minimum radius of Horizontal Alignment, the main reasons for the requested
departure from maximum gradient is the rugged mountainous and escarpment topography that
form nearly 73% of the section of the project road associated with steep rise and fall sections.
The major reason for departure is huge depth cuts which range from 10m to 30m and more if we
make the grade continuous. These depths of cuts are excessively high with considerably high
construction costs, maintenance costs, instability costs, and social and environmental costs. So,
using 9% maximum grade as provided in the geometric design manual is concluded to be
impractical at selected sections.
The tabulated reasons for departure are illustrated with profile and cross section drawings below.
Figure 5- 20: Illustration of the effects of using 8% maximum grade resulting in 11.2m deep cut at
sta. 0+660 ( Road segment -1)
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Figure 5- 21: Illustration of the effects of using 9% maximum grade resulting in high fill 7.4 from sta.
2+300 to sta. 2+642 for ( Road segment -6)
In design of roads through mountainous and escarpment terrains, hill side cut cross sections that
flash with the ground at the valley side are mostly expected which are often in harmony with the
surrounding natural topography. This can only be achieved through the use of horizontal
curvatures in balance with the natural curvatures and gradients in balance with the natural
topography as can be appreciated in the photo below.
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High fill
supported
Deep
by
box cut
cross
Figure 5- 22: Exhibit 5.1: Fig 4.08
Mountain road in Jordan showing appropriate design in difficult conditions (Rendel Palmer & Tritton)
(Source: TRL released Note titled towards Safer Roads)
Despite the above harmonious design approach, we may use minimum radii of horizontal curves
from standards that may be way larger than the natural ground curvatures and gentle gradients
that slush through the topography. Such a design approach would result in deep box cut cross
sections on the convex side of the hill and high fill embankments supported by huge retaining walls
on the concave side of the hill.
When the road offsets more to the valley side at the concave section of the hill due to use of larger
radius curves, the height of retaining wall and fill embankment becomes excessively large.
Similarly, when the road offsets more to the hill side at the convex section of the hill due to use of
larger radius curves, the depth of the box cut cross sections becomes excessively large.
It is also well known that deep box cut cross sections are not generally favourite cross section
types in low volume road design as they have a number of disadvantages:
 They are not environmentally friendly as they slash through the natural topography and
leave heavy construction scars resulting in steep and long roadside slopes susceptible to
erosion and incapable of supporting of vegetation/plant cover and topsoil (or disfigured
landscape)
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 Unavoidable side-tipping of excessive spoil materials from road cuts will cause additional
significant damages to the landscape, and contribute to the decrease in stability of slopes.
 The resulting excessive spoil material can give rise to a variety of problems including
erosion of the spoil itself, the smoothening or removal of natural vegetation, instability within
the spoil material itself, especially when infiltrated by water, slope overloading and resultant
failure and disruption of existing runoff patterns and siltation of water courses and drainage
channels and disruption of agricultural practices
 In addition to intrusion in landscape, deep excavation of the slope invariably disturbs the
natural stability of the ground by the removal of lateral support and a change in the natural
ground water conditions which may trigger slope instability problems
 They also take up extensive land area as the slope stake distances are very large on both
sides. Such a huge land takes in such a project area where land for farming is limited due
to severe topography may also have negative effect on the welfare of the local society.
So keeping the radius of curvature and gradients in balance with the natural topography through
the employment of departures from standards in difficult terrains would often result in a wellblended, environmentally more sustainable, economical and more stable road.
5.4.4
Mitigation Measures
Even though Road design should be as forgiving as possible as a matter of good practice,
Mitigation measures for design exceptions are normally investigated and considered. When
mitigation is proposed as part of the design exception request, it is notified in terms of the required
measures to be provided in the project.
Minimum Horizontal Radius
The following are the proposed mitigation measures that are believed to minimize the negative
safety and serviceability concerns of sharp curves:

Providing adequate traffic signs, pavement markings, and guide posts

Providing guard rails at selected locations especially where sharp curves and steep grades
co-exist
Switch back curves
Speed restriction is the main criterion to be maintained through-out switch back curves. A vehicle
can negotiate 20m curve without encroaching into other traffic lanes at a design speed of about
20km/hr and lesser.
The following are specific mitigation measures:
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
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Providing adequate traffic signs including warning and chevron traffic signs, and pavement
markings,

Providing guideposts with reflectors

Providing guard rails at selected locations especially where switch back curves and steep
grades co-exist
Maximum Gradient
When a gradient is more than the desirable maximum gradient, its length is limited to the maximum
desirable length. Further a relief gradient of maximum 6% is provided with a minimum length of
150m. This will give heavy vehicles time to change gears and acquire momentum to negotiate the
next steep gradient. This also enhances the safety of the road by decreasing the unnecessary high
speeds of descending vehicles.
In addition to the above geometric mitigation measures, appropriate traffic signs and pavement
markings will be provided that will warn and guide drivers through the steep grade sections safely
and comfortably.
5.4.5
Conclusion and Recommendations
The following are concluded from the discussions in this Reasons and Justifications for departures
from standards report.
 The main reason for the requested departures from minimum horizontal radius is to reduce
the way it passes through cemeteries
 The majority of the ground profile vertical alignment of the project site traverses through
mountainous and escarpment terrain either continuously rising (ascending) or falling
(descending) which make it difficult to achieve the required standard.
 Anticipated geotechnical instability and increased risk of cut slope failures due to very deep
cut and high fill.
 Inaccessibility of the road to people and animals living by the sides of the road due to the
deep cut
Considering the foregoing, we strongly believe that the requested departures from standards and
their extents are reasonable and kindly request the approval of the proposed design along with the
requested departures from the standards.
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6
ROAD SAFETY DESIGN
6.1
Review of Existing Accident Data
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The burden of road traffic injuries and fatalities is huge in Ethiopia. WHO’s Global status report on
road safety 2013 revealed that approximately 1.24 million people die every year on the world’s
roads; another 20 to 50 million sustain nonfatal injuries as a result of road traffic crashes which is
the leading cause of death for young people aged between 15-29 years. A similar WHO’s status
report on road safety for African region 2009 affirmed that almost 20% (n = 234 768) of global road
traffic deaths occurred in the African Region which has less than 2% of the world’s registered
vehicles and of all the deaths in the Region 70% occurred in the ten countries that account for 70%
of the regional population: Ethiopia, Ghana, Kenya, Madagascar, Mozambique, Nigeria, South
Africa, Tanzania, Uganda. The region has some of the highest rates of road traffic deaths globally
at more than 32 deaths per 100,000 populations annually. According to the report, Ethiopia has 35
deaths per 100,000 populations which is among the few highest rates in the world.
The traffic police reported road traffic crash data from 2003 to 2008 has been analysed and
presented in a study by UN (Road safety in Africa, a case study in Ethiopia). A more recent review
of police reported traffic crash data has been made by Getu. Sagne et.al. We referred to these
documents to establish the current road safety statistics for the country.
Table 6- 1: Motor vehicle accidents in Ethiopia, 2003/04 - 2007/08
2003/04
2004/05 2005/06 2006/07
2007/08
Total accidents
15,346
17,722
18,911
17,147
15,086
Fatal
1,630
1,801
2,029
2,047
1,802
Serious Injury
2,072
2,368
2,621
2,504
2,156
Light Injury
2,705
2,731
2,653
2,426
2,123
Property damage
10,569
10,822
11,608
10,170
9,005
Death rate per ten thousand vehicles
145
132
137
123
95
Death rate per hundred thousand population
3.10
3.13
3.51
3.41
2.84
Number of deaths
2,111
2,188
2,522
2,517
2,161
Below 18 years age
435
494
513
506
485
18-30 years age
858
791
1,139
977
689
31-50 years age
570
678
592
721
642
Above 50 years
248
225
278
313
345
Number of people injured
8,507
8,885
9,394
9,553
7,140
Below 18 years age
1,552
1,490
1,900
1,884
1,091
18-30 years age
3,703
4,429
4,352
3,847
3,025
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Data Source: Federal Police Commission
Of the total traffic accidents occurring yearly, more that 11% are fatal accidents. Over 20 % of the
total traffic accident injuries are fatalities.
Table 6- 2: Severity of traffic accidents in Ethiopia
Ethiopian
Fiscal Year
Ethiopian
Severity of Accidents
Fatal
Severity of Injuries
Total
%
Fatal Total
Total
Fatalities as %
Fiscal Year Accidents
Accidents
Accidents
Fatalities
Injuries
of injuries
2003/4
1,630
15,346
10.6
2,111
10,618
19.9
2004/5
1,801
17,722
10.2
2,188
11,073
19.8
2005/6
2,029
18,911
10.7
2,522
11,916
21.2
2006/7
2,047
17,147
11.9
2,517
12,070
20.9
2007/8
1,802
15,086
11.9
2,161
9,301
23.2
Data Source: Federal Police Commission
The majority of crashes occurred during daylight hours. Figure 6-1 shows that crashes increased
rapidly from 6:00am to 7:00am. Numbers were more or less steady until 8:00 pm after which they
declined in most cases, though not as steeply as the morning increase. Figure 5- 3 provides traffic
volume data by hour for several important roads.
Figure 6- 1: Variation in Road Traffic Crashes By Figure
Time of Day, July 2005-June 2011
6- 2:
Motorized
Traffic
Volume
Time of Day on Selected Major Road Segments in
2011 (Ethiopian Roads Authority, 2012).
The highest number of crashes (fatal, injury, and property damage) involved drivers in the 18 – 30year age group (45%) and in the 31-50-year age group (35%). The age range of drivers involved in
crashes is shown in Table below.
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Table 6- 3: Crashes by Driver Age, Education, and Gender, July 2005-June 2011
Driver Age
Fatal
Injury
Property
Total
%
Less than 18
342
775
766
1,883
1.8
18-30
6,005
14,182
25,624
45,811
44.5
31—50
3,853
9,027
23,491
36,371
35.3
More than 51
764
2,023
6,276
9,063
8.8
Unclassified age
1,176
3,447
5,279
9,902
9.6
Total
12,140
29,454
61,436
10,3030
100.0
Illiterate
374
607
526
1,507
1.46
Writing & reading
598
1,192
1,641
3,431
3.33
Elementary school
2,644
5,327
8,762
16,733
16.24
Junior high school
3,484
8,374
12,838
24696
23.97
High school
3,235
8,638
23,612
35,485
34.44
Above high school
1,077
2,588
9,844
13,509
13.11
Unknown
728
2,728
4,213
7,669
7.44
Total
12,140
29,454
61,436
103,030
100.00
Male
10,928
25,628
54,005
90,561
87.90
Female
684
1,462
3,534
5,680
5.51
Unclassified
528
2,364
3,897
6,789
6.59
Total
12,140
29,454
61,436
103,030
100.00
Driver Education Level
Driver Gender
Interstate and city roads accounted for 70.5% of fatal crashes for most of which ERA is responsible.
Most of these are paved two-way two-lane roads.
Table 6- 4: Road Traffic Fatality Crashes by Road Type and Road Pavement July 2005-June 2011
Road Type
Twelve Month Periods (July-June)
2005/6
2006/7
2007/8
2008/9
2009/10
2010/11
Total
%
Interstate
728
758
768
606
473
1027
4360
35.9
Collector
211
237
238
300
375
509
1870
15.4
Access
237
327
351
224
360
215
1714
14.1
City
625
707
690
672
1003
499
4196
34.6
Total
1801
2029
2047
1802
2211
2250
12140
100
1534
1494
8144
67.1
Road Traffic Fatality Crashes by Road Pavement ( Surface) Type
Asphalt roads
1237
1429
1208
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Twelve Month Periods (July-June)
2005/6
2006/7
2007/8
2008/9
2009/10
2010/11
Total
%
76
65
66
75
221
354
857
7.1
Gravel roads
379
416
471
314
356
397
2333
19.2
Earth roads
109
119
302
171
100
5
806
6.6
Total
1801
2029
2047
1802
2211
2250
12140
100
Asphalt roads with
some distress
The absence of median strips or barriers also has a significant effect in increasing crashes. Usually,
rural two-lane roads lack these physical barriers which separate opposing the incoming and
outgoing traffic flows. Two-way, two-lane roads constitute the major proportion in of the road
network in Ethiopia.
Table 6- 5: Fatal and Injury Crashes in the Six Year Period by Lanes/Medians, Road Alignment,
Junction Type and Illumination Conditions
Fatal
Crashes
%
Injury
crashes
%
Lanes/Medians
One way
3020
24.88
6391
21.7
Undivided Two way
7278
59.95
16631
56.46
Double carriageway ( median)
1482
12.21
5335
18.11
Two-way ( divided with solid lines road marking)
236
1.94
727
2.47
Two-way ( divided with broken lines road marking )
124
1.02
259
0.88
Total
12140
100.00
29454
100
Tangent road with flat terrain
7,913
65.18
19832
67.33
Tangent road with mild grade and flat terrain
1,166
9.60
2797
9.50
and 348
2.87
816
2.77
Tangent road with rolling terrain
337
2.78
909
3.09
Gentle horizontal curve
587
4.84
1,325
4.50
Sharp reverse curve
525
4.32
1,069
3.63
Steep grade upward with mountainous terrain
515
4.24
990
3.36
Steep grade downward with mountainous terrain
669
5.51
1,478
5.02
Other
80
0.66
238
0.81
Total
12,140
100.00
29,454
100.00
Road Alignment
Tangent
road
with
mountainous
terrain
escarpments
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Injury
%
crashes
%
Lanes/Medians
Illumination conditions
Daytime with sufficient daylight
7,581
62.5
20,094
68.22
Twilight
871
7.17
2,004
6.80
Sun rising
874
7.20
1,590
5.40
Night with sufficient light
1,293
10.7
2,470
8.39
Night with insufficient light
542
4.46
1,519
5.16
Night without light
781
6.43
1,407
4.78
Other
198
1.63
370
1.26
Total
12,140
100.00
29,454
100.00
Midblock
8,565
70.55
21,977
74.61
Y-junction
1,570
12.93
2,030
6.89
T-junction
742
6.11
2,367
8.04
Roundabout
371
3.06
848
2.88
Four leg junction
539
4.44
1,600
5.43
Five leg junction
95
0.78
111
0.38
Rail crossing
34
0.28
68
0.23
Other
224
1.85
453
1.54
Total
12,140
100.00
29,454
100.00
Road junction type
There are also links between different land use types and the occurrence of crashes. Analysis
indicates that most fatal and injury crashes occurred in and around cities, particularly in central
business districts and residential areas. Table below shows that 27.7% fatalities and 33.4% of
serious injuries occurred in central business districts and residential areas in the six-year period.
Table 6- 6: Crashes by Land Use
Land use
Fatal Crashes
%
Injury Crashes
%
Property Damage
%
Rural village areas
3041
25.0
4737
16.0
4334
7.1
Agriculture areas
1948
16.1
3584
12.1
4360
7.1
School areas
892
7.4
1903
6.5
2379
3.9
Industrial
355
2.9
929
3.2
1554
2.5
Church areas
462
3.8
1369
4.7
2855
4.7
Market areas
820
6.8
3147
10.8
6748
10.9
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Land use
Fatal Crashes
%
Injury Crashes
%
Property Damage
%
Recreational areas
562
4.6
1908
6.4
4505
7.3
Hospital areas
342
2.8
617
2.1
2552
4.2
CBD
1765
14.5
6290
21.4
24039
39.1
Urban Residential
1597
13.2
4234
14.3
6955
11.3
Other
356
2.9
736
2.5
1183
1.9
Total
12140
100
29454
100
61436
6.2
Road Safety
Road safety Philosophy
Road safety philosophies generally express a long-term vision of an ideal road traffic system where
accidents and serious personal injury are virtually eliminated. Road "accidents" are not considered
accidental events that are the inevitable consequence of our demand for mobility; they are seen as
events that can be prevented. The main elements of road safety philosophies reflect generally well
known safety principles. People are fallible and make errors. Furthermore, people are physically
vulnerable and can only withstand a limited amount of external forces. Therefore, road safety
measures based on these philosophies and principles take account of these limitations and aim to
develop a road system that:
 Minimizes the chances of human error.
 Is forgiving of errors when they do occur.
 Prevents conflicts among road users with large differences in speed, mass and direction.
The WHO world report on traffic injury prevention (WHO, 2004) sets out a number of guiding
principles for road safety work which are based upon this line of thinking. It says, among other
things, that:
"Road crash injury is largely preventable and predictable; it is a human-made problem amenable to
rational analysis. Common driving errors and common pedestrian behavior should not lead to
death and serious injury – the traffic system should help users to cope with increasing demanding
conditions. The vulnerability of the human body should be the limiting design parameter for the
traffic system."
In line with these principles, a road traffic system that is safe and sustainable will have the
following features:
 its infrastructure will have been adapted to take into account human limitations, using
proper road design;
 its vehicles will be equipped to make the task of driving easier and to provide a high
standard of protection in crashes;
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 Its road users will be provided with adequate information and education and, where
appropriate, will be deterred from undesirable or dangerous behaviour.
 Incorporating safety features into road design
A key objective of safety engineering is to make drivers naturally choose to comply with the speed
limit. Through the use of self-explanatory road layouts, engineering can lead to safer road user
behaviour, as well as correcting defects in road design that otherwise may lead to crashes. In line
with this, a range of engineering measures are designed to encourage appropriate speed and
make hazards easily perceptible. These measures include:
 improved vertical alignment;
 advisory speed limits at sharp bends;
 regular speed-limit signs;
6.3
Road side Furniture and Road Markings
The various devices and road furniture used to control, guide, warning and regulate the traffic are
termed as traffic control devices. These features include the elements intended to improve the
driver's perception and comprehension of the continually changing appearance of the road. Hence,
they contribute to reduction of risk of occurrence of accidents. Widely used and the most common
types of traffic guide devices and furniture for road projects are:  Traffic sign,
 Road Marking
 Guide posts (Marker Posts) and Guard Rail
 Km post
The design of these facilities will be done in accordance with ERA guideline.
Traffic Signs
Traffic signs are of three general types:
Regulatory Signs: indicate legal requirements of traffic movement and are essential for all roads.
Warning Signs: indicate conditions that may be hazardous to highway users
Information Signs: convey information of use to the driver
Warning signs should be provided where there are unexpected changes in the driving conditions,
for example where:
The geometric standards for a particular class of road have been changed along a short section of
road, for example a sharp bend, a sudden narrowing of the road, or an unexpectedly steep
gradient;A bend occurs after a long section of straight road;There is an unexpected school
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crossing;A drift or other structure is not clearly visible from a safe distance;The driver is
approaching traffic calming measures such as speed hump.
Traffic signs have been provided, depending on the requirement, as per ERA's Standard
Specification 2014 and ERA's Standard Drawings 2014. Retro-reflective material engineering
grade material shall conform to the requirements of ASTM D 4956 or BS 873 Part 6,
Marker Posts (Guide Posts)
Marker posts have the function of controlling traffic to encourage safe operation of the road. There
are two types of marker posts: guideposts and kilometre posts. Guideposts are intended to make
drivers aware of potential hazards such as abrupt changes in shoulder width, abrupt changes in
the alignment, and approaches to structures etc. For changes in shoulder width and approaches to
structures, guide posts should be placed at appropriate intervals.
The required spacing of guideposts on curves according to ERA’s Geometric Design Manual-2013
is shown in Table below.
Table 6- 7: Guide post Spacing
Curve Radius (m)
Guide Post Spacing (m)
500
35
200
20
100
12
50
8
30
5
Route marker
KM posts are provided as per ERA standards at 1Km interval.
Safety barriers/Guardrails
Highway engineering safety is usually assumed to be optimized by linking geometric elements to a
design or operating speed, so that the resulting geometry has a consistency which reduces the
likelihood of a driver being presented with an unexpected situation. This concept of driver
expectation forms the basis of this set of design standards.
But it is not always practical or economical to provide safe slopes and curves within the standard in
all section of a road. In these instance safety barriers will be required and used.
Where appropriate, provision has been made to construct safety barriers from heavy masonry or
concrete or steel guardrails. High quality masonry work is found in Ethiopia and local communities
may benefit as a result of the labour-intensive construction method, wherever such barriers are to
be constructed. Safety barriers recommended to be installed on bridge approaches at least for
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50m on either ends and on hairpin curves. Heavy masonry guide walls(L=1.5m) recommended as
guideposts in high embankments more than 3m height for mountainous sections @ 15m spacing in
straight sections/ 5m on normal curves and 2m on substandard curves.
In addition, concrete safety barrier “New Jersey barrier will be used” as may be required during
detail design the type or selection will be done as per the standard. (Figure 6-1).
Figure 6- 3: Concrete/Masonry Barrier Detail
Steel Guard rail are recommended on all bridge approaches for a length of 50m on approaching
side and 25m on leaving side on both side.
.
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PAVEMENT DESIGN
7.1
Introduction
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The main function of a pavement is to carry traffic on a given road over the prevailing sub grade soil
in a given climate condition for a specified time interval (design period). The pavement structure
should therefore be structurally sound in order to serve the intended purpose for the given period
without premature failure. Construction of the pavement structure should also be economically viable
so that the construction of the road becomes feasible. This can be achieved by the use of best
combination of locally available materials. In light of this, analysis of the traffic characteristics of the
project area was carried out to determine the design traffic; and relevant data regarding the soil
foundation and construction material were assessed to determine the bearing strength of the sub
grade materials. The best economical combination of pavement layers (in relation to both thickness
and type of materials) that suit the underlying sub grade materials and the cumulative traffic to be
carried during the design life of the road is then determined. The appropriate pavement structures
are selected from Low volume roads (LVR) manual, 2011. Problematic soil stretches are also treated
with appropriate treatment measures. This report is therefore presents the activities carried out in
relation to the design of the Pavement structures of the project in detail.
7.2
Design Standards and Departure
7.2.1
Design Standards
This Report presents the pavement design of approximately 21km Road segments of the Project in
Chiro town. In the report, data required for design of the pavement are obtained from soils and
materials investigation and ERA Standard Technical Specification 2014, ERA Pavement Design
Manual 2013, ERA Low Volume Roads Manual 2011, AASHTO V1 -1993 Pavement Design Manual
and other pertinent design manuals.
7.2.2
Design Period
Design period is the period during which the proposed pavement carries the estimated design traffic
without major reconstruction works. Only routine and ordinary maintenance works is carried out to
maintain the road to its expected minimum performance level.
For most road projects, economic analysis period of between 10 and 20 years from the date of
opening is considered. For the subject project a design period of 20 years from the year the road is
opened to traffic i.e. (2028 - 2047) is considered for geometric design. The project road is expected
to be opened to traffic in the year 2028.
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Existing Pavement Condition Survey
The project road condition survey has been carried out by visual observations undertaken by means
of slow drive-over survey and supplemented with simple measurements. Visual assessment was
carried out by driving with a speed of not exceeding 15 km/hr. and stopping at various locations,
depending on variations in road conditions. The different distresses develop due to factors related to
sub grade soil, traffic, the type of material used for construction and climate of the area have been
identified. The extent and severity of each of the distresses was assesses and recorded. The
existing road is rated using the combination of the above distresses. Depending on the level of
damage, each sections of the road has been rated as very poor, fair and fair to good conditions. In
addition, measurement of width of the carriageway have been carried out.
The detailed site investigation along the alignment reveals that the existing gravel surface is
constructed from a silty sandy GRAVEL soil and the average width of the roadway is 4.0m-12.0m.
The existing road is accessible to four-wheel drive vehicles in all-weather condition except proposed
new alignment.
From the condition survey, it was noted that rutting, segregations, potholes, Erosions, and the use of
oversize dominated gravel wearing coarse, and absence of proper side drains are the major defects
of the road project. The frequency of occurrence and extent of the distresses vary from place to
place depending on the nature of the gravel wearing course, condition of the drainage system,
maintenance and nature of the sub grade soil, etc. The summary of the condition survey is
presented in in Appendix.
7.4
Traffic Volume
7.4.1
General
For effective planning and design of road projects, the knowledge of past, present and future traffic
movement on the proposed project road is essential. The volume and loading pattern of the current
and forecasted future traffic on any proposed road project constitutes the most important factor in
determining the feasibility of any planned road project, and in fixing design standards and in
estimating the construction and maintenance costs of road projects, as well. Hence, estimate of
current traffic and forecast of future traffic need to be carried out before any planning and design
work is undertaken.
Accordingly, Traffic Count and Origin-Destination (O-D) survey on Motorized and Non-motorized
traffic have been conducted for the project road as per the standard techniques outlined in the study
of Economic Feasibility and Detailed Engineering Design of road projects, as given in ERA standard
manual and other international standards.
7.4.2
Traffic Survey
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A traffic count on the proposed project road, Chiro Town Internal Asphalt Design project and the
road segments was conducted in end of April and Beginning of May 2023, which represents one of
the traffic count periods (cycle) of ERA, i.e., Cycle 2. The count includes motorized and nonmotorized traffic, and was carried out at identified stations along the project road segments.
Motorized and non-motorized Traffic counting was also conducted on existing adjacent road to
assess the traffic composition in the area, and estimate the volume of traffic that can distributed as
diverted traffic computation to the project road up on completion of the construction of the project.
The counts were made for 12 hours, from 6:00 am to 6:00 pm, for seven consecutive days; and night
counts were made for two days from 6:00 pm to 6:00 am, one of which is on a market day.
7.4.3
Traffic Survey Stations
In order to capture the current traffic on the proposed route of the project, traffic count consist of
motorized and non-motorized traffic were conducted at road segments as shown in the table below.
The following Table below summarize the traffic survey stations, road section, duration and purpose
of the Count.
Table 7- 1: Traffic Survey Stations, Road Section, Duration and Purpose of the Count
Survey
Station
type
Project
Location
Duration
Purpose
Method
Route
survey
Classified
Station
Road
Zone
7 day (+2 Traffic on the proposed Manual
Motorized
1
segment
Secretory
night)
road project corridor(For count
6 and 7
office
count
AADT-pavement design,
Count
economic
analysis,
Design standard...)
Station
Road
Wereda
7 day (+2 Traffic for the proposed Manual
2
segment
administration
night)
road project corridor to count
count
consider
2 and 3
as
a
continuous traffic And
Distribution
traffic
estimation
for
road
project
corridor(For
AADT-pavement design,
economic
analysis,
Design standard...)
Station
For
all hiro
3(Major
Road
road)
segment
general 7 day (+2
hospital
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Station
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Location
Duration
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Purpose
Method
Route
survey
AADT-pavement design,
economic
analysis,
Design standard...)
Station
Road
JFM
7 day (+2 Traffic for the proposed Manual
4
segment
petroleum
night)
road project corridor to count
count
consider
4,5
and
1,9,8
as
a
continuous traffic (For
AADT-pavement design,
economic
analysis,
Design standard...)
7.4.4
Vehicle Classification
For detailed engineering design purpose, vehicles were classified into passenger and freightdepending on the type of service they render. Passenger vehicles were further classified into Car,
Land Rover, Small Bus, Medium Bus and Large Bus, and freight vehicles were classified as Small
Trucks, Medium Trucks, Heavy Trucks and Truck Trailer based on their respective capacity to carry
load and in accordance with ERA’s Vehicle Classification System. Accordingly, nine vehicle
categories were used for the purpose of road side traffic count as listed below.
Table 7- 2: Vehicle Classification
Vehicle Type
Description
Car
Small automobiles
Land Rover
4WD and utility vehicles
Small Bus
Passenger cars up to 25 seats.
Medium Bus
Passenger cars above 25 seats and below 45 seats
Large Bus
Passenger cars above 45 seats.
Small Truck
Light goods vehicles and delivery vans up to 3.5 tons load.
Medium Truck
Goods vehicle with 3.5 – 7.5 tons load.
Heavy Truck
Trucks above 7.5 tons load.
Truck and Trailer
Trucks with trailer or semi-trailer and Tanker trailer.
7.4.5
Traffic Count and Analysis
Motorized Traffic Count (Day Time)
As discussed above, Motorized Traffic Count was conducted for Seven days (12 hours) during day
time at the stations mentioned above. The volume of traffic obtained is then summed up to get the
total number of traffic in the week, and then divided by seven to obtain the average daily day time
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traffic. See table 7.3 to 7.6 below gives the sum and average of seven days’ traffic by vehicle
category at the respective station count location.
Table 7- 3: Day Time Traffic Count Survey Result: Station 1
Day count (Chiro Town Administration-Mtichu) Both directions sum @ st-1 survey location (7 days day count)
Day Date
Car
4WD
Bajaj
S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck
Track
Trailer
Total
1
28/04/2023 0
59
283
0
0
1
1
0
0
0
344
2
29/04/2023 0
30
347
0
0
0
11
4
2
0
394
3
30/04/2023 2
29
312
4
0
0
0
1
0
0
348
4
05/01/23
2
28
336
0
0
0
4
3
1
0
374
5
05/02/23
0
21
340
6
0
0
0
0
4
0
371
6
05/03/23
0
22
343
0
0
0
5
0
1
0
371
7
05/04/23
1
57
579
5
2
1
12
1
3
0
661
Total
5
246
2540
15
2
2
33
9
11
0
2863
Average
1
35
363
2
0
0
5
1
2
0
409
Table 7- 4: Day Time Traffic Count Survey Result: Station 2
Day count (Chiro Wereda Office-Chiro Peace Mosque) Both directions sum @ st-2 survey location (7 days day
count)
Car
4WD Bajaj
S/Bus M/Bus L/Bus S/Truck
M/Truck H/Truck Track
Total
Trailer
Day Date
1
28/04/2023 45
373
5856
143
46
14
56
8
19
0
6560
2
29/04/2023 48
500
9900
141
66
32
68
23
6
3
10787
3
30/04/2023 44
498
8990
147
62
12
47
16
11
1
9828
4
05/01/23
52
711
7400
318
127
40
95
28
10
4
8785
5
05/02/23
58
573
8010
215
61
23
86
24
22
2
9074
6
05/03/23
104
900
10099 451
200
46
127
49
25
9
12010
7
05/04/23
150
1167 6902
729
197
92
162
59
22
24
9504
Total
501
4722 57157 2144
759
259
641
207
115
43
66548
Average
72
675
108
37
92
30
16
6
9507
8165
306
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Table 7- 5: Day Time Traffic Count Survey Result: Station 3
Day count (Chiro town -Addis Ababa) Both directions sum @ st-3 survey location (7 days day count)
Car
Day Date
4WD
Bajaj
S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck
Track
Trailer
Total
1
28/04/2023 51
666
2401
214
119
41
84
175
57
897
4705
2
29/04/2023 91
814
4500
240
224
56
99
108
63
558
6753
3
30/04/2023 61
762
4499
222
231
46
144
100
77
614
6756
4
05/01/23
53
618
4414
277
220
54
96
59
71
469
6331
5
05/02/23
34
523
5140
307
195
66
114
69
155
353
6956
6
05/03/23
31
549
5280
245
195
81
187
111
187
390
7256
7
28/04/2023 51
555
6860
208
149
89
146
103
146
1137
9444
Total
372 4487 33094 1713
1333
433
870
725
756
4418
48201
Average
53
190
62
124
104
108
631
6886
641
4728
245
Table 7- 6: Day Time Traffic Count Survey Result: Station 4
Day count (Agape Hotel-Agri Reserch Center) Both directions sum @ st-4 survey location (7 days day count)
Car
4WD
Day Date
Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck
Track
Trailer
Total
1
28/04/2023 22
51
376
23
2
1
13
11
6
1
506
2
29/04/2023 46
44
363
16
1
0
12
7
6
0
495
3
30/04/2023 11
47
362
15
7
3
15
9
6
0
475
4
05/01/23
18
81
339
12
2
0
6
4
5
0
467
5
05/02/23
5
78
398
11
1
0
10
5
4
0
512
6
05/03/23
1
75
342
2
3
0
7
1
2
0
433
7
05/04/23
20
83
320
27
7
1
16
17
4
0
495
Total
123 459
2500 106
23
5
79
54
33
1
3383
Average
18
357
3
1
11
8
5
0
483
66
15
Night Time Motorized Traffic Count
Likewise, Motorized Traffic Count was conducted for two days (12 hours) during night time at the
stations mentioned above. The volume of traffic obtained is then summed up to get the total number
of traffic in the two days, and then divided by two to obtain the average daily night time traffic. See
Table 7.7 and 7.10 below gives the sum and average of the two days’ traffic by vehicle category at
the respective station count location.
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Table 7- 7: Night Time Traffic Count Survey Result: Station 1
Night count (Chiro Town Administration-Mtichu )Both direction @ Station 1 survey location (2 days night
count)
Car 4WD Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track
Total
Trailer
Day Date
1
30/04/2023 0
7
78
1
0
0
0
1
0
0
87
2
02/05/2023 0
5
85
2
0
0
0
0
1
0
93
Table 7- 8: Night Time Traffic Count Survey Result: Station 2
Night count (Chiro Wereda Office-Chiro Peace Mosque) Both direction @ Station 2 survey location (2 days
night count)
Car 4WD Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track
Total
Trailer
Day Date
1
30/04/2023 10
108
816
34
10
0
9
2
2
1
992
2
05/02/2023 15
73
1191 44
9
1
19
5
1
2
1360
Table 7- 9: Night Time Traffic Count Survey Result: Station 3
Night count (Chiro town -Addis Ababa) Both direction @ Station 3 survey location (2 days night count)
Car
4WD Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track
Total
Trailer
Day Date
1
30/04/2023 22
179
902
124
54
18
73
99
67
185
1723
2
05/02/2023 17
121
1010 183
35
19
95
63
66
120
1729
Table 7- 10: Night Time Traffic Count Survey Result: Station 4
Night count (Agape Hotel-Agri Reserch Center) Both direction @ Station 4 survey location (2 days night
count)
Car 4WD Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track
Total
Trailer
Day Date
1
30/04/2023 4
17
26
14
3
0
4
0
3
0
71
2
05/02/2023 2
13
6
6
7
0
6
2
2
0
44
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Night Factor (NF)
Night factor is computed by dividing the average 24-hour traffic of the two days when the night time
traffic has been count by 12-hour day time traffic of the same days. See table 1.11 to .1.14 below
gives the Night Factor by vehicle category at the respective station count location.
Table 7- 11: Night Factor: Station 1
Night factor @ station 1
Car
Date
4WD Bajaj
S/Bus M/Bus L/Bus
M/Truck H/Truck Track
S/Truck
Trailer
Shift
Total
30/04/2023 Day
2
29
312
4
0
0
0
1
0
0
348
Night
0
7
78
1
0
0
0
1
0
0
87
2
36
390
5
0
0
0
2
0
0
435
Day
0
21
340
6
0
0
0
0
4
0
371
Night
0
5
85
2
0
0
0
0
1
0
93
0
26
425
8
0
0
0
0
5
0
464
24hrs 1
31
408
7
0
0
0
1
3
0
450
Total
2/05/2023
Total
Average
count
Determination of Average Day Time count (2 days)
30/04/2023 Day
2
29
312
4
0
0
0
1
0
0
348
2/05/2023
0
21
340
6
0
0
0
0
4
0
371
1
25
326
5
0
0
0
1
2
0
360
1.25
1.30
1.00
1.00
1.00
2.00
1.25
1.00
Day
Average Day Time
Traffic (7day)
Night Factor
1.00 1.24
Table 7- 12: Night Factor: Station 2
Night factor @ station 2
Car
Date
H/Truck Track
Trailer
Shift
30/04/2023 Day
Total
44
498
8990 147
62
12
47
16
11
1
9828
Night 10
108
816
34
10
0
9
2
2
1
992
54
606
9806 181
72
12
56
18
13
2
10820
58
573
8010 215
61
23
86
24
22
2
9074
Total
2/05/2023
4WD Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck
Day
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Night factor @ station 2
Car
Date
4WD Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck
H/Truck Track
Trailer
Shift
Night 15
73
1191 44
9
1
19
5
1
2
1360
73
646
9201 259
70
24
105
29
23
4
10434
24hrs 64
626
9504 220
71
18
81
24
18
3
10627
Total
Average
Total
count
Determination of Average Day Time count (2 days)
30/04/2023 Day
44
498
8990 147
62
12
47
16
11
1
9828
2/05/2023
58
573
8010 215
61
23
86
24
22
2
9074
51
536
8500 181
62
18
67
20
17
2
9451
1.12
1.15
1.03
1.21
1.18
1.09
2.00
Day
Average day time
count(B)
Night factor(A/B)
1.25 1.17
1.22
Table 7- 13: Night Factor: Station 3
Night factor @ station 3
Car
Date
H/Truck Track
Trailer
Shift
30/04/2023 Day
2/05/2023
Total
61
762
4499 222
231
46
144
100
77
614
6756
Night 22
179
902
124
54
18
73
99
67
185
1723
83
941
5401 346
285
64
217
199
144
799
8479
34
523
5140 307
195
66
114
69
155
353
6956
Night 17
121
1010 183
35
19
95
63
66
120
1729
51
644
6150 490
230
85
209
132
221
473
8685
67
793
5776 418
258
75
213
166
183
636
8582
Total
Day
Total
Average
4WD Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck
24hrs
count
Determination of Average Day Time count (2 days)
30/04/2023 Day
61
762
4499 222
231
46
144
100
77
614
6756
2/05/2023
34
523
5140 307
195
66
114
69
155
353
6956
48
643
4820 265
213
56
129
85
116
484
6856
1.20
1.21
1.33
1.65
1.96
1.57
1.32
1.41
Day
Average Day Time
Traffic (7day)
Night Factor
1.41 1.23
1.58
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Table 7- 14: Night Factor: Station 4
Night factor @ station 4
Car
Date
4WD Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck
H/Truck Track
Trailer
Shift
30/04/2023
Day
11
47
362
15
7
3
15
9
6
0
475
Night 4
17
26
14
3
0
4
0
3
0
71
15
64
388
29
10
3
19
9
9
0
546
5
78
398
11
1
0
10
5
4
0
512
Night 2
13
6
6
7
0
4
2
2
0
42
7
91
404
17
8
0
14
7
6
0
554
11
78
396
23
9
2
17
8
8
0
550
Total
2/05/2023
Day
Total
Average
Total
24hrs
count(A)
Determination of Average Day Time count (2 days)
30/04/2023 Day
11
47
362
15
7
3
15
9
6
0
475
1/05/2023
5
78
398
11
1
0
10
5
4
0
512
8
63
380
13
4
2
13
7
5
0
494
1.04
1.77
2.25
1.00
1.32
1.14
1.50
1.00
Day
Average day time
count(B)
Night factor(A/B)
1.38 1.24
Motorized Average Daily Traffic (ADT)
The ADT at each traffic count station can then be computed by multiplying the average day time
traffic by night factor, as given in Table 3-15 above. 3-18 below summarizes the ADT at the station
count location.
Table 7- 15: Motorized Average Daily Traffic (ADT): Station 1
Average daily traffic @ Station 1 survey location
Car
4WD Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track
Total
Trailer
Average Day Time
Traffic (7day)
Night factor
1
35
363
2
0
0
5
1
2
0
1.00
1.24
1.25
1.30
1.00
1.00
1.00
2.00
1.25
1.00
44
454
3
0
0
5
3
2
0
Average daily time 1
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Average daily traffic @ Station 1 survey location
Car
4WD Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track
Total
Trailer
(ADT)
Table 7- 16: Motorized Average Daily Traffic (ADT): Station 2
Average daily traffic @ Station 2 survey location
Car
4WD Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track
Total
Trailer
Average Day Time
Traffic (7day)
Night factor
Average daily time
(ADT)
72
675
8165 306
108
37
92
30
16
6
1.25
1.17
1.12
1.22
1.15
1.03
1.21
1.18
1.09
2.00
89
789
9129 372
125
38
111
35
18
12
9507
10718
Table 7- 17: Motorized Average Daily Traffic (ADT): Station 3
Average daily traffic @ Station 3 survey location
Car
4WD Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track
Total
Trailer
Average
Time
Day
Traffic 53
641
4728 245
190
62
124
104
108
631
1.41
1.23
1.20
1.58
1.21
1.33
1.65
1.96
1.57
1.32
75
791
5666 387
230
82
205
203
170
830
6886
(7day)
Night factor
Average
daily
time (ADT)
8639
Table 7- 18: Motorized Average Daily Traffic (ADT): Station 4
Average daily traffic @ Station 4 survey location
Car
4WD Bajaj S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track
Total
Trailer
Average
Time
Day
Traffic
18
66
357
15
3
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(7day)
Night factor
Average
daily
time (ADT)
1.38
1.24
1.04
1.77
2.25
1.00
1.32
1.14
1.50
1.00
24
81
372
27
7
1
15
9
7
0
543
Non -Motorized Traffic (Day Time)
Non-Motorized Traffic Count was also conducted for Seven days (12 hours) during day time at the
stations mentioned above. The volume of traffic obtained is then summed up to get the total number
of traffic in the week, and then divided by seven to obtain the average daily day time traffic. table 319 to 3-22 below gives the sum and average of seven days’ traffic by vehicle category at the station
count location.
Table 7- 19: Day Time Non-motorized Traffic survey result: Station 1
Motorcycle
Animal Cart
Date
Total
28/04/2023
17
0
17
29/04/2023
29
0
29
30/04/2023
23
0
23
05/01/23
20
0
20
05/02/23
28
0
28
05/03/23
41
0
41
05/04/23
43
0
43
Total
201
0
201
Average
29
0
29
Table 7- 20: Day Time Non-motorized Traffic survey result: Station 2
Motorcycle
Animal Cart
Date
28/04/2023
29/04/2023
30/04/2023
05/01/23
05/02/23
05/03/23
05/04/23
Total
Average
Total
119
132
101
155
256
292
650
1705
244
20
44
48
41
33
82
61
329
47
139
176
149
196
289
374
711
2034
291
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Table 7- 21: Day Time Non-motorized Traffic survey result: Station 3
Motorcycle
Animal Cart
Date
Total
28/04/2023
10
333
323
29/04/2023
4
180
176
30/04/2023
18
127
109
05/01/23
6
111
105
05/02/23
8
138
130
05/03/23
3
87
84
05/04/23
161
1
162
Total
1088
50
1138
Average
155
7
163
Table 7- 22: Day Time Non-motorized Traffic survey result: Station 4
Motorcycle
Animal Cart
Date
Total
28/04/2023
45
0
45
29/04/2023
83
0
83
30/04/2023
74
0
74
05/01/23
90
0
90
05/02/23
71
1
72
05/03/23
44
1
45
05/04/23
73
5
78
Total
201
0
487
Average
69
1
70
Non -Motorized Traffic (Night Time)
Likewise, Non-Motorized Traffic Count was conducted for two days (12 hours) during night time at
the stations mentioned above. The volume of traffic obtained is then summed up to get the total
number of traffic in the two days, and then divided by two to obtain the average daily night time
traffic. table 3-23 to 3-26 below gives the sum and average of the two days’ traffic by NMT category
at the respective road sections.
Table 7- 23: Night Time Non-motorized Traffic survey result: Station 1
Motorcycle
Night
Animal Cart
Date
Total
30/04/2023
11
0
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Table 7- 24: Night Time Non-motorized Traffic survey result: Station 2
Motorcycle
Animal Cart
Date
Total
Night
30/04/2023
13
4
17
02/05/2023
22
1
23
Table 7- 25: Night Time Non-motorized Traffic survey result: Station 3
Motorcycle
Animal Cart
Date
Total
Night
30/04/2023
8
4
12
02/05/2023
26
0
26
Table 7- 26: Night Time Non-motorized Traffic survey result: Station 4
Motorcycle
Animal Cart
Date
Total
Night
30/04/2023
9
0
9
02/05/2023
5
0
5
Night Factor (NF) Computation
Night factor is computed by dividing the total 24-hour traffic by 12-hour day time traffic. Tables below
gives the Night Factor by NMT category at the respective road sections.
Night factor is computed by dividing the total 24-hour traffic by 12-hour day time traffic. table 3-27to
3-30 below gives the Night Factor by NMT category at the respective road sections.
Table 7- 27: Night Factor: @ station 1
Motorcycle
Date
30/04/2023
Animal Cart
Shift
Total
Day
23
Night
11
0
0
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Animal Cart
Shift
Total
Total
34
0
34
Day
28
0
28
night
14
0
14
Total
42
0
42
Average 24 hrs. count
38
0
38
30/04/2020 Day
23
10
23
02/05/2020 Day
28
10
28
Average Day Time Count
26
0
26
Average 24 hrs. count
38
0
26
Average Day Time Count
26
0
26
Night Factor
1.49
1
02/05/2023
Table 7- 28: Night Factor: @ station 2
Motorcycle
Date
Animal Cart
Shift
Total
Day
101
48
149
Night
13
4
17
114
52
166
Day
256
33
289
night
22
1
23
Total
278
34
312
Average 24 hrs. count
196
43
239
30/04/2020 Day
101
48
149
02/05/2020 Day
256
33
289
Average Day Time Count
179
43
219
Average 24 hrs. count
196
43
239
Average Day Time Count
179
43
219
Night Factor
1.1
1.06
30/04/2023
Total
02/05/2023
Table 7- 29: Night Factor: @ station 3
Motorcycle
Date
Animal Cart
Shift
Total
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Animal Cart
Shift
Total
Day
109
18
127
Night
8
4
12
117
22
139
Day
130
8
138
Night
26
0
26
Total
156
8
164
Average 24 hrs. count
137
15
152
30/04/2023 Day
109
18
127
02/05/2023 Day
130
8
138
Average Day Time Count
120
13
133
Average 24 hrs. count
137
15
152
Average Day Time Count
120
13
133
Night Factor
1.14
1.15
30/04/2020
Total
02/05/2020
Table 7- 30: Night Factor: @ station 4
Motorcycle
Date
Animal Cart
Shift
Total
Day
74
0
74
Night
9
0
9
83
0
83
Day
71
1
72
night
5
0
5
Total
76
1
77
Average 24 hrs. count
80
1
80
30/04/2023 Day
74
0
74
02/05/2023 Day
71
1
72
Average Day Time Count
73
1
73
Average 24 hrs. count
80
1
80
Average Day Time Count
73
1
73
Night Factor
1.10
1
30/04/2025
Total
02/05/2023
Non-Motorized Average Daily Traffic
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The ADT at each traffic count station can then be computed by multiplying the average day time
traffic by night factor as given in table 3-31 above. table 3-34 below summarizes the ADT at the
respective stations.
Table 7- 31: Non-Motorized Average Daily Traffic (ADT)-Station 1
Station 1 Average Daily Traffic
motorcycle
Animal Cart
Total
0
29
Average Day time count (7day) 29
0
1.49
Night Factor
0
43
43
Average Daily Traffic (ADT)
Table 7- 32: Non-Motorized Average Daily Traffic (ADT)-Station 2
Station 2 Average Daily Traffic
motorcycle
Animal Cart
Total
47
291
Average Day time count (7day) 244
1.10
1.06
Night Factor
267
317
Average Daily Traffic (ADT)
50
Table 7- 33: Non-Motorized Average Daily Traffic (ADT)-Station 3
Station 3 Average Daily Traffic
motorcycle
Animal Cart
Total
7
163
Average Day time count (7day) 155
1.14
1.15
Night Factor
178
186
Average Daily Traffic (ADT)
8
Table 7- 34: Non-Motorized Average Daily Traffic (ADT)-Station 4
Station 4 Average Daily Traffic
motorcycle
Animal Cart
Total
1
70
Average Day time count (7day) 69
1.10
1.00
Night Factor
75
76
Average Daily Traffic (ADT)
1
Modal Shift (From Non-Motorized to Motorized Traffic)
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7.4.5.9.1 Assumptions for converting Non -Motorized Traffic to Motorized traffic
A. Freight Traffic
Animal carts are commonly used in the project area to bring various freight products to market
centers. Most of this traffic will transfer to vehicular traffic once the proposed road is opened to traffic.
Considering the fact that the proposed road project is in a poor condition and the community in the
project area have been suffering from lack of proper road infrastructure, it is envisaged that most of
the current non-motorized mode of transport will divert to motorized mode of transport. Considering
the current road condition which deprived motorized vehicles to use the road, and status of the
socio-economic profile of the area, it is assumed that 50% of the current non-motorized freight traffic
may shift to motorized freight traffic within one to two years of opening of the project road to traffic.
It is also assumed that a national average of 80 kg for a unit of animal-based freight transport (ABFT)
and 400kg for a unit of animal cart freight (ACFT) can be considered for the prediction of the volume
of motorized freight traffic.
Furthermore, from the traffic composition of the project road it is noted that small trucks are the main
means of freight transport, and hence the non-motorized freight traffic is expected to be converted to
small trucks.
B. Passenger Traffic
Similarly, considering the facts mentioned above for freight transport, it is assumed that 50% of the
current non-motorized passenger movement(motorcycles) may shift to motorized traffic within one to
two years of opening of the project road to traffic.
In estimating number of passengers, the motorcycles are assumed to carry 1.5 passengers per
motorcycle, as some motorcycles are observed to carry 1 passenger and some carry 2 passengers.
From the traffic composition of the project road, it is noted that medium buses are the main means of
passenger transport, and hence the non-motorized passenger traffic is expected to be converted to
medium busses.
Using the above assumptions, the volume of motorized traffic has been computed as shown in the
following.
Table 7- 35: Modal shift Traffic
Car 4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track Trailer
Total
0
2
Location
Station 1
0
0
2
0
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0
0
0
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Station 2
0
0
0
8
0
3
0
0
0
11
Station 3
0
0
0
5
0
1
0
0
0
6
Station 4
0
0
0
3
0
1
0
0
0
4
Summary of Normal Traffic
Normal Traffic is the current traffic on the road which includes motorized and non-motorized traffic,
which are obtained by direct count on the project road. Based on ERA geometric design manual to
defined the design standard purpose three-wheeler(bajaj) is converted to passenger car unit
(PCU=0.4*Bajaj). The following gives the summary of the traffics.
Table 7- 36: Summary of Normal Traffic – Station 1
Station-1- Determination of Normal Traffic
Car
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track
+Bajaj
Total
Trailer
Converted
to PCU
Average Daily
182
44
3
0
0
Traffic (ADT)
Modal Shift
0
0
0
2
0
ADT + Modal
182
44
3
2
0
Shift
Table 7- 37: Summary of Normal Traffic – Station 2
5
3
2
0
238
0
0
0
0
2
5
3
2
0
240
Station-2- Determination of Normal Traffic
Car
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track
+Bajaj
Total
Trailer
Converted
to PCU
Average Daily
3741
789
372
125
38
Traffic (ADT)
Modal Shift
0
0
0
8
0
ADT + Modal
3741
789
372
133
38
Shift
Table 7- 38: Summary of Normal Traffic – Station 3
111
35
18
12
5241
3
0
0
0
11
114
35
18
12
5252
Station-3- Determination of Normal Traffic
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4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track
+Bajaj
Total
Trailer
Converted
to PCU
Average Daily
2341
791
387
230
82
Traffic (ADT)
Modal Shift
0
0
0
5
0
ADT + Modal
2341
791
387
235
82
Shift
Table 7- 39: Summary of Normal Traffic – Station 4
205
203
170
830
5239
1
0
0
0
6
206
203
170
830
5245
Station-4- Determination of Normal Traffic
Car
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track
+Bajaj
Total
Trailer
Converted
to PCU
Average Daily
173
81
27
7
Traffic (ADT)
Modal Shift
0
0
0
3
ADT + Modal
173
81
27
10
Shift
Origin Destination (O-D) Survey
1
15
9
7
0
320
0
1
0
0
0
4
1
16
9
7
0
324
Diverted traffic computed on the project road segments by assuming the traffic distribution on the
town as road network. The potential diverted traffic is computed from parallel adjacent existing route
as road network the traffic will be distributed.
Table 7- 40: Potential Distributed Traffic to the project roads assumptions
Traffic
station
TC 2
TC 3
TC 4
Distribution
Direction
Chiro
Wereda
% of distribution
S-2
20% Passenger Car and 40% trucks
Office- S-3
Chiro Peace Mosque
Chiro town -Addis ababa
Agape
road segments
20%
S-1-1
20%
S-1-2
30%
S-5
10% for Passenger car, Small and medium truck
S-1-1
50%
Hotel-Agri
Reserch Center
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Table 7- 41: Potential Distributed Traffic to the project roads from Station 2 (Wereda Administration)
Road segment 2
Source; Consultant
Table 7- 42: Potential Distributed Traffic to the project roads from Station 2 (Wereda Administration)
Road segment 3
Table 7- 43: Potential Distributed Traffic to the project roads from Station 2 (Wereda Administration)
Road segment 1-1
Table 7- 44: Potential Distributed Traffic to the project roads from Station 2 (Wereda Administration)
Road segment 1-2
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Table 7- 45: Potential Distributed Traffic to the project roads from Station 4 (Agape Hotel) Road
segment 1-1
Source; Consultant
Table 7- 46: Potential Distributed Traffic to the project roads from Station 3(Main trunk road)
Source; Consultant
7.4.6
Generated Traffic
Normal Generated Traffic
Once the project road is realized, it is assumed that the traffic to be generated is triggered by
decrease in transport cost subsequent to the improvement in the condition of the road. The
improvement which involves improvement in geometric and pavement feature of the road, are
expected to result in increased demand for transportation, and hence more vehicles will be induced
to the project road.
The existing road along the project route is in very poor condition. Considering the current situation,
the construction of the project road is expected to stimulate generation of trips in vehicular transport
which will enhance access to markets and various service centres in the vicinity of the project.
The recommended approach to forecasting generated traffic is to use demand relationships which
show how traffic increases as the cost of a journey decreases. Studies carried out in similar
countries give an average for the price elasticity of demand for transport of about -1.0. This means
that a one per cent decrease in transport costs leads to a one per cent increase in traffic. This is
extra traffic over and above the increase in normal traffic.
However, Handy and Boarnet (2014) performed a critical evaluation of various induced travel studies
and found that short-run elasticity effect of road development generally range from 0.3 to 0.6.
(Generated Traffic and Induced Travel Implication for Transport Planning, 2015).
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The estimation of generated traffic is based on estimating the shape of the demand function, which
is expressed as an elasticity of demand. It shows the responsiveness of demand to a change in cost,
which in turn is a response of change in the travel time. In the case of generated traffic, the demand
for transport is related to expected reductions in journey costs and travel time. For this analysis,
savings in travel time is used to determine the percent of generated traffic based on travel time with
and without the project using the formula: seasonal factor
Generated Traffic Factor = β [(Cijp / Cijb) – 1]
Where:
β is the elasticity;
Cijp is the with-project travel cost;
Cijb is the base case, without project travel cost;
Table 7- 47: Travel time to estimate Generated Traffic Factor
Without Project
With Project
Length
Speed1
Travel
Station
(km)
(km/hr )
(min)
Station 1
2.31
20
Station 4
0.588
20
Time Length
Speed1
Travel Time
(km)
(km/hr )
(min)
6.93
2.31
50
3
1.764
0.588
50
1
Table 3-47: Station 1-Estimate of Generated Traffic Factors from the travel time
With Project (Upgrading of existing Road
Station
Station 1
Parameter
to gravel Road)
Low
Medium
High
β (elasticity)
-0.3
-0.45
-0.6
Cijp (time in minutes)
3
3
3
Cijb (time in minutes)
6.93
6.93
6.93
Generated Traffic Factor (GTF)
0.18
0.27
0.36
The above shows that the generated traffic factor is 0.18 for low scenario, 0.27 for medium scenario
and 0.36 for high scenario.
Table 7- 48: Station 4-Estimate of Generated Traffic Factors from the travel time
With Project (Upgrading of existing
Road Section
Parameter
β (elasticity)
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Medium
High
-0.3
-0.45
-0.6
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Cijp (time in minutes)
1
1
1
Cijb (time in minutes)
1.764
1.764
1.764
Generated Traffic Factor (GTF)
0.18
0.27
0.36
The above shows that the generated traffic factor is 0.18 for low scenario, 0.27 for medium scenario
and 0.36 for high scenario.
Traffic generation also depends on the economic activity in the area, and the level of development
and the status of the living condition of the people in the area. If the economic activity is low, and the
development and living condition of the people in the area is in low level, the demand for
transportation will be less. Considering the current development level of the project area, it is
envisaged that the level of traffic generation falls in the medium to high scenario. Hence, it is
assumed that 27 % of normal traffic volume will generate within four to five years of the opening of
the project.
Table 7- 49: Station 1-Potential Generated Traffic for Project Road (taking medium scenario)
ADT, Station 1
Generated
traffic 27%
Car
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track Trailer
Total
182
44
3
2
0
5
3
2
0
240
49
12
1
1
0
1
1
1
0
65
Table 3- 50: Station 4-Potential Generated Traffic for Project Road (taking medium scenario)
ADT, Station 4
Generated
traffic 27%
Car
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track Trailer
Total
173
81
27
10
1
16
9
7
0
324
47
22
7
3
0
4
2
2
0
88
Seasonal Conversion Factor
The ADT computed from the traffic count conducted by the Consultant represent the traffic
movement on the existing adjacent roads during the time of traffic count, which is at End of April and
Beginning of May 2023. However, this ADT does not show the annual average daily traffic
movement on the project road in a particular year. Traffic volumes can have large daily, weekly,
monthly and seasonal variations. Variation from month to month (seasonal variation) can be
minimized by repeating the weekly traffic count at intervals during a year. For this purpose, ERA is
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conducting traffic count at all traffic count stations in the country three times a year. The seasonal
conversion factor is therefore calculated from the data obtained from ERA for Mieso to Asebe Teferi
project road and the ADT is adjusted accordingly to take the seasonal variation into account. The
following give the average annual daily traffic and the average daily traffic at cycle 2 of ERA annual
traffic count cycle on Mieso to Asebe Teferi project road 2014,2015, 2017,2019 & 2020 by vehicle
class. The traffic count was conducted in the month of End of April and Beginning of May 2023.,
which falls in the second cycle of ERA’s yearly traffic count. Hence, the seasonal conversion factor
has been calculated with reference to the second cycle by dividing the average AADT by the
average third cycle.
Table 7- 50: Seasonal Conversion Factor
Mieso to Asebe Teferi
2014
Cars
LDV
S/Bus
L/Bus
S/Truck
M/Truck
H/Truck
T&T
Cycle 1
40
154
242
72
128
227
106
98
1067
Cycle 2
11
95
334
125
103
213
138
206
1225
Cycle 3
16
103
221
83
126
118
111
89
867
AADT 2014
22
117
266
93
119
186
118
131
1053
2015
Cars
LDV
S/Bus
L/Bus
S/Truck
M/Truck
H/Truck
T&T
Cycle 1
23
229
233
76
180
149
142
131
1163
Cycle 2
27
210
269
90
161
140
119
109
1125
Cycle 3
27
210
269
90
161
140
119
109
1125
AADT 2015
26
216
257
85
167
143
127
116
1138
2017
Cars
LDV
S/Bus
L/Bus
S/Truck
M/Truck
H/Truck
T&T
Cycle 1
22
121
209
124
190
208
212
157
1243
Cycle 2
29
118
156
100
128
132
69
100
832
Cycle 3
22
73
101
51
80
102
137
234
800
AADT 2017
24
104
155
92
133
147
139
164
958
2019
Cars
LDV
S/Bus
L/Bus
S/Truck
M/Truck
H/Truck
T&T
Cycle 1
31
110
375
198
134
230
399
770
2247
Cycle 2
36
271
294
135
210
137
226
562
1871
Cycle 3
21
83
137
45
100
180
146
217
929
AADT 2019
29
155
269
126
148
182
257
516
1682
2020
Cars
LDV
S/Bus
L/Bus
S/Truck
M/Truck
H/Truck
T&T
Cycle 1
15
94
183
57
93
163
62
168
835
Cycle 2
15
94
183
57
93
163
62
168
835
Cycle 3
52
284
345
128
293
334
368
591
2395
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AADT 2020
27
157
237
81
160
220
164
309
1355
Average (AADT)
26
150
237
95
145
176
161
247
1237
Average Cycle-2
22
158
258
106
151
172
151
240
1260
0.95
0.92
0.90
0.96
1.02
1.06
1.03
SCF = Av. AADT/Av. Cycle 1.16
2 traffic
AADT of the Project Road at 2020 (AADT0)
AADT is the Annual Average Traffic for a particular road, and is obtained by multiplying the ADT
obtained from actual traffic count for a week by the SCF.
Table 7- 51: AADT of the Normal Traffic at 2023–Station 1
Car
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track Trailer
Total
182
44
3
2
0
5
3
2
0
240
49
12
1
1
0
1
1
1
0
65
ADT(NT+DT+GT) 231
55
4
3
0
6
3
2
0
305
SCF
1.16
0.95
0.92
0.91
0.90
0.96
1.02
1.06
1.03
AADT
269
52
3
3
0
6
3
3
0
Normal Traffic
Normal
Generated Traffic
339
Table 7- 52: AADT of the Normal Traffic at 2023–Station 4
Car
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track Trailer
Total
173
81
27
10
1
16
9
7
0
324
47
22
7
3
0
4
2
2
0
88
ADT(NT+DT+GT) 220
103
34
13
1
20
11
9
0
412
SCF
1.16
0.95
0.92
0.91
0.90
0.96
1.02
1.06
1.03
AADT
255
98
31
12
1
19
11
10
0
Normal Traffic
Normal
Generated Traffic
7.4.7
Traffic Growth and Forecast
Design Period
Design period is the period during which the proposed pavement carries the estimated design traffic
without major reconstruction works. Only routine and ordinary maintenance works is carried out to
maintain the road to its expected minimum performance level.
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For most road projects, economic analysis period of between 10 and 20 years from the date of
opening is considered. For the subject project a design period of 20 years from the year the road is
opened to traffic i.e. (2028 - 2047) is considered for geometric design. The project road is expected
to be opened to traffic in the year 2028.
Table 7- 53: Schedule for Implementation of the Project
Activity
Period
Completion of Detail Design and tender process.
End of 2023
Construction (5 years starting Beginning of 2024)
2024-2027
Completion of the construction
End of 2027
Open for traffic
Beginning of 2028
Design Period (20 years)
2028-2047
Traffic Growth Rate
7.4.7.2.1 Base year Traffic (at 2028) – AADT0
Base year traffic is the traffic that will use the project road at the first year of the opening of the road
to traffic. It includes normal, diverted, generated and development induced traffics. It is obtained by
forecasting the above-mentioned traffic to the base year by using the growth rate established above.
The following gives the base year traffic at 2028.
Table 7- 54: Base year Traffic (at 2028) - AADT1 – Station 1(Road segment 6&7)
AADT0 2023
Growth
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track Trailer
Total
269
52
3
3
0
6
3
3
0
339
9.72
9.72
9.31
9.31
9.31
9.99
9.99
9.99
10.11
8.81
8.81
8.68
8.68
8.68
8.99
8.99
8.99
9.1
670
131
8
7
1
14
8
7
0
rate
(2015-2025)
Growth
Car
rate
(2026-2047)
AADT0 at 2028
845
Table 7- 55: Base year Traffic (at 2028) - AADT1 – Station 2 (Road segment 2)
AADT0 2023
Car
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track Trailer
Total
869
149
1189
68
24
7
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rate
(2015-2025)
Growth
rate
(2026-2047)
AADT0 at 2028
9.72
9.72
9.31
9.31
9.31
9.99
9.99
9.99
10.11
8.81
8.81
8.68
8.68
8.68
8.99
8.99
8.99
9.1
2150 370
169
60
17
109
35
19
13
2939
Table 7- 56: Base year Traffic (at 2028) - AADT1 – Station 2 (Road segment 3)
AADT0 2023
Growth
Car
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track Trailer
Total
869
149
68
24
7
22
7
4
3
1154
9.72
9.72
9.31
9.31
9.31
9.99
9.99
9.99
10.11
8.81
8.81
8.68
8.68
8.68
8.99
8.99
8.99
9.1
2150 370
169
60
17
54
18
9
6
rate
(2015-2025)
Growth
rate
(2026-2047)
AADT0 at 2028
2852
Table 7- 57: Base year Traffic (at 2028) - AADT1 – Station 2 (Road segment 1-1)
AADT0 2023
Growth
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track Trailer
Total
997
198
84
30
7
32
13
9
3
1373
9.72
9.72
9.31
9.31
9.31
9.99
9.99
9.99
10.11
8.81
8.81
8.68
8.68
8.68
8.99
8.99
8.99
9.1
2465 491
207
74
18
78
32
21
7
rate
(2015-2025)
Growth
Car
rate
(2026-2047)
AADT0 at 2028
3393
Table 7- 58: Base year Traffic (at 2028) - AADT1 – Station 2 (Road segment 1-2)
Car
AADT0 2023
Growth
(2015-2025)
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track Trailer
1304 224
103
36
10
33
11
6
4
9.72
9.31
9.31
9.31
9.99
9.99
9.99
10.11
rate
9.72
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AADT0 at 2028
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Car
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track Trailer
8.81
8.81
8.68
8.68
8.68
8.99
8.99
8.99
9.1
3224 554
253
89
25
81
26
14
9
Total
4278
Table 7- 59: Base year Traffic (at 2028) - AADT1 – Station 3 Road segment 5
AADT0 2023
Growth
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track Trailer
Total
272
75
36
21
7
20
21
0
0
452
9.72
9.72
9.31
9.31
9.31
9.99
9.99
9.99
10.11
8.81
8.81
8.68
8.68
8.68
8.99
8.99
8.99
9.1
673
185
88
53
18
49
51
0
0
rate
(2015-2025)
Growth
Car
rate
(2026-2047)
AADT0 at 2028
1117
Table 7- 60: Base year Traffic (at 2028) - AADT1 – Station 4 (Road segment 4,8 & 9)
AADT0 2023
Growth
4WD S/Bus M/Bus L/Bus S/Truck M/Truck H/Truck Track Trailer
Total
255
98
31
12
1
19
11
10
0
438
9.72
9.72
9.31
9.31
9.31
9.99
9.99
9.99
10.11
8.81
8.81
8.68
8.68
8.68
8.99
8.99
8.99
9.1
631
242
77
30
2
48
28
24
0
rate
(2015-2025)
Growth
Car
rate
(2026-2047)
AADT0 at 2028
7.4.7.2.2 Traffic forecast in the Design Period
Traffic projection has been made for 20 consecutive years of the design period from the opening of
the road to traffic by applying the growth rates estimated above. The following gives the forecasted
traffic for each year of the design period of the project. The projection is made for normal, diverted
and generated traffic only. For the development induced traffic, constant traffic volume given above
is summed to the other traffic at each year of the design period since the induced volume of traffic is
computed from the full capacity of the agricultural product and sugar factories.
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Table 7- 61: Traffic forecast of road segment 6 and 7 at station 1 for the years 2028– 2047
Road segment 6 and 7
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus S/Truck
M/Truck H/Truck Track Trailer
Total Sum
2028
670
131
8
7
1
14
8
7
0
845
2029
729
142
9
7
1
16
9
7
0
920
2030
793
155
10
8
1
17
10
8
0
1001
2031
863
168
10
8
1
19
11
9
0
1089
2032
939
183
11
9
1
20
12
9
0
1185
2033
1,022
199
12
10
1
22
13
10
0
1290
2034
1,112
217
13
11
1
24
14
11
0
1403
2035
1,210
236
14
12
1
26
15
12
0
1527
2036
1,316
257
16
13
2
29
17
13
0
1662
2037
1,432
279
17
14
2
31
18
14
0
1808
2038
1,559
304
19
15
2
34
20
16
0
1968
2039
1,696
331
20
16
2
37
22
17
0
2141
2040
1,845
360
22
18
2
40
23
19
0
2330
2041
2,008
392
24
19
2
44
26
20
0
2535
2042
2,185
426
26
21
3
48
28
22
0
2759
2043
2,377
464
28
23
3
52
30
24
0
3002
2044
2,587
505
31
25
3
57
33
26
0
3266
2045
2,815
549
33
27
3
62
36
29
0
3554
2046
3,063
598
36
29
4
68
39
31
0
3867
2047
3,332
650
39
32
4
74
43
34
0
4208
Year
Goods Vehicles
Source; consultant
Table 7- 62: Traffic forecast of road segment 2 at station 2 for the years 2028– 2047
Road segment 2 and 10
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus
S/Truck M/Truck
H/Truck Track Trailer
Total Sum
2028 2150
370
169
60
17
109
35
19
13
2939
2029 2,339
402
183
65
18
118
38
21
14
3198
2030 2,545
438
199
70
20
129
42
22
15
3480
2031 2,769
476
216
77
22
141
46
25
16
3787
2032 3,013
518
235
83
24
153
50
27
18
4120
Year
Goods Vehicles
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Road segment 2 and 10
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus
S/Truck M/Truck
H/Truck Track Trailer
Total Sum
2033 3,279
564
256
90
26
167
54
29
19
4483
2034 3,568
613
278
98
28
182
59
32
21
4878
2035 3,882
667
302
107
30
198
64
35
23
5308
2036 4,224
726
328
116
33
216
70
38
25
5776
2037 4,596
790
356
126
36
236
76
41
28
6285
2038 5,001
860
387
137
39
257
83
45
30
6839
2039 5,441
935
421
149
42
280
91
49
33
7441
2040 5,921
1,018
458
162
46
305
99
53
36
8097
2041 6,442
1,108
497
176
50
332
108
58
39
8810
2042 7,010
1,205
540
191
54
362
118
63
43
9586
2043 7,628
1,311
587
208
59
395
128
69
46
10431
2044 8,300
1,427
638
226
64
430
140
75
51
11350
2045 9,031
1,552
694
245
69
469
152
82
55
12350
2046 9,826
1,689
754
267
75
511
166
89
60
13438
2047 10,692
1,838
819
290
82
557
181
97
66
14622
Year
Goods Vehicles
Source; consultant
Table 7- 63: Traffic forecast of road segment 3 at station 2 for the years 2028– 2047
Road segment 3
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus
S/Truck M/Truck
H/Truck Track Trailer
Total Sum
2028 2150
370
169
60
17
54
18
9
6
2852
2029 2,339
402
183
65
18
59
19
10
7
3103
2030 2,545
438
199
70
20
64
21
11
7
3376
2031 2,769
476
216
77
22
70
23
12
8
3673
2032 3,013
518
235
83
24
77
25
13
9
3997
2033 3,279
564
256
90
26
83
27
15
10
4349
2034 3,568
613
278
98
28
91
30
16
11
4731
2035 3,882
667
302
107
30
99
32
17
12
5148
2036 4,224
726
328
116
33
108
35
19
13
5601
2037 4,596
790
356
126
36
118
38
21
14
6095
2038 5,001
860
387
137
39
128
42
22
15
6631
2039 5,441
935
421
149
42
140
45
24
16
7215
Year
Goods Vehicles
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Road segment 3
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus
S/Truck M/Truck
H/Truck Track Trailer
Total Sum
2040 5,921
1,018
458
162
46
152
49
27
18
7850
2041 6,442
1,108
497
176
50
166
54
29
20
8541
2042 7,010
1,205
540
191
54
181
59
32
21
9294
2043 7,628
1,311
587
208
59
197
64
34
23
10112
2044 8,300
1,427
638
226
64
215
70
38
25
11002
2045 9,031
1,552
694
245
69
234
76
41
28
11971
2046 9,826
1,689
754
267
75
256
83
45
30
13025
2047 10,692
1,838
819
290
82
279
90
49
33
14172
Year
Goods Vehicles
Source; consultant
Table 7- 64: Traffic forecast of road segment 1-1 at station 2 for the years 2028– 2047
Road segment 1-1
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus
S/Truck M/Truck
H/Truck Track Trailer
Total Sum
2028 2465
491
207
74
18
78
32
21
7
3393
2029 2,682
534
225
81
19
85
35
23
7
3692
2030 2,919
581
245
88
21
93
38
25
8
4017
2031 3,176
632
266
96
23
101
41
28
8
4371
2032 3,456
688
289
104
25
111
45
30
9
4756
2033 3,760
748
314
113
27
120
49
33
10
5174
2034 4,091
814
341
123
29
131
53
36
11
5630
2035 4,452
886
371
133
32
143
58
39
12
6126
2036 4,844
964
403
145
35
156
63
42
13
6665
2037 5,271
1,049
438
157
38
170
69
46
14
7252
2038 5,735
1,141
476
171
41
185
75
50
16
7891
2039 6,241
1,242
517
186
45
202
82
55
17
8586
2040 6,790
1,351
562
202
48
220
89
60
19
9342
2041 7,389
1,470
611
220
53
240
97
65
20
10164
2042 8,039
1,600
664
239
57
261
106
71
22
11060
2043 8,748
1,741
722
259
62
285
116
78
24
12034
2044 9,518
1,894
784
282
68
310
126
85
26
13093
2045 10,357
2,061
852
306
74
338
137
92
29
14246
2046 11,269
2,242
926
333
80
369
150
100
31
15501
Year
Goods Vehicles
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Road segment 1-1
Year
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus
S/Truck M/Truck
H/Truck Track Trailer
Total Sum
2,440
1,007
87
402
109
16866
2047 12,262
362
Goods Vehicles
163
34
Source; consultant
Table 7- 65: Traffic forecast of road segment 1-2 at station 2 for the years 2028– 2047
Road segment 1-2
Private Vehicles
Public Transport
Car
4WD
S/Bus M/Bus
L/Bus
S/Truck M/Truck
H/Truck Track Trailer
Total Sum
2028 3224
554
253
89
25
81
26
14
9
4278
2029 3,508
603
275
97
27
89
29
15
10
4654
2030 3,818
656
299
106
30
97
31
17
11
5064
2031 4,154
714
324
115
32
105
34
18
12
5510
2032 4,520
777
353
125
35
115
37
20
13
5995
2033 4,918
845
383
136
38
125
41
22
15
6523
2034 5,351
920
417
147
42
136
44
24
16
7097
2035 5,823
1,001
453
160
45
149
48
26
17
7722
2036 6,336
1,089
492
174
49
162
53
28
19
8402
2037 6,894
1,185
535
189
53
177
57
31
21
9142
2038 7,501
1,290
581
206
58
193
62
34
23
9947
2039 8,162
1,403
632
223
63
210
68
37
25
10822
2040 8,881
1,527
686
243
69
229
74
40
27
11775
2041 9,664
1,661
746
264
75
249
81
43
29
12812
2042 10,515
1,808
811
287
81
272
88
47
32
13940
2043 11,441
1,967
881
312
88
296
96
52
35
15168
2044 12,449
2,140
958
339
96
323
105
56
38
16503
2045 13,546
2,329
1,041
368
104
352
114
61
41
17956
2046 14,739
2,534
1,131
400
113
383
124
67
45
19537
2047 16,038
2,757
1,229
435
123
418
136
73
49
21258
Year
Goods Vehicles
Source; consultant
Table 7- 66: Traffic forecast of road segment 5 at station 3 for the years 2028– 2047
Road segment 5
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Private Vehicles
Public Transport
Car
4WD
S/Bus
M/Bus
L/Bus
S/Truck
M/Truck
H/Truck
2028
673
185
88
53
18
49
51
2029
732
202
95
57
20
54
2030
796
219
103
62
22
2031
867
239
112
68
2032
943
260
122
2033
1,026
283
2034
1,116
2035
Year
Goods Vehicles
Track
Total
Trailer
Sum
0
0
1117
56
0
0
1215
58
61
0
0
1322
23
64
67
0
0
1439
73
25
69
73
0
0
1565
133
80
28
76
79
0
0
1703
307
144
87
30
82
86
0
0
1853
1,215
335
157
94
33
90
94
0
0
2017
2036
1,322
364
170
102
35
98
102
0
0
2194
2037
1,438
396
185
111
39
107
112
0
0
2387
2038
1,565
431
201
121
42
116
122
0
0
2598
2039
1,703
469
219
132
46
127
132
0
0
2827
2040
1,853
510
238
143
49
138
144
0
0
3076
2041
2,016
555
258
155
54
150
157
0
0
3346
2042
2,194
604
281
169
58
164
172
0
0
3641
2043
2,387
657
305
184
64
179
187
0
0
3962
2044
2,597
715
332
199
69
195
204
0
0
4311
2045
2,826
778
360
217
75
212
222
0
0
4691
2046
3,075
847
392
236
82
231
242
0
0
5104
2047
3,346
921
426
256
89
252
264
0
0
5553
Source; consultant
Table 7- 67: Traffic forecast of road segment 4, 8 and 9 at station 4 for the years 2028– 2047
Road segment 4,8 and 9 forecast @ station-4
Private
Vehicles
Public Transport
Car
4WD
S/Bus
M/Bus
L/Bus
S/Truck
M/Truck H/Truck
2028
631
242
77
30
2
48
28
2029
687
263
84
32
2
52
2030
748
286
91
35
2
2031
813
312
99
38
2032
885
339
107
41
Year
Goods Vehicles
Track
Total
Trailer
Sum
24
0
1083
31
26
1
1178
57
34
28
1
1282
3
62
37
31
1
1395
3
68
40
33
1
1518
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Road segment 4,8 and 9 forecast @ station-4
Private
Vehicles
Public Transport
Car
4WD
S/Bus
M/Bus
L/Bus
S/Truck
M/Truck H/Truck
2033
963
369
117
45
3
74
44
2034
1,048
402
127
49
3
81
2035
1,140
437
138
53
4
2036
1,241
475
150
58
2037
1,350
517
163
2038
1,469
563
2039
1,598
2040
Year
Goods Vehicles
Track
Total
Trailer
Sum
36
1
1651
48
40
1
1797
88
52
43
1
1955
4
96
56
47
1
2128
63
4
104
62
51
1
2315
177
68
5
114
67
56
1
2519
612
192
74
5
124
73
61
1
2741
1,739
666
209
80
5
135
80
67
1
2983
2041
1,892
725
227
87
6
147
87
73
1
3246
2042
2,059
789
247
95
6
161
95
79
2
3532
2043
2,240
859
268
103
7
175
103
86
2
3843
2044
2,438
934
292
112
8
191
112
94
2
4182
2045
2,653
1,016
317
122
8
208
123
102
2
4551
2046
2,886
1,106
345
132
9
227
134
112
2
4952
2047
3,140
1,203
374
144
10
247
146
122
2
5389
Source; consultant
Design Standard
The design standard of a road is determined by the volume of traffic on the project road at the mid of
the design period. The following table shows the design standard of the road sections with respect to
mid-year traffic volume.
Table 7- 68: Design Standard for sections of the Project Road
Station
Project road segments
Mid-Year (2033) AADT
Design Standard Remark
1
Road segment 6 and 7
1968
DC6
ERA 2013
Road segment 2and 10
6839
DC7
ERA 2013
Road segment 3
6631
DC7
ERA 2013
Road segment 1-1
7891
DC7
ERA 2013
Road segment 1-2
9947
DC7
ERA 2013
3
Road segment 5
2598
DC6
ERA 2014
4
Road segment 4,8 and 9
2519
DC 6
ERA 2013
2
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The design standard estimation for each station is as shown in the above, the road segments fall on
to DC6 and DC7 as per the projected traffic at midyear.
7.4.8
Traffic Loading
Axle load survey
Axle load survey on the project road could not be conducted because of presence of few commercial
vehicles at the time of survey, which will give inaccurate data. Instead, equivalency factor from the
nearby and similar nature project has been collected and used for the project.
Mean Equivalency Factor (EF)
The Consultant has not carried out axle load survey specific for this project. It has rather adopted
from other studies carried out for similar projects, and from nearby project. Literatures recommend
that equivalency factor is better defined if the equivalency factor is collected from surveys conducted
countrywide, preferably from similar projects. The following tables’ gives average EF used for similar
projects
Equivalency Factor / Truck Factor from similar Project
Damage to a road pavement is not purely a function of the amount of traffic but rather the wheel or
axle loading from the traffic. Light cars and vans have little effect on a pavement whilst heavily
loaded trucks have a major impact.
The vehicle damage factor is a multiplier for converting the number of commercial vehicles of
different axle loads to the number of standard axle load repetitions. Design of the pavement
structure is based upon the cumulative number of 8.16 tone equivalent standard axles (ESA) that will
pass over the road during the design period.
Equivalency factors as recommended by ERA Pavement Design Manual have been used to convert
the axle load spectrum into an equivalent number of standard axles. It has been ascertained that the
damaging effect of axles on flexible pavement is approximately proportional to the 4.5th power of the
axle load as its computed using Liddle’s formula.
The truck and equivalence factor are determined using the following relation,
 AL ( kg ) 
EF  

 8160 
4 .5
Liddle Equation……...8.1
n
TF   EF
i 1
Equation …………….8.2
Where, EF = Equivalence Factor,
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AL = measured Axle Load,
TF = Truck Factor,
n = the number of axles of the vehicle.
For this study, the consultant has used axle load measurements carried for the road project AACRA
package 37 Lot-1 Road project near of the project area. Table 3-67 below summarizing truck factors
adapted from the aforementioned road project report.
Table 7- 69: Equivalency Factors, ESA/Vehicle Type
Vehicle type
Truck Factor
S. Bus
0.10
M/Bus
0.30
L/Bus
1.70
ST
0.30
MT
1.30
HT
7.70
TT
14.10
Equivalency
factor
adopted
from
AACRA package 37 Lot-1 Road
project report.
Source: AACRA package 37 Lot-1 Road project report
Using the volume of each class of traffic given above, and the Equivalency Factors given in Table 76 enables to determine a Cumulative Number of Equivalent Axles for each section of the project.
Design Traffic in terms of cumulative number of ESA (CESA)
Based on the cumulative traffic volume for each class of vehicles in one direction over the design
period and the corresponding equivalency factors, the cumulative number of equivalent standard
axles over the design period is determined using the formula given below. The design period for the
analysis is 20 years from the year 2023.
CESA EF*(0.5* AADT1 *365*((1 i)n 1) / i)
The analysis for the determination of the cumulative number of ESAs is presented in the tables
below.
Engineering Works Consultant PLC.
150
Consultancy Services for Topographic Survey, Drainage Facility Study,
Detailed Engineering Design, Tender Document Preparation and
Economic Evaluation of Chiro Town Internal Asphalt Road Design Project.
Oromia Roads and Logistics Bureau
Draft Engineering Design Report
July 2023
Table 7- 70: CESA for Road segment 6 and Road segment 7 at Station 1
Road segment 6 and Road segment 7 ESAL Estimation
Private Vehicles
Public Transport
Cars
Year
and
4Two
Three
Mini
Taxi
WD Wheeler wheeler Bus
Midi Bus
2028 0
0
0
0
146.95
357.79
2029 0
0
0
0
159.71
388.85
2030 0
0
0
0
173.57
422.60
2031 0
0
0
0
188.63
459.28
2032 0
0
0
0
205.01
499.15
2033 0
0
0
0
222.80
542.47
2034 0
0
0
0
242.14
589.56
2035 0
0
0
0
263.16
640.73
2036 0
0
0
0
286.00
696.35
2037 0
0
0
0
310.83
756.79
2038 0
0
0
0
337.81
822.48
2039 0
0
0
0
367.13
893.87
2040 0
0
0
0
399.00
971.46
2041 0
0
0
0
433.63
1055.78
2042 0
0
0
0
471.27
1147.42
2043 0
0
0
0
512.17
1247.02
2044 0
0
0
0
556.63
1355.26
2045 0
0
0
0
604.95
1472.90
2046 0
0
0
0
657.46
1600.75
2047 0
0
0
0
714.52
1739.69
Engineering Works Consultant PLC.
ESA
Std.
Bus
250.65
272.40
296.05
321.75
349.67
380.03
413.01
448.86
487.82
530.17
576.18
626.20
680.55
739.62
803.82
873.59
949.42
1031.83
1121.39
1218.73
LGV
788.05
858.90
936.12
1020.27
1111.99
1211.96
1320.92
1439.67
1569.09
1710.16
1863.90
2031.46
2214.09
2413.14
2630.08
2866.52
3124.23
3405.09
3711.21
4044.85
Medium
Truck
1980.24
2158.27
2352.29
2563.76
2794.25
3045.45
3319.24
3617.64
3942.86
4297.32
4683.65
5104.71
5563.63
6063.80
6608.93
7203.08
7850.63
8556.40
9325.63
10164.00
Heavy
Truck
9340.17
10179.85
11095.01
12092.46
13179.57
14364.41
15655.77
17063.23
18597.21
20269.10
22091.29
24077.30
26241.85
28600.99
31172.22
33974.60
37028.92
40357.82
43985.99
47940.33
151
Truck
trailer
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
12863.85
14017.97
15275.64
16646.16
18139.64
19767.13
21540.64
23473.28
25579.34
27874.36
30375.32
33100.67
36070.57
39306.96
42833.75
46676.99
50865.09
55428.99
60402.42
65822.12
Cumulative
number of
ESA
Traffic
Class
Cumulative
number of
ESA
Traffic
class
12863.85
26881.82
42157.46
58803.62
76943.26
96710.38
118251.02
141724.31
167303.64
195178.01
225553.32
258654.00
294724.57
334031.53
376865.28
423542.27
474407.36
529836.35
590238.77
656060.89
LV2
LV2
LV2
LV2
LV2
LV2
T1/LV3
T1/LV3
T1/LV3
T1/LV3
T1/LV3
T1/LV3
T1/LV3
T2/LV4
T2/LV4
T2/LV4
T2/LV4
T2/LV5
T2/LV5
T2/LV5
656,061
T2/V5
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Detailed Engineering Design, Tender Document Preparation and
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Oromia Roads and Logistics Bureau
Draft Engineering Design Report
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Table 7- 71: CESA for Road segment 2 and 10 at Station 2
Road segment 2 and 10 ESAL Estimation
Private Vehicles
Cars
Year
and
4Two
Three
Taxi WD Wheeler wheeler
2028 0
0
0
0
2029 0
0
0
0
2030 0
0
0
0
2031 0
0
0
0
2032 0
0
0
0
2033 0
0
0
0
2034 0
0
0
0
2035 0
0
0
0
2036 0
0
0
0
2037 0
0
0
0
2038 0
0
0
0
2039 0
0
0
0
2040 0
0
0
0
2041 0
0
0
0
2042 0
0
0
0
2043 0
0
0
0
2044 0
0
0
0
2045 0
0
0
0
2046 0
0
0
0
2047 0
0
0
0
Public Transport
Mini Bus
3075.53
3342.49
3632.62
3947.93
4290.61
4663.03
5067.78
5507.67
5985.73
6505.29
7069.95
7683.63
8350.56
9075.39
9863.14
10719.26
11649.69
12660.88
13759.85
14954.20
Midi Bus
3264.77
3548.15
3856.13
4190.84
4554.60
4949.94
5379.60
5846.55
6354.03
6905.56
7504.96
8156.39
8864.37
9633.79
10470.01
11378.80
12366.48
13439.89
14606.48
15874.32
Engineering Works Consultant PLC.
Std. Bus
5228.56
5682.40
6175.63
6711.67
7294.25
7927.39
8615.48
9363.31
10176.04
11059.32
12019.27
13062.55
14196.38
15428.62
16767.82
18223.27
19805.05
21524.13
23392.43
25422.89
LGV
5941.74
6475.91
7058.09
7692.61
8384.18
9137.92
9959.41
10854.77
11830.61
12894.18
14053.37
15316.77
16693.74
18194.51
19830.20
21612.93
23555.93
25673.61
27981.67
30497.22
Medium
Truck
8354.03
9105.06
9923.61
10815.74
11788.07
12847.82
14002.84
15261.69
16633.72
18129.09
19758.90
21535.22
23471.24
25581.30
27881.06
30387.57
33119.41
36096.85
39341.96
42878.80
Heavy
Truck
26606.06
28997.94
31604.86
34446.14
37542.84
40917.95
44596.47
48605.69
52975.34
57737.83
62928.46
68585.72
74751.58
81471.75
88796.06
96778.82
105479.24
114961.82
125296.89
136561.08
152
Truck
trailer
32372.56
35318.46
38532.44
42038.89
45864.43
50038.10
54591.56
59559.40
64979.30
70892.42
77343.63
84381.90
92060.65
100438.17
109578.04
119549.64
130428.66
142297.67
155246.76
169374.21
ESA
84843.25
92470.41
100783.37
109843.82
119718.99
130482.14
142213.15
154999.07
168934.78
184123.69
200678.54
218722.17
238388.52
259823.54
283186.33
308650.31
336404.48
366654.86
399626.03
435562.73
Cumulative
number of
ESA
Traffic
Class
Cumulative
number of
ESA
Traffic
class
84843.25
177313.66
278097.03
387940.85
507659.83
638141.98
780355.13
935354.20
1104288.98
1288412.67
1489091.21
1707813.39
1946201.91
2206025.45
2489211.78
2797862.08
3134266.56
3500921.42
3900547.45
4336110.18
LV2
T1/LV3
T1/LV3
T2/LV4
T2/LV5
T2/LV5
T3
T3
T3
T3
T3
T4
T4
T4
T4
T4
T5
T5
T5
T5
4,336,110
T5
Consultancy Services for Topographic Survey, Drainage Facility Study,
Detailed Engineering Design, Tender Document Preparation and
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Oromia Roads and Logistics Bureau
Draft Engineering Design Report
July 2023
Table 7- 72: CESA for Road segment 3 at Station 2
Road segment 3 ESAL Estimation
Year
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
Private Vehicles
Car
s
4Two
and W
Wheel
er
Taxi D
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Public Transport
Three
wheele
r
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Mini Bus
3075.53
3342.49
3632.62
3947.93
4290.61
4663.03
5067.78
5507.67
5985.73
6505.29
7069.95
7683.63
8350.56
9075.39
9863.14
10719.26
11649.69
12660.88
13759.85
14954.20
Midi Bus
3264.77
3548.15
3856.13
4190.84
4554.60
4949.94
5379.60
5846.55
6354.03
6905.56
7504.96
8156.39
8864.37
9633.79
10470.01
11378.80
12366.48
13439.89
14606.48
15874.32
Engineering Works Consultant PLC.
Std. Bus
5228.56
5682.40
6175.63
6711.67
7294.25
7927.39
8615.48
9363.31
10176.04
11059.32
12019.27
13062.55
14196.38
15428.62
16767.82
18223.27
19805.05
21524.13
23392.43
25422.89
LGV
2970.87
3237.95
3529.04
3846.31
4192.09
4568.96
4979.71
5427.38
5915.30
6447.09
7026.68
7658.38
8346.87
9097.26
9915.10
10806.47
11777.97
12836.81
13990.84
15248.61
Medium
Truck
4177.02
4552.53
4961.80
5407.87
5894.04
6423.91
7001.42
7630.85
8316.86
9064.55
9879.45
10767.61
11735.62
12790.65
13940.53
15193.79
16559.71
18048.42
19670.98
21439.40
Heavy
Truck
13303.03
14498.97
15802.43
17223.07
18771.42
20458.97
22298.23
24302.85
26487.67
28868.91
31464.23
34292.86
37375.79
40735.87
44398.03
48389.41
52739.62
57480.91
62648.45
68280.54
153
Truck
trailer
16186.28
17659.23
19266.22
21019.45
22932.22
25019.05
27295.78
29779.70
32489.65
35446.21
38671.81
42190.95
46030.32
50219.08
54789.02
59774.82
65214.33
71148.83
77623.38
84687.11
ESA
Cumulative
number of
ESA
Traffic
Class
Cumulative
number of
ESA
Traffi
c
class
48206.05
52521.72
57223.87
62347.13
67929.22
74011.25
80638.01
87858.30
95725.29
104296.9
113636.3
123812.3
134899.9
146980.
160143.6
174485.8
190112.8
207139.8
225692.3
245907.0
48206.05
100727.77
157951.65
220298.78
288228.00
362239.25
442877.26
530735.56
626460.85
730757.79
844394.15
968206.52
1103106.43
1250087.11
1410230.76
1584716.58
1774829.43
1981969.32
2207661.70
2453568.77
LV2
T1/LV3
T1/LV3
T2/LV3
T2/LV3
T2/LV4
T2/LV4
T2/LV5
T2/LV5
T3
T3
T3
T3
T3
T3
T4
T4
T4
T4
T4
2,453,569
T4
Consultancy Services for Topographic Survey, Drainage Facility Study,
Detailed Engineering Design, Tender Document Preparation and
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July 2023
Table 7- 73: CESA for Road segment 1-1 at Station 2
Road segment 1-1 ESAL Estimation
Private Vehicles
Cars
Year
and
4Two
Three
Taxi WD Wheeler wheeler
2028 0
0
0
0
2029 0
0
0
0
2030 0
0
0
0
2031 0
0
0
0
2032 0
0
0
0
2033 0
0
0
0
2034 0
0
0
0
2035 0
0
0
0
2036 0
0
0
0
2037 0
0
0
0
2038 0
0
0
0
2039 0
0
0
0
2040 0
0
0
0
2041 0
0
0
0
2042 0
0
0
0
2043 0
0
0
0
2044 0
0
0
0
2045 0
0
0
0
2046 0
0
0
0
2047 0
0
0
0
Public Transport
Mini Bus
3778.26
4106.21
4462.63
4849.99
5270.96
5728.48
6225.72
6766.11
7353.41
7991.68
8685.36
9439.25
10258.58
11149.02
12116.76
13168.49
14311.52
15553.76
16903.82
18371.07
Midi Bus
4073.68
4427.27
4811.56
5229.20
5683.09
6176.39
6712.50
7295.14
7928.36
8616.54
9364.46
10177.29
11060.68
12020.75
13064.15
14198.12
15430.52
16769.89
18225.51
19807.49
Engineering Works Consultant PLC.
Std. Bus
5540.13
6021.02
6543.64
7111.63
7728.92
8399.79
9128.89
9921.28
10782.44
11718.36
12735.51
13840.95
15042.35
16348.03
17767.03
19309.21
20985.25
22806.77
24786.40
26937.86
LGV
4287.96
4673.45
5093.59
5551.51
6050.59
6594.53
7187.38
7833.53
8537.76
9305.31
10141.85
11053.61
12047.32
13130.38
14310.80
15597.34
16999.54
18527.80
20193.45
22008.84
Medium
Truck
7542.03
8220.06
8959.05
9764.47
10642.29
11599.03
12641.79
13778.28
15016.95
16366.97
17838.37
19442.03
21189.87
23094.84
25171.07
27433.95
29900.26
32588.29
35517.98
38711.05
Heavy
Truck
29968.33
32662.48
35598.84
38799.17
42287.22
46088.84
50232.23
54748.10
59669.96
65034.29
70880.87
77253.06
84198.11
91767.52
100017.42
109008.99
118808.89
129489.81
141130.95
153818.62
154
Truck
trailer
16783.85
18311.19
19977.50
21795.46
23778.84
25942.72
28303.50
30879.12
33689.12
36754.83
40099.52
43748.58
47729.70
52073.10
56811.76
61981.63
67621.95
73775.55
80489.13
87813.64
ESA
71974.24
78421.67
85446.80
93101.41
101441.91
110529.78
120432.00
131221.56
142978.00
155787.98
169745.94
184954.78
201526.62
219583.64
239258.99
260697.72
284057.93
309511.87
337247.24
367468.56
Cumulative
number of
ESA
Traffic
Class
Cumulative
number of
ESA
Traffic
class
71974.24
150395.92
235842.72
328944.13
430386.05
540915.83
661347.83
792569.39
935547.39
1091335.38
1261081.32
1446036.10
1647562.71
1867146.35
2106405.34
2367103.06
2651161.00
2960672.87
3297920.10
3665388.67
LV2
T1/LV3
T1/LV3
T2/LV4
T2/LV4
T2/LV5
T2/LV5
T3
T3
T3
T3
T3
T4
T4
T4
T4
T4
T4
T5
T5
3,665,389
T5
Consultancy Services for Topographic Survey, Drainage Facility Study,
Detailed Engineering Design, Tender Document Preparation and
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Oromia Roads and Logistics Bureau
Draft Engineering Design Report
July 2023
Table 7- 74: CESA for Road segment 1-2 at Station 2
Road segment 1-2 ESAL Estimation
Year Private Vehicles
Cars
and
4Two
Three
Taxi
WD Wheeler wheeler
2028 0
0
0
0
2029 0
0
0
0
2030 0
0
0
0
2031 0
0
0
0
2032 0
0
0
0
2033 0
0
0
0
2034 0
0
0
0
2035 0
0
0
0
2036 0
0
0
0
2037 0
0
0
0
2038 0
0
0
0
2039 0
0
0
0
2040 0
0
0
0
2041 0
0
0
0
2042 0
0
0
0
2043 0
0
0
0
2044 0
0
0
0
2045 0
0
0
0
2046 0
0
0
0
2047 0
0
0
0
Public Transport
Mini Bus
4613.30
4613.30
5013.73
5448.92
5921.89
6435.91
6994.55
7601.68
8261.50
8978.60
9757.94
10604.93
11525.44
12525.85
13613.09
14794.71
16078.89
17474.54
18991.32
20639.77
Midi Bus
1632.38
4897.15
5322.22
5784.19
6286.26
6831.91
7424.92
8069.40
8769.82
9531.04
10358.34
11257.44
12234.59
13296.55
14450.69
15705.01
17068.21
18549.73
20159.84
21909.72
Engineering Works Consultant PLC.
Std. Bus
461.34
7842.84
8523.59
9263.44
10067.51
10941.37
11891.08
12923.23
14044.96
15264.07
16588.99
18028.91
19593.82
21294.56
23142.93
25151.74
27334.91
29707.58
32286.20
35088.64
LGV
1485.44
4456.31
4856.93
5293.57
5769.46
6288.13
6853.44
7469.56
8141.07
8872.96
9670.64
10540.03
11487.57
12520.31
13645.88
14872.65
16209.70
17666.95
19255.21
20986.25
Medium
Truck
481.96
6265.52
6828.80
7442.70
8111.80
8841.05
9635.87
10502.13
11446.27
12475.29
13596.82
14819.17
16151.42
17603.43
19185.98
20910.80
22790.68
24839.56
27072.64
29506.47
Heavy
Truck
259.15
19954.54
21748.46
23703.64
25834.60
28157.13
30688.46
33447.35
36454.27
39731.51
43303.37
47196.34
51439.29
56063.69
61103.81
66597.04
72584.12
79109.43
86221.37
93972.67
155
Truck
trailer
172.19
24279.42
26488.85
28899.33
31529.17
34398.32
37528.57
40943.67
44669.55
48734.48
53169.31
58007.72
63286.42
69045.49
75328.63
82183.53
89662.23
97821.50
106723.25
116435.07
ESA
9105.77
72309.08
78782.58
85835.81
93520.70
101893.83
111016.88
120957.02
131787.45
143587.94
156445.40
170454.55
185718.55
202349.87
220471.01
240215.48
261728.73
285169.28
310709.83
338538.58
Cumulative
number of
ESA
Traffic
Class
Cumulative
number of
ESA
Traffic
class
9105.77
81414.85
160197.43
246033.24
339553.93
441447.77
552464.65
673421.66
805209.11
948797.05
1105242.45
1275697.00
1461415.55
1663765.42
1884236.43
2124451.91
2386180.64
2671349.91
2982059.74
3320598.33
LV2
LV2
T1/LV3
T2/LV3
T2/LV4
T2/LV4
T2/LV5
T2/LV5
T3
T3
T3
T3
T3
T4
T4
T4
T4
T4
T4
T5
3,320,598
T5
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Table 7- 75: CESA for Road segment 5 at Station 3
Road segment 5 ESAL Estimation
Private Vehicles
Cars
Year
and
4Taxi
WD Two Wheeler
2028 0
0
0
2029 0
0
0
2030 0
0
0
2031 0
0
0
2032 0
0
0
2033 0
0
0
2034 0
0
0
2035 0
0
0
2036 0
0
0
2037 0
0
0
2038 0
0
0
2039 0
0
0
2040 0
0
0
2041 0
0
0
2042 0
0
0
2043 0
0
0
2044 0
0
0
2045 0
0
0
2046 0
0
0
2047 0
0
0
Public Transport
Three
wheeler
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Mini
Bus
1597.46
1736.12
1886.81
2050.59
2228.58
2422.02
2632.25
2860.73
3109.04
3378.91
3672.19
3990.94
4337.35
4713.84
5123.00
5567.67
6050.95
6576.17
7146.98
7767.34
Midi Bus
2883.05
3133.30
3405.27
3700.84
4022.08
4371.19
4750.61
5162.97
5611.11
6098.16
6627.48
7202.74
7827.94
8507.40
9245.85
10048.39
10920.59
11868.49
12898.68
14018.28
Engineering Works Consultant PLC.
Std. Bus
5652.93
6143.61
6676.87
7256.43
7886.28
8570.81
9314.76
10123.28
11001.98
11956.95
12994.82
14122.77
15348.62
16680.88
18128.78
19702.36
21412.53
23271.13
25291.07
27486.33
LGV
2690.57
2932.45
3196.08
3483.41
3796.57
4137.88
4509.87
4915.31
5357.20
5838.81
6363.72
6935.82
7559.35
8238.93
8979.61
9786.88
10666.72
11625.66
12670.81
13809.91
Medium
Truck
12192.91
13289.05
14483.74
15785.82
17204.97
18751.70
20437.47
22274.80
24277.31
26459.84
28838.58
31431.16
34256.83
37336.51
40693.07
44351.37
48338.56
52684.20
57420.51
62582.61
156
Heavy
Truck
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Truck
trailer
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
ESA
25016.92
27234.53
29648.77
32277.09
35138.48
38253.60
41644.97
45337.09
49356.64
53732.66
58496.78
63683.43
69330.09
75477.57
82170.31
89456.68
97389.35
106025.66
115428.04
125664.48
Cumulative
number of
ESA
Traffic
Class
Cumulative
number of
ESA
Traffic
class
25016.92
52251.44
81900.21
114177.30
149315.78
187569.38
229214.35
274551.44
323908.07
377640.74
436137.52
499820.95
569151.04
644628.61
726798.92
816255.60
913644.94
1019670.60
1135098.65
1260763.13
LV2
LV2
LV2
T1/LV3
T1/LV3
T1/LV3
T1/LV3
T1/LV3
T1/LV4
T1/LV4
T1/LV4
T1/LV4
T2/LV5
T2/LV5
T3
T3
T3
T3
T3
T3
1,260,763
T3
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Table 7- 76: CESA for Road segment 4,8 and 9 at Station 4
Road segment 4,8 and 9 ESAL Estimation
Private Vehicles
Public Transport
Cars
Year
and
4Two
Three
Mini
Midi
Taxi WD Wheeler wheeler Bus
Bus
2028 0
0
0
0
1405.45 1617.82
2029 0
0
0
0
1527.44 1758.24
2030 0
0
0
0
1660.03 1910.86
2031 0
0
0
0
1804.12 2076.72
2032 0
0
0
0
1960.71 2256.98
2033 0
0
0
0
2130.90 2452.89
2034 0
0
0
0
2315.87 2665.80
2035 0
0
0
0
2516.88 2897.19
2036 0
0
0
0
2735.35 3148.66
2037 0
0
0
0
2972.78 3421.97
2038 0
0
0
0
3230.81 3719.00
2039 0
0
0
0
3511.25 4041.80
2040 0
0
0
0
3816.02 4392.63
2041 0
0
0
0
4147.25 4773.91
2042 0
0
0
0
4507.24 5188.29
2043 0
0
0
0
4898.46 5638.63
2044 0
0
0
0
5323.65 6128.07
2045 0
0
0
0
5785.74 6659.98
2046 0
0
0
0
6287.95 7238.07
2047 0
0
0
0
6833.74 7866.33
Engineering Works Consultant PLC.
Std.
Bus
623.15
677.24
736.02
799.91
869.34
944.80
1026.81
1115.93
1212.80
1318.07
1432.48
1556.82
1691.95
1838.81
1998.42
2171.88
2360.40
2565.28
2787.95
3029.94
LGV
2634.18
2870.99
3129.09
3410.40
3716.99
4051.15
4415.35
4812.29
5244.91
5716.43
6230.34
6790.45
7400.91
8066.25
8791.40
9581.75
10443.15
11381.99
12405.23
13520.46
Medium
Truck
6730.04
7335.07
7994.49
8713.19
9496.51
10350.25
11280.73
12294.87
13400.18
14604.86
15917.83
17348.85
18908.51
20608.38
22461.08
24480.33
26681.11
29079.74
31694.01
34543.30
Heavy
Truck
33330.60
36327.02
39592.82
43152.21
47031.59
51259.73
55867.98
60890.52
66364.57
72330.75
78833.28
85920.39
93644.64
102063.29
111238.78
121239.15
132138.55
144017.80
156965.00
171076.15
157
Truck
trailer
1195.15
1303.91
1422.56
1552.02
1693.25
1847.34
2015.44
2198.85
2398.95
2617.25
2855.42
3115.26
3398.75
3708.04
4045.47
4413.61
4815.24
5253.43
5731.49
6253.06
ESA
47536.38
51799.91
56445.87
61508.56
67025.38
73037.06
79587.98
86726.53
94505.42
102982.10
112219.16
122284.82
133253.41
145205.93
158230.67
172423.81
187890.16
204743.97
223109.70
243122.99
Cumulative
number of
ESA
Traffic
Class
Cumulative
number of
ESA
Traffic
class
47536.38
99336.28
155782.15
217290.71
284316.09
357353.15
436941.13
523667.66
618173.08
721155.18
833374.34
955659.15
1088912.56
1234118.49
1392349.16
1564772.97
1752663.13
1957407.10
2180516.80
2423639.79
LV2
LV2
T2/LV3
T1/LV3
T2/LV3
T2/LV4
T2/LV4
T2/LV5
T2/LV5
T3
T3
T3
T3
T3
T3
T4
T4
T4
T4
T4
2,423,640
T4
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Design Traffic Classes
The following table gives the traffic class as obtained from the axle load survey analysis presented
above.
Table 7- 77: Design Traffic Classes
Station.
Project Road Segments
No
1
Cumulative number of
ESAs (106)
Traffic class Remark
Road segment 6 and 7
0.656
T2/LV5
As per ERA PDM, 2013
Road segment 2 and 10
4.33
T5
As per ERA PDM, 2013
Road segment 3
2.45
T4
As per ERA PDM, 2013
Road segment 1-1
3.66
T5
As per ERA PDM, 2013
Road segment 1-2
3.32
T5
As per ERA PDM, 2013
3
Road segment 5
1.26
T3
As per ERA PDM, 2013
4
Road segment 4,8 and 9
2.423
T4
As per ERA PDM, 2013
2
7.5
Subgrade Soil Investigation.
7.5.1
General
The subgrade soil investigation was aimed to assess the actual condition of the alignment soil which
includes soil extension survey, sampling, logging and testing.
The purposes of the sub grade soil investigation along the road corridor are:

To assess the nature of the material along the road alignment,

To characterize physical and mechanical properties of material along the route alignment.

To identify problematic soils and to suggest possible remedial measures that would suit
the pavement design.
The detailed sub grade field investigation along the road corridor is presented in the following sub
section.
7.5.2
Soil Extension Survey
The soil extension survey along the road corridor is carried out by visual observation of the color,
texture, moisture and appearance of the soil along the road side and from test pits log.
Accordingly, the dominant road bed material of Chiro Town Road Segments Are Dark brown silty
CLAY soil which is commonly Poor roadbed material. The Graphical representation of soil extension
survey presented here in figure below but detail soil extension survey along the road alignment is
presented in Annex of this report.
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Table 7- 78: Summary of the roadbed materials
Length
Subgrade
Subgrade soil type
(km)
Extension composition
dark brown to brown , silty CLAY soil
10.665
48%
Grey Slightly to Moderately weathered Rock
underlying Fresh basaltic rock
poor/Unsuitable
Good subgrade
5.30
24%
Grey highly weathered to decomposed
rock
soil Remark
Fair to poor
,
silty CLAY soil with gravel
4.013
18%
light grey to Dark Brown SILTY CLAY soil
2.224
10%
Fair to poor
Figure 7- 1: Summary of Soil Extension
7.5.3
Sampling and Logging
To determine the engineering properties and to assess the suitability of the soils along the road
alignment, representative disturbed samples were collected by digging test pits along the road
alignment. Test pits of approx. 1.0 m x 1.0 m size at staggered position are excavated up to 1.2m
depth below the original surface of the road at regular intervals of 0.5km, and the lithological soil
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formations were properly logged. After collecting the samples, the sample tags are labeled and
inserted into sample bags with the following information:

The project name;

GPS/Station of sampling;

Depth of sampling;

Type of material sampled and;

The type of test required
After completing the logging and sampling, the test pits were backfilled, compacted and leveled off to
their original level.
The test pit logs are summarized and presented in Annex–II of this soil and material report.
7.5.4
Subgrade Soil Analysis.
The subgrade soil was investigated by visual observation, pit excavation and sampling of
representative soil layers from the test pits.
As mentioned above, samples of sub-grade materials were collected from the road alignment at
every 0.5km interval to assess the properties of the road bed materials. Classification tests (sieve
analysis, atterberg limits, and natural moisture content) were conducted on samples collected at
interval of 0.5Km, while modified proctor, three point CBR and swell tests were conducted at interval
of 0.5Km in staggered manner. The test results are summarized and presented in Appendix.
For easy analysis and understanding nearby routes are categorized as follow;
1. Muze tera to TTC road segment
2. Kebet tera to Chiro wereda office and Sumeya bridge to Addis ketema Road segments
3. Agape Hotel to Agri research Center to TTC Road segment and
Agri research Center to ODA Bultu university to Main Asphalt Road
4. Chiro Town Administration to mticho to Leila Road Segment
5. Hundi gudina Scl to Nejebac Kidan mihiret Road Segment and Hundi gudina Scl to Aschalew
Hotel Road Segments
6. Blood Bank to Genda to Quteba Bono Road Segments
7. Chiro wereda office to Care Ethiopia Road Segment
Almost all group of roads traverses dark brown silty CLAY soil (expansive soil), which is characterize
as poor/unsuitable sub grade material except chiro town administration to mudhicho No.9 School,
which dominates fair to good subgrade materials, detail material test result presented in Annex IV.
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Plasticity Analysis
An indication as to the nature of the soil along the route may be given by the variation in Liquid
Limit(LL) and Plasticity Index (PI). LL&PI is influenced by the type and proportion of clay minerals
present within the material and high LL&PI values are often an indication of expansiveness of the
soil.
The variation of PI and LL along the project road Segments are presented in figure 4.1 below. It can
be seen from the figure that the values of PI range from NP to 41%, and Liquid limit value range from
NP to 75%. Liquid limit < or =60% is 69% and PI < or =30% is 78% is calculated from laboratory test
result for all Road segments excavated pit.
Figure 7- 2: Variation of Plastic Index (PI) for the Road project
The plasticity of a soil can also be expressed in terms of the plasticity chart shown below. The
plasticity chart helps to classify the type of soils based on their plasticity characteristics (i.e.
Atterberg Limits and Index of soils). Generally, materials falling above the A-Line are classified as
clays and below the A-Line are as silts. As can be noted from the graphs below road alignment,
majority of soils along the road alignment fall under the group CL and ML&OL can be described as
Low plastic silty soil and low plastic clay. The plasticity chart of sub grade soil for the all sections are
presented in the Figure below
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CH
MH&OH
CL
ML & CL
ML & OL
Figure 7- 3: Plasticity Chart for all project Road Segments Sub-grade soil
Sub grade Soil Classification
AASHTO soil classification reveals that the sub grade materials along all Road Segments section of
the alignments mainly classified as A-1-b, A-2-7, A-4, A-6, A-7-5 and A-7-6 soil groups. Out of the
Six Groups A-7-6 comprise 35.3% of the sub grade material (the largest proportion) which is
followed by A-7-5, 33.3% then A-2-7,25.5% and A-1-b, A-4 and A-6 materials which constituent 2 %,
2% and 2% of the sub grade soil, respectively. Composition of the sub grade soil materials for the
road alignment is summarized in the figure 4.3 below.
Figure 7- 4: Percentage compositions of sub-grade soil for all Road Segments of the Project.
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Sub Grade Strength Analysis
7.5.4.3.1 Maximum Dry Density (MDD) AND Optimum Moisture Content (OMC)
Soil samples obtained from test pits have been compacted in the laboratory at various moisture
contents to derive a dry density versus moisture content relationship. Compaction tests were carried
out at 0.5km intervals, in accordance with AASHTO T180 (4.5 kg hammer or heavy hammer). The
MDD value along the alignment ranges between 1.340 g/cm3 and 2.25g/cm3 The Maximum Dry
Density (MDD) obtained from these tests is summarized in Figure 4.3 for all road segments of the
project.
Figure 7- 5: Variation of MDD along All road segments.
The optimum Moisture Content (OMC) along the road alignment varies from 11% to 29%. The
values of Optimum Moisture Content (OMC) obtained from the compaction tests are presented in
Figure 4.4 below.
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Figure 7- 6: Variation of OMC along All road segments
7.5.4.3.2 California Bearing Ratio (CBR) and Swell Values
Soaked CBR tests were carried out on disturbed soil samples recovered from trial pits along the road
segments alignment to determine the shear strength of the sub-grade material. Three-point CBRs
were undertaken in accordance to AASHTO T-193 to determine the variation of sub grade strength
with increasing compaction effort. The CBR value at 93% of MDD is plotted in Figure 4.6 below.
Figure 7- 7: CBR Value for all Road segments of the Project
As can be seen from the above figures, the CBR values @ 93% of MDD along all road segments
alignment vary between 0.8% and 50.5%. 33% of the CBR value is greater than or equal to 5% and
the remaining 67% of the CBR values is less than 5%. This implies that most sections of the road
segments alignment of the project has a subgrade class of S1, as per ERA sub grade classification.
The swell value of the samples is also determined along with the CBR test to evaluate the potential
heaving of the sub grade soils. Accordingly, the CBR swell value vary between 0.2% and 12.2%.
37% of the sub grade soil CBR swell value is less than 3% and the rest of 63% of the CBR swell of
the sub grade soil is greater than 3%.
Hence, according to the CBR test result as well as the CBR swell value most of the Road segments
alignment of the project are very weak and are having high heaving potential. The variation of CBRSwell value for all road segments of the project are presented in the figures below
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Figure 7- 8: Variation of CBR-swell value for all Road segments of the Project
7.5.5
Subgrade Soil Data Interpretation
Analysis and interpretation of sub grade soil
As mentioned above; 47 samples of sub-grade materials were collected from the road segments
alignment at every 0.5km interval to assess the properties and strength of the road bed materials.
Classification tests (sieve analysis and atterberg limits and modified proctor, three point CBR and
swell tests were conducted on samples collected at every 0.5km. The test results are summarized
and presented in Annex III
The classification test result reveals that the sub-grade materials along the road segments are
classified into Six different groups A-1-b, A-2-7, A-4, A-6, A-7-5 and A-7-6 Out of the six groups A-76 comprise 35.3% of the subgrade material (the largest proportion) which is followed by A-7-5 &A-27 materials which constituent 33.3%,25.5 respectively. The remaining groups of soil classification
comprise total 6% of the subgrade. The sub grade material rating according to AASHTO and Project
test result rating comprise the samples for critical parameters with the stretch they represent
summarized with the following tables.
Table 7- 79: Analysis and interpretation of sub grade soil
Material
Percent
LL
rating <=60
PI
Swell
Group
<=30
CBR > <= 3 index
Rating
classificat compositi
AASHTO
ion
on(%)
(M145)
(%)
(%)
=5 (%)
(%)
range
Test result
A-7-6
34
Fair to Poor
94
88
13
25
1-35
poor to fair
A-7-5
31.9
Fair to Poor
33
47
7
7
8-43
Poor subgrade`
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Material
Percent
LL
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PI
Swell
<=30
CBR > <= 3 index
Rating
(%)
(%)
=5 (%)
(%)
range
Test result
77
92
85
85
0-3
rating <=60
Group
classificat compositi
AASHTO
ion
on(%)
(M145)
A-2-7
27.7
A-6
2.1
Fair to Poor
100
100
100
100
6
poor to fair
A-4
2.1
Fair to Poor
100
100
0
0
2
Poor subgrade
A-1-b
2.1
Excellent to Good
100
100
100
100
0
poor to fair
Excellent to Good
from
Fair
to
Good/excellent
Table 7- 80: Comparison of project rating with AASHTO rating
Material
Project rating
AASHTO Rating
Comparison
classific
with
ation
AASHTO
Reason for the difference (if there is any)
Rating
A-7-6
Fair to Poor
Fair to Poor
A-7-5
Poor subgrade
Fair
A-2-7
A-6
poor to fair
A-4
poor to fair
According
to
ERA
subgrade
test
to The same
-
Good
AASHTO
According to ERA design manual table 3.3
Rate
typical design CBR values , their LL & PI
project Rate
According
Fair to Poor
Excellent
A-1-b
project Rate
Requirement of LL,PI,CBR-SWELL &CBR
Fair to Poor
Poor subgrade
-
Fair to Poor
to Excellent
Good/excellent
The same
to
ERA
subgrade
test
Requirement of LL,PI,CBR-SWELL &CBR
to project Rate
According to AASHTO LL specification
Good
The liquid limit values and plasticity index value shows that the majority of the samples are low
plasticity. But CBR & CBR-Swell Value shows that majority of the soil samples are weak and high
expansive subgrade respectively, which confirms that majority of the subgrade soils have low
plasticity and Weak expansive behavior.
7.5.6
Unsuitable soil sections
The natural sub-grade soils along the existing road stretches of the proposed roads is characterized
by Dark brown CLAY SILTY soil, which are relatively high in swell value and weak in bearing
capacity. These stretches have been identified by using the criteria set in the ERA Standard
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Specification, 2013, section 4103. Accordingly, sections where LL is less than 60%, Pl less than 30%
and swell > 3.0% and the sub grade strengths is weak (CBR<3%) are identified as given in table
below.
Table 7- 81: Unsuitable soil stretches for all Road segments of the Project
Limits for
Sr.
New Station Interval
No
From
To
LL
PI
Swell
CBR
Degree of
Expansion
Km
degree of
expansion Remark
**
LL
PI
Chiro Town Administration to Mtichu to Lelia
1
0+000 0+700 0.7
55
23
5
2
Medium
>60
2
1+500 2+100 0.6
55
29
9.4
1.4
Medium
>60
3
2+100 3+000 0.9
63
34
0.9
14.9
high
to
Very high
>60
25-
Due to PI,
41
swell
25-
Due to Swell
41
&CBR
25-
Due to LL,
41
PI
Muze tera to TTC to Qilisa road segment
0+450 0+700 0.25
62
31
10.3
1
high
>60
2
0+700 1+300 0.6
48
24
5
4
high
>60
3
1+300 1+700 0.4
51
24
4
3
Medium
>60
4
2+400 3+200 0.8
54
23
5.6
2.1
Medium
>60
5
3+200 3+700 0.5
57
28
6.3
2.2
high
>60
6
4+100 6+047 1.947
58-
25-
2.2-
63
32
4.9
2.8-8 high
>60
28
Due to LL,
PI
,Swell
&CBR
25-
Due to Swell
41
&CBR
25-
Due to LL,
41
swell& CBR
25-
Due to LL,
41
swell& CBR
25-
Due to LL,
41
swell& CBR
25-
Due to LL,
41
swell& CBR
Hundi gudina School to Nejubac Kidest kidan mihiret Church road segment
1
0+000 2+536 2.536
54-
23-
7.1-
1.08-
72
38
10.8
2.2
Engineering Works Consultant PLC.
Very high
>60
2541
Due to LL,
PI,
CBR
167
swell&
Expansive(Unsuitable section)
1
15-
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Limits for
Sr.
New Station Interval
No
From
To
LL
PI
Swell
CBR
Degree of
Expansion
Km
degree of
expansion Remark
**
LL
PI
Agricultural research center to Oda Bultu Universtity to Main Asphalt road road segment
1
2
3
0+000 0+400 0.4
0+400 1+000 0.6
1+000 1+236 0.236
62-
29-
6-
1.4-
high
75
41
11.4
2.42
Very high
62-
29-
6-
1.4-
75
41
11.4
2.42
62
28
9
1
to
Very high
Very high
>60
>60
>60
2541
2541
2541
Due to LL,
PI,
swell& CBR
Due to LL,
PI,
swell& CBR
Due to LL,
PI,
swell& CBR
Hundi gudina School to Aschalew Hotel road segment
1
0+000 0+855 0.855
54-
28-
3.4-
1.4-
64
31
10.8
3.22
Very high
>60
2541
Due to LL,
PI,
swell& CBR
Blood bank to Genda to Quteba Bono road segment
1
2
3
4
5
0+000 1+022 1.022
0+000 0+153 0.153
52
56
0+000 0+141 0+141 45
0+000 0+214 0.214
0+000 0+096 0.096
52
56
24
25
21
24
25
7
6
2
7
6
Engineering Works Consultant PLC.
1
3
4
1
3
medium
medium
medium
medium
medium
>60
>60
>60
>60
>60
2541
2541
2541
2541
2541
Due to LL,
PI,
swell& CBR
Due to LL,
PI,
swell& CBR
Due to LL,
PI,
swell& CBR
Due to LL,
PI,
swell& CBR
Due to LL,
PI,
swell& CBR
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Limits for
Sr.
New Station Interval
No
From
To
LL
PI
Swell
CBR
Degree of
Expansion
Km
degree of
expansion Remark
**
LL
PI
Sumeya bridge to Addis ketema Road segment
1
0+000 0+524 0.524
67
36-
8.8-
1.1-
37
9.4
1.4
Very high
>60
2541
Due to LL,
PI,
swell& CBR
Agape Hotel to Agricultural research center to TTC Road segment
1
0+000 0+584 0.584
54-
28-
60
30
11
1.11.4
Very high
>60
2541
Due to LL,
PI,
swell& CBR
Chiro wereda office to Care Ethiopia Road Segment
1
0+000 1+647 1.647
54-
23-
8.5-
0.8-
63
28
14.6
1.9
medium
>60
25-
Due to LL,
41
swell& CBR
Therefore, this sections need to be treated and appropriate construction method shall be applied
during construction
7.6
Pavement Design
In the design of the pavement, the sub-grade design CBR values and Traffic classes obtained as
discussed above will be used. The design is carried out by using ERA’s Flexible Pavement design
manual (2013).
7.6.1
Pavement Design Using ERA’s Pavement Design Manual.
According to the homogenous sub grade soil, the road segments are divided into Five sections. The
five sections are from (km 0+000 to km 3+500, km 3+500 to km 6+208.54), (km 0+000 to km 3+500,
km 3+500 to km 6+047.38), (Km 0+000 to Km 2+765.67, km 0+000 to km 0+855 km, km 0+000 to
km 1+235.88, km 0+000 to km 1+235.88, 0+000 to km 1+040.14, 0+000 to km 0+518.98, km 0+000
to km 0+580 Km) with a design CBR value of 2 %, 14 %,2%,2% and 1% which are classified as S1,
S4, S1, S1 and S1 sub grade classes, respectively, before treatment. However, after unsuitable
sections are treated with better materials the sub grade class is improved to S4, S5, S3, S3 and S3,
for the homogenous sections from (km 0+000 to km 3+500, km 3+500 to km 6+208.54), (km 0+000
to km 3+500, km 3+500 to km 6+047.38), (Km 0+000 to Km 2+765.67, km 0+000 to km 0+855 km,
km 0+000 to km 1+235.88, km 0+000 to km 1+235.88, 0+000 to km 1+040.14, 0+000 to km
0+518.98, km 0+000 to km 0+580 Km, km 0+000 to km 1+647), respectively as per ERA flexible
pavement design manual 2013.
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The design CBR and the sub grade class before and after the treatment of the in-situ sub grade are
given in the table below.
Table 7- 82: Design CBR and sub grade class before and after treatment
90 percentile
Homogeneous section
CBR
Value
before
Sub
grade
Class before
treatment
treatment
90 percentile 90 percentile
CBR
Value CBR
Value
after
after
treatment
treatment
I. Chiro town Adminstration to Mticho to Leila Road Segments Homogenous Section Determination
Section I1 (Km 0+000– Km 3+500)
2%
S1
8
S4
Section I2 (Km 3+500 – Km6+208.54)
14 %
S4
19
S5
II. Muzi Tera to TTC to Qilisa Road Segments Homogenous Section Determination
Section II3 (Km 0+000– Km 3+500)
2%
S1
5
S3
Section II4 (Km 3+500 – Km6+047.38)
2%
S1
5
S3
III.1 Hundi gudina School to Nejubas kidest Kidanmihiret Church
Km 0+000 to Km 2+765.67
1%
S1
5
S3
III.2 kebet tera to Chiro woreda office and Chiro wereda office to Care Ethiopia
km 0+000 to km 1+235.88 and km
0+000 to km 1+647
1%
S1
5
S3
S1
5
S3
III.3 Agricultural research center to Oda Bultu University
km 0+000 to km 1+235.88
1%
III,Hundi gudina School to Aschalew hotel, , , Blood bank to Genda to Quteba bono, to Sumeya bridge
to Addis ketema and Agape hotel to Agri research center to TTC Road SegmentsDesign CBR of
Homogenous Sections.
Section III5 (, km 0+000 to km 0+855
km, 0+000 to km 1+040.14, 0+000 to 1%
S1
5
S3
km 0+518.98, km 0+000 to km 0+580)
According to the sub grade and traffic class presented for the sections of the road Segments, the
pavement design of the road varies with the traffic class T5, T4, T3 and T2/LV5 as table 4-6 above.
Whereas the sub grade class are S3, S4 and S5 for the different sections of the road. The table here
under presents the sub grade and traffic class as determined above.
Table 7- 83: summery of sub grade and traffic class for the section of the road Segments.
90
Homogeneous section
CBR
percentile 90
percentile Traffic class
Value CBR Value after
after treatment
treatment
I. Chiro town Adminstration to Mticho to Leila Road Segments Homogenous Section Determination
Engineering Works Consultant PLC.
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90
Homogeneous section
CBR
Oromia Roads and Logistics Bureau
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percentile 90
percentile Traffic class
Value CBR Value after
after treatment
treatment
Section I1 (Km 0+000– Km 3+500)
8
S4
T2/LV5
Section I2 (Km 3+500 – Km6+208.54)
19
S5
T2/LV5
II. Muzi Tera to TTC to Qilisa Road Segments Homogenous Section Determination
Section II3 (Km 0+000– Km 3+500)
5
S3
T5
Section II4 (Km 3+500 – Km6+047.38)
5
S3
T5
III.1 Hundi gudina School to Nejubas kidest Kidanmihiret Church
Km 0+000 to Km 2+765.67
5
S3
T2/LV5
III.2 kebet tera to Chiro woreda office and Chiro wereda office to Care Ethiopia
km 0+000 to km 1+235.88 and km 0+000 to km
1+647
5
S3
T5
S3
T3
III.3 Agricultural research center to Oda Bultu University
km 0+000 to km 1+235.88
5
III,Hundi gudina School to Aschalew hotel, Blood bank to Genda to Quteba bono, to Sumeya bridge to
Addis ketema and Agape hotel to Agri research center to TTC Road SegmentsDesign CBR of
Homogenous Sections.
Section III5 (, km 0+000 to km 0+855 km, 0+000
to km 1+040.14, 0+000 to km 0+518.98, km 5
S3
T4
0+000 to km 0+580)
The ESAL for the road segments of Chiro town administration to Mitcho to leila is 0.656 Million. Even
though 0.656 million ESAL is at the border of T3 traffic class, and manuals recommend to take the
next traffic class in such cases. The above table indicates the combination of the homogenous sub
grade class with that of the Traffic class as studied by the consultant
Hence, the road Segments are designed using ERA Flexible Pavement Design Manual, 2013, Chart
B1 with thin (50mm) Flexible AC Surfacing, Granular Road Base to meet the desired pavement
surfacing thickness to withstand the traffic load in the design period. The thicknesses as adopted
from the charts is presented in the tables below.
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Table 7- 84: Pavement thickness as per ERA 2013 Flexible Pavement Design Manual Chart B1
Pavement Layer Thickness (mm)
Sub grade
Traffic
Station
Design
Sub Sub
grade
CBR grade
at 93% MDD
class
Surfac
Sub
Improv
course
base
ed sub
ing AC CBR >1 CBR > grade
(mm)
class
Base
00%
30%
CBR >
(mm)
(mm)
15%
Remark
I. Chiro town Adminstration to Mticho to Leila Road Segments Homogenous Section Determination
Section I1 (Km 0+000–
Km 3+500)
ERA PDM,
8
S4
T3
50
175
150
-
2013,
Chart B1
Section I2 (Km 3+500
– Km6+208.54)
ERA PDM,
19
S5
T3
50
150
100
-
2013,
Chart B1
II. Muzi Tera to TTC to Qilisa Road Segments Homogenous Section Determination
Section
II3
(Km
0+000– Km 3+500)
ERA PDM,
5
S3
T5
50
175
325
-
2013,
Chart B1
Section II4 (Km 3+500
– Km6+047.38)
ERA PDM,
5
S3
T5
50
175
325
-
2013,
Chart B1
III.1 Hundi gudina School to Nejubas kidest Kidanmihiret Church
Km
0+000
to
Km
2+765.67
ERA PDM,
5
S3
T3
50
175
225
-
2013,
Chart B1
III.2 kebet tera to Chiro woreda office and Chiro wereda office to Care Ethiopia
km
0+000
1+235.88
to
and
km
ERA PDM,
km 5
S3
T5
50
175
325
-
0+000 to km 1+647
2013,
Chart B1
III.3 Agricultural research center to Oda Bultu University
km
0+000
to
1+235.88
km
ERA PDM,
5
S3
T3
50
175
225
-
2013,
Chart B1
III,Hundi gudina School to Aschalew hotel, Blood bank to Genda to Quteba bono, to Sumeya bridge to Addis
ketema and Agape hotel to Agri research center to TTC Road SegmentsDesign CBR of Homogenous Sections.
Section
III5
(,
km 5
S3
T4
Engineering Works Consultant PLC.
50
175
275
-
172
ERA PDM,
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Pavement Layer Thickness (mm)
Sub grade
Traffic
Station
Design
Sub Sub
grade
CBR grade
at 93% MDD
Oromia Roads and Logistics Bureau
Draft Engineering Design Report
July 2023
class
Surfac
Sub
Improv
course
base
ed sub
Remark
ing AC CBR >1 CBR > grade
(mm)
class
Base
00%
30%
CBR >
(mm)
(mm)
15%
0+000 to km 0+855
2013,
km,
Chart B1
0+000
1+040.14,
km
to
km
0+000
to
0+518.98,
km
0+000 to km 0+580)
* According to ERA 2013 pavement design manual, up to 100mm of sub base may be substituted
with selected fill provided the sub base is not reduced to less than the road base thickness or
200mm whichever is greater. The substitution ratio of sub base to selected fill is 1 to 1.3.
Hence, with improved sub grade (capping) material, the layer thickness can be as given in the table
below.
Table 7- 85: Pavement thickness as per ERA 2013 Flexible Pavement Design Manual Chart B1
Pavement Layer Thickness (mm)
Sub grade
Traffic
Station
Design
Sub Sub
grade
CBR grade
at 93% MDD
class
Surfac
Sub
Improv
course
base
ed sub
ing AC CBR >1 CBR > grade
(mm)
class
Base
00%
30%
CBR >
(mm)
(mm)
15%
Remark
I. Chiro town Adminstration to Mticho to Leila Road Segments Homogenous Section Determination
Section I1 (Km 0+000–
Km 3+500)
8
S4
T3
50
175
150
-
ERA
PDM,
2013,
Chart
B1
Section I2 (Km 3+500
– Km6+208.54)
19
S5
T3
50
150
100
-
ERA
PDM,
2013,
Chart
B1
II. Muzi Tera to TTC to Qilisa Road Segments Homogenous Section Determination
Section
II3
(Km
0+000– Km 3+500)
5
S3
T5
50
175
200
150
ERA
PDM,
2013,
Chart
B1
Section II4 (Km 3+500 5
S3
T5
Engineering Works Consultant PLC.
50
175
200
150
173
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PDM,
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Pavement Layer Thickness (mm)
Sub grade
Traffic
Station
Design
Sub Sub
grade
CBR grade
at 93% MDD
Oromia Roads and Logistics Bureau
Draft Engineering Design Report
July 2023
class
Surfac
Sub
Improv
course
base
ed sub
ing AC CBR >1 CBR > grade
(mm)
class
Base
00%
30%
CBR >
(mm)
(mm)
15%
– Km6+047.38)
Remark
2013,
Chart
B1
III.1 Hundi gudina School to Nejubas kidest Kidanmihiret Church
Km
0+000
to
Km
2+765.67
5
S3
T3
50
175
150
100
ERA
PDM,
2013,
Chart
B1
III.2 kebet tera to Chiro woreda office and Chiro wereda office to Care Ethiopia
km
0+000
to
1+235.88
and
km
km 5
S3
T5
50
175
200
150
0+000 to km 1+647
ERA
PDM,
2013,
Chart
B1
III.3 Agricultural research center to Oda Bultu University
km
0+000
to
km
1+235.88
5
S3
T3
50
175
150
100
ERA
PDM,
2013,
Chart
B1
III,Hundi gudina School to Aschalew hotel, Blood bank to Genda to Quteba bono, to Sumeya bridge to Addis
ketema and Agape hotel to Agri research center to TTC Road SegmentsDesign CBR of Homogenous Sections.
Section
km
ERA
PDM,
0+000 to km 0+855
2013,
Chart
km,
III5
0+000
1+040.14,
km
(,
to
km
0+000
to
0+518.98,
5
S3
T4
50
175
200
100
B1
km
0+000 to km 0+580)
7.6.2
Design of Shoulder
Shoulder is designed to provide lateral support for the pavement layers, and help in removal of
surface water from the road surface and facilitates internal drainage of the pavement. Shoulders also
give additional width for emergency and temporary parking.
According to ERA Flexible Pavement Design Manual 2013; for a paved road it is usually
economically justifiable to provide paved rather than unpaved shoulders. This is because it greatly
improves pavement performance by ensuring that the zone of seasonal moisture variation does not
penetrate to the outer wheel track and it:
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i)....Reduces erosion of the shoulders (especially on steep gradients).
ii)... Reduces maintenance costs by avoiding the need for re-gravelling at regular intervals.
iii).. Reduces the risk of road accidents, especially where the edge drops between the shoulder
and the pavement is significant or the shoulders are relatively soft (since the gravel surface
wears out leading to edge drop, and becomes irregular and accumulates water to soften the
pavement layers).
In order to achieve the above objectives shoulder shall at least be sealed by Double Bituminous
Surface Treatment (DBST), and sealed to a width of at least 1.0 from the edge of the sealed running
surface. However, provision is often required for non-motorized traffic of various kinds and shoulder
widths are variable (see ERA’s Geometric Design Manual), hence, the width of the sealed shoulder
is also variable. Paved or sealed shoulders should be differentiated from the carriageway e.g. by the
use of edge markings to avoid regular use of traffic.
Moisture is the most important factor that affects pavement performance and long-term maintenance
costs. Thus one of the significant challenges faced by the designers is to provide a pavement
structure in which the detrimental effects of moisture are contained to acceptable limits. This
situation therefore places extra emphasis on drainage and moisture control for achieving satisfactory
pavement life. In this respect, two inter-related aspects of drainage need to be considered during
road design: internal and external drainages.
External drainage can be achieved by providing a carriageway and shoulder slopes which can help
the shedding of water into the side drains. A suitable value for paved roads is about 2.5% to 3% for
the carriageway, and 4-6% for the shoulders. On the other hand, internal drainage concerns about
water that entered the road structure directly from above the road pavement or directly from below
the pavement structures. Drainage within the pavement layers is an essential element of structural
design since it is impossible to guarantee that road surfaces will remain waterproof throughout their
lives. Shoulder design should therefore ensure that water is able to drain out quickly from within the
pavement. This can be achieved by extending the pervious layers provided under the carriageway to
the outer edge of the shoulder so that it can drain the engrossed water to the side ditch. Thus, the
sub base and base course layers shall extend to the outer edge of the shoulder.
Accordingly, the designed road shall have a shoulder thickness as indicated in the table below
Table 7- 86: Shoulder Pavement thickness
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Pavement Layer Thickness (mm)
Sub grade
Traffic
Station
Design
Sub Sub
grade
CBR grade
at 93% MDD
Oromia Roads and Logistics Bureau
Draft Engineering Design Report
July 2023
class
Surfac
Sub
Improv
course
base
ed sub
ing AC CBR >1 CBR > grade
(mm)
class
Base
00%
30%
CBR >
(mm)
(mm)
15%
Remark
I. Chiro town Adminstration to Mticho to Leila Road Segments Homogenous Section Determination
Section I1 (Km 0+000–
Km 3+500)
ERA PDM,
8
S4
T3
DBST
175
150
-
2013,
Chart B1
Section I2 (Km 3+500
– Km6+208.54)
ERA PDM,
19
S5
T3
DBST
150
100
-
2013,
Chart B1
II. Muzi Tera to TTC to Qilisa Road Segments Homogenous Section Determination
Section
II3
(Km
0+000– Km 3+500)
ERA PDM,
5
S3
T5
DBST
175
200
150
2013,
Chart B1
Section II4 (Km 3+500
– Km6+047.38)
ERA PDM,
5
S3
T5
DBST
175
200
150
2013,
Chart B1
III.1 Hundi gudina School to Nejubas kidest Kidanmihiret Church
Km
0+000
to
Km
2+765.67
ERA PDM,
5
S3
T3
DBST
175
150
100
2013,
Chart B1
III.2 kebet tera to Chiro woreda office and Chiro wereda office to Care Ethiopia
km
0+000
1+235.88
to
and
km
ERA PDM,
km 5
S3
T5
DBST
175
200
150
0+000 to km 1+647
2013,
Chart B1
III.3 Agricultural research center to Oda Bultu University
km
0+000
to
km
1+235.88
ERA PDM,
5
S3
T3
DBST
175
150
100
2013,
Chart B1
III,Hundi gudina School to Aschalew hotel, Blood bank to Genda to Quteba bono, to Sumeya bridge to Addis
ketema and Agape hotel to Agri research center to TTC Road SegmentsDesign CBR of Homogenous Sections.
Section
III5
(,
km
0+000 to km 0+855
5
S3
T4
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DBST
175
200
100
176
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Pavement Layer Thickness (mm)
Sub grade
Traffic
Station
Design
Sub Sub
grade
CBR grade
at 93% MDD
km,
0+000
1+040.14,
km
to
km
0+000
to
0+518.98,
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class
class
Surfac
Base
Sub
Improv
course
base
ed sub
ing AC CBR >1 CBR > grade
(mm)
00%
30%
CBR >
(mm)
(mm)
15%
Remark
Chart B1
km
0+000 to km 0+580)
* For ease of construction the shoulder at mountainous and escarpment sections should be AC
surfacing.
7.7
Design for Geo-Hazards
Geo-hazards can pose significant constraints to the construction and operation of road infrastructure,
and are therefore critically important and should be considered in the design of roads. In Ethiopia,
geology and tectonic setting, combined with climate and hydrology, create conditions that encourage
the occurrence of a range of geo-hazards. These occur naturally and are often also triggered or
exacerbated by road construction. These hazards can be grouped in to slope instability, seismic risk,
presence of poor/weak or expansive and erodible soil and presence of water logged or swampy
areas. All these geotechnical aspects investigated along the project road segments are discussed in
the following sections.
7.7.1
Weak Subgrade Soil Sections
The natural sub-grade soils of the project road segments are dominantly Dark brown to brown CLAY
Soil. The road segments alignment with such unsuitable soil shall be removed and replaced with
good material or shall be treated or modified. In addition, proper side and cross drainage shall be
provided in order to avoid the risk of moisture fluctuation. The road sections with sub grade of weak
and expansive nature are shown below along with corresponding degree of expansiveness.
In order to access the unsuitableness of soils, attention has to be given to those sections where LL
is > 60, PI is > 30%, CBR swell is > 3.0% and CBR is < 3%, as stated in the ERA Standard
Technical Specification and Method of Measurement for Road Works 2013, section 4103 (a).
Accordingly, sections where PI >30 %, LL>60%, CBR<3% and CBR swell > 3.0% are identified, as
given in Table 5.1 below.
Table 7- 87: Weak and/or Expansive subgrade stretches in the road segments of the project
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Limits
Sr.
New Station Interval
No
From
To
LL
PI
Swell
CBR
for
of Remark
Degree of degree
Expansion expansion **
Km
LL
PI
Chiro Town Administration to Mtichu to Lelia
1
0+000 0+700 0.7
55
23
5
2
Medium
>60
25-41
2
1+500 2+100 0.6
55
29
9.4
1.4
Medium
>60
25-41
3
2+100 3+000 0.9
63
34
0.9
14.9
>60
25-41
high
to
Very high
Due to PI, swell
Due
to
Swell
&CBR
Due to LL, PI
Muze tera to TTC to Qilisa road segment
Due
1
0+450 0+700 0.25
62
31
10.3
1
high
>60
15-28
to
PI
LL,
,Swell
&CBR
0+700 1+300 0.6
48
24
5
4
high
>60
25-41
3
1+300 1+700 0.4
51
24
4
3
Medium
>60
25-41
4
2+400 3+200 0.8
54
23
5.6
2.1
Medium
>60
25-41
5
3+200 3+700 0.5
57
28
6.3
2.2
high
>60
25-41
6
4+100 6+047 1.947
58-
25-
2.2-
63
32
4.9
2.8-8 high
>60
25-41
Due
to
Swell
to
LL,
&CBR
Due
swell& CBR
Due
to
LL,
swell& CBR
Due
to
LL,
swell& CBR
Due
to
LL,
swell& CBR
Hundi gudina School to Nejubac Kidest kidan mihiret Church road segment
1
0+000 2+536 2.536
54-
23-
7.1-
1.08-
72
38
10.8
2.2
Very high
>60
25-41
Due to LL, PI,
swell& CBR
Agricultural research center to Oda Bultu Universtity to Main Asphalt road road segment
1
0+000 0+400 0.4
62-
29-
6-
1.4-
high
75
41
11.4
2.42
Very high
Engineering Works Consultant PLC.
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>60
25-41
Due to LL, PI,
swell& CBR
178
Expansive(Unsuitable section)
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Limits
Sr.
New Station Interval
No
From
To
LL
PI
Swell
CBR
of Remark
Degree of degree
Expansion expansion **
Km
2
0+400 1+000 0.6
3
1+000 1+236 0.236
62-
29-
6-
1.4-
75
41
11.4
2.42
62
28
9
1
for
LL
PI
Very high
>60
25-41
Very high
>60
25-41
Very high
>60
25-41
Due to LL, PI,
swell& CBR
Due to LL, PI,
swell& CBR
Hundi gudina School to Aschalew Hotel road segment
1
0+000 0+855 0.855
54-
28-
3.4-
1.4-
64
31
10.8
3.22
Due to LL, PI,
swell& CBR
Blood bank to Genda to Quteba Bono road segment
1
0+000 1+022 1.022
52
24
7
1
medium
>60
25-41
2
0+000 0+153 0.153
56
25
6
3
medium
>60
25-41
3
0+000 0+141 0+141 45
21
2
4
medium
>60
25-41
4
0+000 0+214 0.214
52
24
7
1
medium
>60
25-41
5
0+000 0+096 0.096
56
25
6
3
medium
>60
25-41
Very high
>60
25-41
Very high
>60
25-41
medium
>60
25-41
Due to LL, PI,
swell& CBR
Due to LL, PI,
swell& CBR
Due to LL, PI,
swell& CBR
Due to LL, PI,
swell& CBR
Due to LL, PI,
swell& CBR
Sumeya bridge to Addis ketema Road segment
1
0+000 0+524 0.524
67
36-
8.8-
1.1-
37
9.4
1.4
Due to LL, PI,
swell& CBR
Agape Hotel to Agricultural research center to TTC Road segment
1
0+000 0+584 0.584
54-
28-
60
30
11
1.11.4
Due to LL, PI,
swell& CBR
Chiro wereda office to Care Ethiopia Road Segment
1
0+000 1+647 1.647
54-
23-
8.5-
0.8-
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Limits
Sr.
New Station Interval
No
From
To
LL
PI
Swell
CBR
of Remark
Degree of degree
Expansion expansion **
Km
LL
63
28
14.6
for
PI
1.9
swell& CBR
**LL limits and PI limits for low, medium and high degree of expansion are as per figure 7.8 and
Table 7.1, respectively, of ERA Site Investigation manual, 2013.
7.7.2
Treatment of Weak subgrade and/or expansive clay soils
From the above table it can be seen that there are expansive and/or weak sub grade soils along
Chiro Town Internal Asphalt road project (km 0+000 to km 6+208.54, km 0+000 to km 6+047.38, Km
0+000 to Km 2+765.67, km 0+000 to km 0+855 km, km 0+000 to km 1+235.88, km 0+000 to km
1+235.88, 0+000 to km 1+040.14, 0+000 to km 0+518.98, km 0+000 to km 0+580). Therefore,
attention shall be given to those expansive and weak sub grade soil sections to improve their
bearing capacities and soil consistency to avoid the detrimental effect to the pavement layers.
There are expansive clay soil sections observed on the road segments of the project, and the test
results confirmed the same. Therefore, the following treatment measures can be employed to
mitigate its detrimental effect to the pavement layers. The proposed treatment methods are as per
provisions of ERA Site Investigation Manual, 2013, ERA Flexible Pavement Design Manual, 2013
and ERA Low Volume Roads Manual 2011.The treatment methods is irrespective of the degree of
expansion of the in-situ sub grade soil.
7.7.3
a)
Treatment method for weak subgrade sections:
Provide a minimum earth work cover of 1000mm with non-expansive material with
minimum CBR value for the sub grade class determined for the respective homogeneous
sections of the road.
b)
If the fill above the natural ground is less than 1000mm, the in-situ material shall be cut to a
depth of 1000-x, where x is the fill above the natural ground.
7.7.4
Treatment method for expansive clay soil sections:
This method shall be provided as per the design manuals mentioned above, as follows:
a) Where the finished road level is designed to be less than 2m above ground level, remove the
problem soil to a minimum depth of 600mm over the full width of the road, but ensure a
minimum earth work cover of 1000mm below the pavement layers;
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b) Where the finished road level is designed to be greater than 2m above ground level, remove
the problem soil to a depth of 600mm below the ground level under the unsurfaced area of
the road;
c) Where the expansive soil does not exceed 1m in depth, remove it to its full depth.
d) Stockpile the excavated material on either side of the excavation for subsequent spreading
on the fill slopes.
e) The excavated area shall be backfilled with a non-expansive material of CBR value greater or
equal to the minimum CBR value for the sub grade class for the respective homogeneous
sections of the road, and compacted to a density of 95% modified AASHTO.
f)
After the excavated material has been replaced with non-expansive material in 200mm lifts to
95% modified AASHTO density, the road shall be brought to finished level in approved
materials, with a side slope of 1:2 or as indicated on the Drawing. All other requirements for
pavement layers shall be complied with as specified.
g) The previously stockpiled expansive soil should then be spread over the slope (side fill) so as
to produce as flat a slope as possible (1V:6H or 1V:4H depending on the fill height)).
h) Provision of side drain should be avoided unless absolutely necessary. Where it is necessary,
it should be as shallow as possible and as far from the toe of the embankment as possible,
as indicated in the typical drawings.
7.7.5
Erodible Soil Sections
There are road side and center gully erosion sections along the designed road segments of the
project (Tab 5.2). This is due to the presence of erodible soil and unprotected surface flow causing
deep gullies along the existing road, where some of the project road segments alignment also
designed to pass through it. The presence of gully erosion along the sides of the alignment identified
should be taken as an indication that the whole topographic unit in which it is occurring may be
susceptible to erosion. The stretches and recommendation are provided in the tables below.
Table 7- 88: Existing gully locations along the proposed road
7.7.6
Treatment method for erodible soils
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The following treatment methods can be employed at where soils are susceptible to erosion
1. If gullies are already formed, they need to be backfilled layer by layer with borrow materials.
2. The side drains (longitudinal ditches) in these section shall be lined irrespective of the
longitudinal slope.
3. Turn outs shall be constructed in short possible intervals to avoid concentrated flow of water.
Secondary ditches and check dams shall be constructed to dissipate the energy of storm
water running parallel to the road.
4. Proper protection works shall be constructed at culvert inlets and outlets and at approaches.
7.7.7
Swampy or Water Logged Sections
During site reconnaissance visit and site investigation time the team try to identify this
Swampy/water logged problematic section but not find it along the road segments of the project.
7.7.8
Treatment of Swampy Sections
The following treatment measures can be employed to mitigate the detrimental effect of water to the
pavement layers.

The sub grade shall be raised to a minimum fill height of 2 meters above the natural sub
grade.

The bottom 600 mm fill shall be constructed with rock fill which consists of boulders and
gravels and the embankment above the rock fill shall be constructed by a selected material
with a minimum CBR of the sub grade class for the respective sections of the road segments,
and the fill shall be constructed in such a way that relatively coarser materials are placed on
top of the rock fill and selected materials on the top of the courser materials.

The top layer of the rock fill should not reach an elevation 600 mm below the finished sub
grade. In no case shall the sub grade layer be less than 400 mm above the top of the rock fill.
7.8
Construction Material Investigation.
7.8.1
General
Detailed investigation of material sources plays an important role in assisting the design of cost
effective pavements by enhancing efficient use of the locally available construction materials. The
construction materials investigation undertaken for the design of the road involved searching for and
identification of suitable borrow pits and quarries which could provide an adequate quality and
quantity of road construction materials within the vicinity of the road project.
After identifying the potential material sources representative samples were taken for laboratory
testing to establish the quality and suitability of the locally available road construction materials.
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Estimates of quantity was carried out for rock, gravel and borrow materials. This is done with the aid
of hand held GPS to record the coordinate of the boundaries of the suitable materials. Area of the
material is then calculated from the coordinates and the depth of usable material is measured from
the test pits, and the quantity estimated from the area and the depth of the usable material. The
depth of overburden material is also estimated and evaluated if the suitable material can be
exploited economically.
The potential sources of construction materials in the vicinity of the project area was investigated
through the following activities:
Interaction with local people and relevant bureau: Local people in the vicinity of the

route and relevant bureau such as rural road authorities were enquired about the
existence of potential sources of construction material.
Field survey for potential sources: All potential sources were visually inspected and

evaluated. Samples were taken where the material was considered suitable for the
intended purpose.
Laboratory tests were conducted on material samples: This was carried out to

assess the material quality and compare the results with the required materials
specifications.
In general, prior to locating each kind of construction materials the following factors were considered:

Performance of the materials which were used for the construction the existing road;

Accessibility;

Quantity and Quality;

Type and thickness of overburden materials;

Availability of adequate space for erecting crusher and stockpiling; and

Environmental and social aspects
Taking into account these factors Six (6) potential sources of construction materials were located,
which include possible sources of rock, natural gravel sources, and water. Moreover, representative
samples were collected from those sources for further investigation of their quality in the laboratory.
7.8.2
Rock Sources for Surfacing, Base, Concrete and Masonry Works
During the field investigation, the quality and quantity of rocks, accessibility of the quarry locations,
the overburden material depth and the suitability of the material for construction purposes are well
assessed. Besides, the environmental and social impacts which may arise following the utilization of
the rock quarry like displacement of local residents, claim for farm lands are assessed.
Possible rock sources for aggregate for asphalt concrete, base course, concrete and masonry works
are available within reasonable hauling distance. The quantity of available material has also been
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estimated. Ease of mining and development of quarry faces and suitability to erect a crusher plant
have been considered as additional factors.
Two (2) quarry sites and one masonry stone source are Sampled from 3 quarry and one masonary
identified source along the road project which is considered as suitable by visual inspection which
can likely be sources of base course, asphalt concrete, surfacing, concrete aggregates and masonry
stone. From both source representative samples are collected to be tested at central laboratory to
confirm their suitability for the intended purposes.
The formation and characteristics of the rock sources along the road corridor is fresh to slightly
weathered Basaltic formation for Aggregate quality test and Ignimbrite rock type for Masonry.
Representative sample has been taken from the identified sources for further laboratory testing.
Table 7- 89: Locations of Quary Materials Identified along the Road Segments
Offset
Sn
Statio
No
n (Km)
1
1+800
1.4km
offset
2
5+713
0.1kmOffset
RHS
3
2+300
4
0+700
Offset
from
road segment
LHS
Coordinates
Muzi tera - E=707556
TTC - Qilisa
N=1004148
Muzi tera TTC - Qilisa
Chiro
town
0.1Km offset,
Administration
RHS&LHS
– Mtichu-Leila
Kebt tera –
0.05km offset
Chiro Wereda
LHS
Office
E=707361
N=1001434
E=702894
N=1005055
E=705480
N=1003320
Engineering Works Consultant PLC.
Co
de
Q1
Q2
Description
Source
Test
Required
slightly
AC/Base
Weathered
course
basaltic rock
AC/Base
basaltic rock
course
Quantity
(Existin
g/New)
plenty
New
Limited
Existing
Q3
basaltic rock
AC/Base
course
plenty
new
Q4
slightly
Weathered
rock
Masonry
Limited
Existing
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Figure 7- 9: crushed aggregate(Crusher site) and Quarry site for Base course at station 5+818 offset 0.15km
RHS and 1+8 offset 1.2Km LHS with in vicinity of Road Segments
7.8.3
Natural Gravel for Subbase, Capping Layer and Embankment
The project road shall be constructed to the required standard that requires adequate quantity of
materials for strong lower pavement layers at reasonable intervals. Special attention is therefore
given to locating natural gravel sources that can be used for this pavement layers (i.e., sub base and
capping layers).
Grey GRAVEL SILTY with SAND & CLAY and brown weathered GRAVEL silty clay sources could
be identified at the Vicinity for all road segments. However, natural granular materials that comply
with specification requirements for their use as sub base layers without further processing are often
rare. This is mainly due to inconsistency in their grading as a result of frequent change in weathering
pattern and extreme variability of geological processes that are responsible for their present state of
occurrences.
The locations of some road segments lie with in Chiro town. Therefore, there is no construction
material along the road segments corridor and assessed around the vicinity of the town. The quality
of the materials exhibits significant variation within a source that consideration has been given to
selective production, and sampling of the materials has been carried out accordingly.
Accordingly, four (4) sources of natural gravel materials have been located and all source samples
were taken from the borrow sites within the vicinity of the road Segments.
Summary of the natural gravel sources is given in table below. The laboratory test results of natural
gravels are presented in Annex -III of this report.
Table 7- 90: Locations of Natural Gravel Materials Identified along the Road Segments
Borrow source
Sn
No
Stati
on
Offset from Coordinates
Offset
(Km)
4+90 m
0
Code
Required
Muzi tera - E=706721
Highly to moderately
TTC - Qilisa
weathered
N=1001999
offset,
B1
LHS
2
Description
segment
0.05k
1
road
1+80 1.4
Muzi tera - E=707556
0
TTC
Km
- N=1004148
B6
Engineering Works Consultant PLC.
rock
mixed with silty clay
soil.
Source
Test
Quantity
(Existing
/New)
Sub
base/Cap
plenty
Existing
ping / Fill
Moderately
Sub
Too
weathered
gravel base/Cap
plenty
185
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Borrow source
Sn
No
Stati
on
Offset from Coordinates
Offset
(Km)
road
Code
Description
Required
segment
LHS
Qilisa
Source
Test
silty clay soil
Quantity
(Existing
/New)
ping / Fill
offset
0.1Km
3
town E=702894
2+60 offset,
Administrati
0
RHS&
on – Mtichu-
LHS
Leila
0.2km
Chiro
0+82 offset
0
4
Chiro
1+26
0
N=1005055
Highly to moderately
B2
weathered
mixed
with
rock
gravel
silty clay soil
Sub
base/Cap
plenty
new
limited
Existing
plenty
new
ping / Fill
town E=704221
Administrati
LHS & on – Mtichu-
N=1005421
B4
Highly
weathered Capping /
rock silty clay soil
Fill
RHS
Leila
0.05k
Chiro
m
Administrati
offset
on – Mtichu-
RHS&
Leila
gravel silty clay soil
Blood Bank-
Highly to moderately
RHS,
Genda-
weathered
rock Sub
0.1Km
Kuteba
mixed
with base/Cap
offset
Bono
town
Highly to moderately Sub
B3
weathered
rock base/Cap
ping / Fill
LHS
5
1+24
0
B5
sandstone
new
Limited
gravel ping / Fill
silty clay soil
Figure 7- 10: 4+900 Offset 0.1Km LHS Subbase Figure 7- 11: 2+600 Offset 0.14Km LHS towards,
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existing source
7.8.4
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Sub base New source
Natural Sand Sources /Fine Aggregate
Natural sand is not available within the project area. The Chiro town communities Would have used
from mieso river sand (23km from chiro town), therefore we recommended to use this source with
crushed sand by appropriate blending
7.8.5
Water Sources for Construction
Since water is necessary for compaction, mortar and concrete works attempt was made to locate
perennial rivers and ground water locations on the Vicinity of project road Segments that can be
used as a source of water for construction. Accordingly, one (1) water source of Perennial River is
identified and representative sample was collected from the River for laboratory tests.
There is a sufficient water source for Chiro Town Internal Asphalt Road project. Sample was
collected from the river source to check the quality of the river water if it can be used for the intended
construction purposes. The water source quality tests like PH, total dissolved solids, Chloride and
Sulphate contents. The laboratory test results are attached in Annex -III.
Table 7- 91: Water source On the Vicinity of Road Segments.
Ref.
Station
No.
W1
cross
road GPS Coordinate
Chainage
segment
0+370
Muzi tera - TTC - E=705300
Qilisa
N=1005052
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Chiro river
Offset/
Type
Distance
Material
cross
road River
segments
187
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8
GEOTECHNICAL DESIGN
8.1
Geological Setting
8.1.1
Geological Setting of the Project Area
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The project is located in Western Harari Zone of Oromia Region. The project road covers
approximately 20Km and connects Chiro town governmental and community institutions of the
western hararge main Ethiopian rift. The terrain dominated with volcanic rocks that contain variable
magdala group (basalts, rhyolite & trachytic tuff, ignimbrites, rhyolite, trachyte, agglomerates,), Afar
group. Miocene-Pleistocene (Basalts, subordinate acid lavas, ignimbrites and Ashangi Groups.
Paleocene-Oligocene-Miocene (a. Alkali olivine basalts& tuffs, rare Rhyolites; b. Doleritics sills &
gabbro-diabase intrusives. in addition, the valleys and rolling terrains are covered mainly by in-situ
residual soils and some colluvium deposits which rich in clay and organic minerals. The proposed
Road segment routes are mainly volcanic rocks consist of three mapped units, which are
categorized on the basis of fissural and fault mode of volcanic activity as magadala group (upper
Miocene –Pleistocene), Ashangi Groups. Paleocene-Oligocene-Miocene (a. Alkali olivine basalts&
tuffs, rare Rhyolites; b. Doleritics sills & gabbro-diabase intrusives and Afar group. MiocenePleistocene (Basalts, subordinate acid lavas, ignimbrites.

magadala group (upper Miocene –Pleistocene): this group consist basalts, rhyolite &
trachytic tuff, ignimbrites, rhyolite, trachyte, agglomerates. It outcrops consisting of alternating
flows, ranging in thickness. It is fine to coarse grained, light to dark grey, slightly to
moderately weathered.

Ashangi Groups. Paleocene-Oligocene-Miocene (a. Alkali olivine basalts& tuffs, rare
Rhyolites; b. Dolerites sills & gabbro-diabase intrusives. It outcrops consisting of alternating
flows, ranging in thickness. It is fine to coarse grained, light to dark grey, slightly to
moderately weathered.

Afar group. Miocene-Pleistocene. Basalts, subordinate acid lavas, ignimbrites. It is
complexes which are situated along the axial zones of the Main Ethiopia Rift and Afar
Depression.it has Light grey to grey colour forming thick mass flows.
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Figure 1. 1: Geological map of the project area scale 1: 250,000 (Aman et al., 2012).
LEGEND
Pga ,NQa& NM
Ashangi Groups. Paleocene-Oligocene-Miocene, Afar group. MiocenePleistocene and Magdala group. upper Miocene –Pleistocene
8.1.2
Local Road Corridor Geological Settings
Site visit was carried out to assess the local geology, structural setting, geomorphological process
and availability of suitable materials for construction. Fieldwork is the second stage of investigation
where thoughts or facts collected & discovered during the desktop study needed to be proved or
disproved with the aid of field visual observations.
In line with this, careful site observations have been conducted in conjunction with the regional
geology of the project area to identify the local geological formations and if there exist any areas
slopes which are susceptible to instability.
Accordingly, the sections of the road project are covered mainly by Ashangi Groups. PaleoceneOligocene-Miocene (a. Alkali olivine basalts& tuffs, rare Rhyolites; b. Dolerites sills & gabbro-diabase
intrusives followed by Afar group. Miocene-Pleistocene. Basalts, subordinate acid lavas, ignimbrites
and a local geological formation is presented below.
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Photo 1. 1: slightly weathered Basaltic Rhyolite rock in the road corridor (left) and fresh Basaltic rock
(right) in the vicinity exposed
The moderately to slightly weathered Basaltic & Basaltic Rhyolite rocks can be used as sources for
fresh Aggregate &crushed sand depending on their state of weathering and fracturing. In most cases,
Dark brown to brown silty clay soils overlaid the Basaltic rock formations.
8.2
Seismic Setting and Earthquake Hazards
Seismic survey has not been carried out in the project area or in the immediate vicinity. However, a
number of seismic surveys by different local and foreign researchers (e.g. IGSSA of Addis Ababa
University, Ethiopia-Afar Geoscientific Lithospheric Experiment (EAGLE, 2001-2003), etc.) have
been carried out for several years in the Main Ethiopian Rift (MER).
As a result, earthquake epicentres are mainly located in the MER (Fig. 1.7/1.8), where tectonics and
volcanism is somewhat active. As indicated, on the seismic zone map of Ethiopia, the project road
Segments are transverses through Zones 2 and 3. In this seismic sensitive zone, it is generally the
case that extreme events of load combination, taking into account the seismic load effects, may
govern the substructure design.
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Project
Figure 1. 2: Magnitudes of earthquake in East Figure 1. 3: Seismic Hazard Zoning Map of
Africa
Ethiopia (EBCS-8)
Table 1. 8: Bedrock Acceleration Ratio
Zone
4
3
2
1
α
0.10
0.07
0.05
0.03
Therefore, it advisable to check the stability of the structure against seismic effects and appropriate
seismic design considerations shall be taken especially for main bridges into account during the
design stage by following the seismic design procedure as specified in ERA Bridge Design Manual
2013, EBCS-8, 1995 and/or AASHTO LRDF bridge design specification and other relevant
specification.
8.3
Site Reconnaissance for Slope Stability
The project road traverses through flat, rolling and mountainous terrain where light to dark brown
silty clay soils are dominantly encountered. During the site visit it is observed that most section of the
road alignment is stable with regard to slope stability related problems.
8.4
Problematic Sub-Grade Soil Sections
8.4.1
Expansive and/or Weak subgrade sections
Some section of the road alignment is exhibited expansiveness and/or weak sub grade soil nature
and which may require replacement or high fill. The table below lists Problematic/poor subgrade soil
sections.
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Table 8- 1: List of problematic subgrade sections
Sr.
No
New Station Interval
From
To
LL
PI
Swell CBR
Km
Degree of
Expansion
Limits for degree of expansion
**
LL
Remark
PI
Chiro Town Administration to Mticho to Lelia
1
0+000 0+700
0.7
55
23
5
2
Medium
>60
2
1+500 2+100
0.6
55
29
9.4
1.4
Medium
>60
3
2+100 3+000
0.9
63
34
0.9
14.9
high
to
Very high
>60
25- Due
41
to
swell
25- Due
41
2541
to
Swell
&
CBR
Due to LL, PI
Muze tera to TTC to Qilisa road segment
1
0+450 0+700
0.25
62
31
10.3
1
high
>60
2
0+700 1+300
0.6
48
24
5
4
high
>60
3
1+300 1+700
0.4
51
24
4
3
Medium
>60
4
2+400 3+200
0.8
54
23
5.6
2.1
Medium
>60
5
3+200 3+700
0.5
57
28
6.3
2.2
high
>60
6
4+100 6+047
1.947
58-
25-
2.2-
63
32
4.9
2.8-8 high
>60
15- Due
28
2541
to
LL,
PI,
Swell&CBR
Due to Swell &CBR
25- Due to LL, swell&
41
CBR
25- Due to LL, swell&
41
CBR
25- Due to LL, swell&
41
CBR
25- Due to LL, swell&
41
CBR
Hundi gudina School to Nejubas Kidest kidan mihiret Church
0+000 2+536
2.536
54-
23-
7.1-
1.08-
72
38
10.8
2.2
Very high
>60
25- Due
41
to
LL,
PI,swell& CBR
Agricultural research Center to Oda Bultum Universtity to Main Asphalt road
1
0+000 0+400
0.4
2
0+400 1+000
0.6
3
1+000 1+236
0.236
62-
29-
6-
1.4-
high
75
41
11.4
2.42
Very high
62-
29-
6-
1.4-
75
41
11.4
2.42
62
28
9
1
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>60
Very high
>60
Very high
>60
25- Due
41
to
LL,
PI,
swell& CBR
25- Due
41
LL,
PI,swell& CBR
25- Due
41
to
to
LL,
swell& CBR
192
PI,
Expansive(Unsuitable section)
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Hundi gudina School to Aschalew Hotel
1
0+000 0+855
0.855
54-
28-
3.4-
1.4-
64
31
10.8
3.22
Very high
>60
25- Due
41
to
LL,
PI,swell& CBR
Blood bank to Genda to Quteba - Bono
1
0+000 1+022
1.022
52
24
7
1
medium
>60
2
0+000 0+153
0.153
56
25
6
3
medium
>60
3
0+000 0+141
0+141 45
21
2
4
medium
>60
4
0+000 0+214
0.214
52
24
7
1
medium
>60
5
0+000 0+096
0.096
56
25
6
3
medium
>60
Very high
>60
25- Due
41
to
PI,
to
LL,
to
LL,
PI,
swell& CBR
25- Due
41
LL,
PI,swell& CBR
25- Due
41
PI,
swell& CBR
25- Due
41
LL,
swell& CBR
25- Due
41
to
to
LL,
PI,
swell& CBR
Sumeya bridge to Addis ketema Road segment
1
0+000 0+524
0.524
67
36-
8.8-
1.1-
37
9.4
1.4
25- Due
41
to
LL,
PI,
swell& CBR
Agape Hotel to Agricultural research center to TTC Road segment
1
0+000 0+584
Total length
0.584
54-
28-
60
30
11
1.11.4
Very high
>60
25- Due
41
to
LL,
PI,swell& CBR
13.688 Km (67%)
In order to reduce the risk of future effect of the expansive on the performance of the pavement,
the following remedial measures shall be undertaken:
i) Where the finished road level is designed to be less than 2m above ground level, remove the
problem soil to a minimum depth of 600mm over the full width of the road,
j) Where the finished road level is designed to be greater than 2m above ground level, remove
the problem soil to a depth of 600mm below the ground level under the unsurfaced area of the
road structure;
k) The material for replacement shall have minimum four days soaked CBR of not less than 5%
(with two surcharge rings) at a modified AASHTO density of 95% of MDD.
l) After the excavated material has been replaced with non-expansive material in 200mm lift to
95% modified AASHTO density, bring the road to finished level in approved material.
m) Partial replacement of swelling sub grade material with fill quality material and the
replacement thickness is 600mm plus a minimum of 400mm earthwork cover and the width
depending on embankment height,
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n) Provision of slope flattening with side slope (1:4 or 1:6) using the excavated expansive soil
for side fill.
o) Provision of side drain should be avoided unless absolutely necessary. Where it is necessary,
it should be as shallow as possible and as far from the toe of the embankment as possible, as
given in the drawing referred above.
8.5
Near Surface Ground water/ Swampy Section
During reconnaissance survey, there were no swampy areas along and at the sides of the road
project.
8.6
Erodible Soil
Sections where gullies are formed due to severe erosion aggravated by either the nature of the
subgrade material or absence of proper longitudinal drainage systems are identified at a few
locations along the proposed alignment. Hence, gullies may be formed during and after construction
due to disturbance by construction activity.
Table 8- 2: Erodible soil section (Formation of Gully)
Gully Sections
S. No.
Station, Km
Position
Extent, m
dimension,
(deep/wide)
m
Recommendation
Start
End
1
0+500
0+600
RHS
100
1.0/2.0
Treatment method listed below
2
0+950
1+000
RHS
50
1.0/1.0
Treatment method listed below
Figure 8- 1: Erodible soil section (gully section)
The following treatment methods can be employed at where soils are susceptible to erosion
1. If gullies are already formed, they need to be backfilled layer by layer with borrow materials.
2. The side drains (longitudinal ditches) in these section shall be lined irrespective of the
longitudinal slope.
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3. Turn outs shall be constructed in short possible intervals to avoid concentrated flow of water.
Secondary ditches and check dams shall be constructed to dissipate the energy of storm
water running parallel to the road.
4. Proper protection works shall be constructed at culvert inlets and outlets and at approaches.
8.7
Design of Embankments, Cuttings and Retaining Structures
8.7.1
Design of Embankments
The basic geotechnical design issues for fill slope/ embankment include bearing capacity, slope
stability and long and short term settlement. The design issues are often controlled by the
engineering characteristics of the geologic material below the fill rather than property of the fill.
Consequently, geotechnical desk and field study of the project road for fill slope/ embankment focus
on characterization of the existing foundation materials, and engineering design evaluation as how
these existing materials respond to the load from the new fill. If an acceptable response is predicted,
methods of improving the soil below the fill to achieve performance may be required before the fill is
constructed.
The focus of the fill/ embankment design study, however, can be on the embankment fill
performance where embankment side slope is steep in relation to the shear strength of the
anticipated fill material or where light weight fill rather than mineral fill will be used for the
embankment.
For fill/ embankment slope design, the primary design consideration is the potential slope stability
and bearing capacity failures which can occur during construction, causing construction slowdown
and contract claims. Settlements beneath the embankment following construction can result in poor
ride quality of the roadway leading to long term maintenances requirement and premature pavement
failure.
The embankment design is carried out considering the following;
 The required height of embankment and available width for embankment,
 The type of soil supporting the embankment,
 The end of construction, long term operational loading and seismic loading,
 The location of ground water table,
For the design of fill / embankment of the project road, the subsequent design criteria for settlement,
side slope stability and bearing capacity of embankments/ fill slope given in the table below.
Table 8- 3: Design criteria for settlement, side slope stability and bearing capacity of embankments
Design
Component
Mode of Failure
Minimum
Factor
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Vertical
Lateral
Differential
1.1 Local Global Stability 1.3
Unreinforced
Fill slopes
Slopes
1.2 Bearing
Reinforced
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or
Treated Slopes
1.1 Local Global Stability 1.5
Fill slopes
1.2 Bearing Capacity
3.1 Bearing (short term)
3.2 Local & Global Slope
Embankment
on Soft Ground
2.0
Stability (long term)
1.5
1.4
1.2
For the design years post construction
settlement:
(i) within 10m from bridge approach
< 100mm
(ii) road< 250mm
Reinforced Fill
Walls
External Stability
± 5mm per ± 15mm from alignment
/ Internal Stability
metre height
reference
Structures
According to ERA Geotechnical Design manual, embankments over 5m heights are considered as
high fill. For the project road Segments, high fill sections are identified and tabulated below:
Table 8- 4: High fill sections along the road project
Muze tera to TTC to Qilisa road segment
Sumeya bridge to Addis ketema
segment
S.no Station(km)
Fill Height(m)
S.no
Station(km) Fill Height(m)
1
0+260.00
8.168
1
0+840.00
5.251
2
0+280.00
10.485
2
0+860.00
6.906
3
0+300.00
12.354
3
0+880.00
8.395
4
0+320.00
13.514
4
0+900.00
8.982
5
0+340.00
14.775
5
0+920.00
9.352
6
0+360.00
16.655
6
0+940.00
9.501
7
0+380.00
22.169
7
0+960.00
9.344
8
0+400.00
16.27
8
0+980.00
9.481
9
0+420.00
16.854
9
1+000.00
9.822
10
0+440.00
16.653
10
1+020.00
11.871
11
0+460.00
16.166
11
1+040.00
8.491
12
0+480.00
15.711
12
1+060.00
8.011
13
0+500.00
13.887
13
1+080.00
7.287
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0+520.00
11.611
14
Hundi
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1+100.00
gudina
6.201
School
to
Nijubas
15
0+540.00
10.428
Kidest kidan mihiret Church
16
0+560.00
9.047
S.no
Station(km) Fill Height(m)
17
0+580.00
9.041
1
2+500.00
5.787
18
0+600.00
7.341
2
2+520.00
9.77
19
0+620.00
5.291
3
2+540.00
5.916
20
5+120.00
10.867
4
2+560.00
5.885
21
5+140.00
7.063
5
2+580.00
5.727
22
5+160.00
6.035
6
2+600.00
5.635
23
5+420.00
7.475
7
2+620.00
5.364
24
5+440.00
11.009
Chiro Town Administration to Mticho to Lelia
25
5+460.00
16.111
S.no
Station(km) Fill Height(m)
26
5+480.00
19.528
1
3+900.00
5.773
27
5+500.00
9.704
2
3+920.00
7.567
28
5+780.00
13.781
3
3+940.00
6.83
29
5+800.00
7.813
4
3+960.00
5.776
30
5+820.00
4.9
5
3+600.00
6.639
6
3+620.00
11.556
7
3+640.00
13.703
8
3+660.00
11.159
9
3+680.00
5.436
For the high fill sections with the slope of the existing ground greater than 25%, the existing ground
shall be excavated to form horizontal benches. Each bench shall be excavated as the fill material is
compacted and the embankment is raised. Benching shall be a minimum of 3 meters in width in
order to integrate the new embankment with the existing slope. This requirement shall also apply to
embankments constructed on rock.
Table 2. 1: Slope Ratio Table – Vertical to Horizontal
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Note * (1:3 means 1 vertical to 3 horizontal)
** (Flatter slope shall be applied for slide prone back slopes).
8.7.2
Design of Cuttings
The primary geotechnical design criteria for cut slope (both for soil and rock slope) is the stability of
back slope. The stability assessments require characterization of the geologic layers and
groundwater condition of the existing materials.
The geotechnical design activities focus on the evaluation of short and long term stability for different
ground water, material strength and seismic load assumptions. If slope stability is in adequate,
improvement procedures typically involves flattening slopes, drainage improvements and use of
retaining walls or some type of ground improvements.
For cut slopes, a primary design consideration is the potential failures of slopes during construction
or operation which may represent life safety risk. If slope movement are slow, the primary problem
could be long-term maintains requirement to remove earth or rock as it is encroaching on the
roadway.
Generally, because of the inherent variability of geologic materials, the design of each slope is,
however, unique. The design of cut slope for the project road made through acquiring of the
following input data
 A thorough understanding of the surface and sub-surface stratigraphic and geological
structures
 A knowledge of the underground water level, source and flow paths,
 A confident estimate of the probable mode of failure of the cut,
 A reliable estimate of the range of material properties involved in any possible failure,
An acceptable minimum value for the required factor of safety or acceptable risk which takes in to
account the economic consequence of precautionary measure and the consequence of failure.
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Safe Angle of Cut Slope and Berms
The existing natural slope angles represent the maximum stable slope angle for a back slope. The
maximum slope angle and the stable slope height reflect the strength parameters of cohesion and
friction and the ground water conditions as well as the effects of erosion, especially at the toe. The
cut and back slope ratio given in the table below is recommended considering site conditions,
material type and cost.
a)
Unreinforced cuts:
The maximum vertical height of any single continuous cut batter shall, in most cases, not exceed
10.0 m. A minimum 3.0 m wide bench shall be provided for erosion control, control of rock falls and
maintenance purposes at the top of any 10.0 m high single continuous cut batter.
Cuts in readily erodible or dispersive geological materials may require different strategies, e.g.,
flattening without benches.
b)
Reinforced cuts: reinforced (e.g., soil nail/rock dowel walls) cut batter slopes shall not be
steeper than 10 (vertical) to 1 (horizontal).
c)
The cut back slope ratio given in the table below will be repeated after introduction of cut
bench at every 10 meter cut height for soil and weathered rocks. The bench should be 3m wide
and it has a gutter ditch, lined with cement mortar stone pitching or concrete, having 1.0m width,
as shown on drawings.
For the design of cut slopes of the project road, the subsequent design criteria for slope stability
given in the tables below.
Table 8- 5: Design Criteria for Cut Slope Stability
Design
Component
Minimum
Mode Of Failure
Safety
Unreinforced
Local & Global Stability
Slopes
Cut slopes
Reinforced
Treated Slopes
Factor
or Local & Global Stability
(cut & fill slopes)
of
Maximum Permissible Movements
Vertical
Lateral
1.3
1.5
Table 8- 6: Slope Ratio Table – Vertical to Horizontal
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* (1:3 means 1 vertical to 3 horizontal)
** (Flatter slope shall be applied for slide prone back slopes)
8.7.4
Recommended Back Slopes for the Project Alignment
During project site visit, the back slope of the existing road has been evaluated with respect to the
material type on the slope. The material Descriptions along the project road Segments are classified
as below table to recommend for stability of the slopes. The following table gives recommended
back slopes for each road Segments.
Table 8- 7: Recommended back slope ratio
Muze tera to TTC to Qilisa road segment
Sr.
Station Interval
Length
Back
Excavation
No
From
To
Km
Visual Material Description on surface
Slope
type
1
0+000
0+450 0.45
Light grey brown, silty CLAY soil
Earth Slope
Normal
2
0+450
0+700 0.25
Light brown to brown, silty CLAY soil
Earth Slope
Normal
3
0+700
1+300 0.6
Light grey to dark brown, silty CLAY Earth Slope
underlying
by
whitish
grey
intermediate
highly
weathered to decomposed rock
4
1+300
1+700 0.4
Dark brown clay underneath reddish grey Earth Slope
Normal
silty clay soil
5
1+700
2+400 0.7
Moderately to highly weathered rock silty Earth Slope
intermediate
clay soil
6
2+400
3+200 0.8
Light brown to reddish brown silty clay Earth Slope
underneath
Reddish
grey
highly
weathered to Decomposed rock with
gravel
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3+200
Black
3+700 0.5
Black clay to Dark brown clay with silt
cotton Normal
slope
8
3+700
5+100 1.4
Light grey highly weathered rock gravel Earth Slope
intermediate
silty clay soil
9
5+100
6+047 0.947
Dark brown to Black clay underlying brown Black
silty clay soil with gravel
cotton Normal
slope
Kebet tera to Chiro wereda office Road segment
Sr.
Station Interval
Length
Visual Material Description on surface
Back
Excavation
No
From
To
Km
Slope
type
1
0+000
0+700 0.7
Light grey to dark brown, silty CLAY soil
Earth Slope
Normal
2
0+700
1+000 0.3
Light grey, silty CLAY soil underlying silt Earth Slope
Normal
stone
3
1+000
1+238 0.238
Black cotton clay soil
Black
cotton Normal
slope
Sumayo bridge to Addis ketema Road segment Road segment
Sr.
Station Interval
Length
No
From
To
Km
1
0+000
0+524 0.524
Visual Material Description on surface
Back
Excavation
Slope
type
Light grey to dark brown, CLAY soil ‘with Earth Slope
Normal
silty
Agape Hotel to Agricultural research center to TTC Road segment
Sr.
Station Interval
Length
No
From
To
Km
1
0+000
0+584 0.584
Visual Material Description on surface
dark brown to Black , silty CLAY soil
Back
Excavation
Slope
type
Earth Slope
Normal
Agricultural research center to Oda Bultu University to Main Asphalt Road segment
Sr.
Station Interval
Length
No
From
To
Km
1
0+000
0+400 0.4
2
0+400
3
1+000
Visual Material Description on surface
Back
Excavation
Slope
type
dark brown to brown , silty CLAY soil
Earth Slope
Normal
1+000 0.6
dark brown to Black , CLAY soil with silty
Earth Slope
Normal
1+236 0.236
dark brown, CLAY soil with silty
Earth Slope
Normal
Back
Excavation
Slope
type
Chiro Town Administration to Mticho to Lelia Road segment
Sr.
Station Interval
Length
No
From
To
Km
1
0+000
0+700 0.7
Visual Material Description on surface
dark brown to Reddish brown, silty CLAY Earth Slope
Normal
soil
2
0+700
1+000 0.3
Grey highly weathered to decomposed Earth Slope
rock , silty CLAY soil with gravel
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Brown to Light grey ,SILTY CLAY soil Earth Slope
Normal
underlying Reddish grey highly weathered
to Decomposed Rock
4
1+500
2+100 0.6
Reddish grey Decomposed Rock ,SILTY Earth Slope
Normal
CLAY soil overlay with brown clay soil
5
2+100
2+500 0.4
Reddish grey Moderately to
highly Earth Slope
intermediate
weathered Rock gravel SILTY CLAY soil
6
2+500
6+513 4.013
Grey Slightly to Moderately weathered Rock
Hard Rock
Rock underlying Fresh basaltic rock
Hundi gudina to Nijubas Kidest kidan mihiret Church Road segment
Sr.
Station Interval
Length
No
From
To
Km
1
0+000
2+536 2.536
Visual Material Description on surface
light grey to Dark Brown SILTY CLAY soil
Back
Excavation
Slope
type
Earth Slope
Normal
Back
Excavation
Slope
type
Hundi gudina to Aschalew Hotel Road segment
Sr.
Station Interval
Length
No
From
To
Km
1
0+000
0+855 0.855
Visual Material Description on surface
dark brown to Black , CLAY soil with SILT Earth Slope
Normal
Blood bank toGenda to Quteba Bono Road segment
Sr.
Station Interval
Length
No
From
To
Km
1
0+000
1+022 1.022
2
0+000
3
Back
Excavation
Slope
type
dark brown, CLAY soil with SILT
Earth Slope
Normal
0+153 0.153
dark brown, CLAY soil with SILT
Earth Slope
Normal
0+000
0+141 0+141
dark brown, CLAY soil with SILT
Earth Slope
Normal
4
0+000
0+214 0.214
dark brown, CLAY soil with SILT
Earth Slope
Normal
5
0+000
0+096 0.096
dark brown, CLAY soil with SILT
Earth Slope
Normal
8.7.5
Visual Material Description on surface
Method of Rock Excavation
The fact that Chiro town Adminstration to Mticho to Leila Road Segment alignment traverse through
and over the rolling and mountainous section where seismic hazardous of Earthquake expected to
occur in a magnitude of Bed Rock acceleration 0.05 and 0.07 PGA m/s2 from the km 2+500 to Km
6+513 of Road Segment section, the excavation method of hard rock is significant for the instability
of cut slope during and after construction.
There are few sections that required excavation of moderately weathered and fractured rocks which
are indicated in the soil extension given above. These rock masses are easily disturbed during
blasting at the time of construction and by active earthquake after construction. Therefore,
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excavation in moderately weathered and fractured even hard rocks sections need to be carried out
systematically so that the rock mass does not disturbed significantly. Mechanical breaking can also
be used in the case of known instability.
8.7.6
Design of Retaining Structures
Retaining walls are common feature of road construction in mountainous regions. They are
constructed for the following situations:
 to support a road either wholly or partly on fill when the ground profile is too steep
 to support the toe of a slope that has failed or is likely to fail
 to support cut slopes that would otherwise require a gentle, uneconomic angle of cut
 when there are constraints on the permissible plan extent of earthworks, as on hairpin bends,
or hairpin stacks
Three types of retaining walls can be proposed in this project: Mortared masonry retaining wall,
Gabion retaining wall and Reinforced earth retaining walls. The advantage and disadvantage of each
type are presented below:
Mortared Masonry Retaining Walls
Mortared masonry walls are the most durable of the low cost wall options. They are especially suited
to steep rocky ground where foundations are shallow and where the contractor's working area is
restricted. Masonry walls are not tolerant of differential settlement. Their lack of structural flexibility
and general impermeability, even with freely-draining back fill and weep holes, make these walls
inappropriate on wet colluvial slopes and where ground movements are expected.
Considering these characteristics, Mortared Masonry Retaining wall is proposed on fill side where
there is good foundation material with a maximum height of 9m.
Gabion Retaining Walls
Gabion walls are usually preferred under conditions of poor foundation, wet soils, high groundwater
and slope movement due to creep, land sliding and seismicity. Gabion walls have the following
characteristics:
 they can accommodate settlement without rupture
 they allow free drainage through the wall
 they can be constricted in short sections (2-3m at a time) which minimizes the temporary loss
of slope support during excavation
 the shape of a gabion structure can easily be varied to accommodate changes in ground
conditions across the site
 a gabion structure is easy than a masonry structure to fit into an irregular foundation because
of the standard size and rectangular shape of the boxes
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However, the density of gabion work is approximately 70% that of mortared masonry and hence a
gabion wall has to be larger in volume for the same retained height. This increase in size could be a
factor in the choice of wall type in situations where cross-sectional space is limited.
Considering these characteristics, Gabion Retaining wall is proposed on all colluvium/scree deposits
on cut sides where seepage of water is expected. The maximum height of gabion wall shall be 10m.
Gabion retaining walls could also be considered in river training activities and flood protection works.
Slope Protection
Methods of slope protection comprise drainage control and surface treatments for soils and
weathered rock that include masonry revetments and the use of vegetation and less conventional
slope coverings including geotextiles, and bituminous fabrics. Among these, the use of vegetation,
masonry revetments and drainage control are the most common in road construction in Ethiopia.
Vegetation
Vegetation is a very desirable means of providing slope protection for reasons of availability,
relatively low cost, appropriateness of installation techniques and compatibility with a rural
environment. It is particularly appropriate in situations where large areas of slope are affected, a
common situation on road cuttings and over unstable mountain slopes. Vegetation of embankment
slopes is most rapidly achieved by planting with grass slips, by the spreading of collected topsoil
containing roots and seeds. The principal advantages of vegetation from a slope protection point of
view are:
 The presence of a vegetation cover protects the soil against rain splash and erosion, and
prevents the movement of soil particles down slope under the action of gravity.
 Vegetation increases the soil infiltration capacity, helping to reduce the volume of runoff.
 plant roots bind the soil and can increase resistance to failure, especially in the case of loose,
disturbed soils and fills
 plants transpire considerable quantities of water, reducing soil moisture and increasing soil
suction
In view of the above, it is evident that vegetation is important in the control of erosion and shallow
forms of instability, and protect them from scour and disruption, and prevent damage to the slope
generally.
The general characteristics required of bio-engineering plants are:
 they should be adapted to the growing conditions of the general environment, as well as
those of the individual site
 rapid growth
 long-living
 substantial root system
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 easy to propagate
8.7.7
Drainage Controls
Surface drains are frequently constructed on hillsides, for purposes of slope stabilization, together
with berms and/or across the top of a cutting to prevent surface runoff from eroding freshly exposed
materials and to minimize saturation of slopes. In the latter case, they are usually constructed behind
the top of the excavation. They are normally built as a trench, lined with mortared masonry or unlined
depending on the amount of water and soil type.
Factors to be considered in the design of surface drains
 water collected by the drain must be discharged safely, in a manner that will not initiate
erosion elsewhere
 construction of masonry-lined drains should be limited to undisturbed slope materials
 differential settlement, which frequently occurs in man-made ground and particularly at the
interface between natural ground and fill, will lead to rupture
 drain gradients should not exceed 10°
 stepped drain outlets should be provided with a cascade down to the collection point
 drains should discharge into a stream channel wherever possible, and preferably into
channels that already convey a sizeable flow in comparison to the drain discharge
 low points in the drain system should be designed against overtopping by widening or raising
the sidewalls
 lengths of drain should be kept short by the construction of frequent outlets in order to reduce
erosion potential
 Where it is not practicable to discharge cut-off drainage into an adjacent stream channel,
cascades or chutes can be constructed down the cut slope to convey water into the side
drain. However, these structures are often vulnerable to the effects of side splash,
undermining by seepage erosion and concentrated runoff along their margins. They must be
designed to contain the water, and their margins must be protected with vegetation or stone
pitching
In the project road Segments, grouted stone pitched cut-off drains are proposed over erodible soil
sections to minimize erosion and over colluviums section to minimize slope saturation.
8.8
Bridge Foundation Investigation
8.8.1
General
Field investigation for bridge foundation was carried out on major river crossing sites. The objectives
of the investigation are:
 To identify the type, character, and extent of the sub-surface formations prevailing at the
crossing sites,
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 To assess the strength of the foundation materials so that identification and determination of the
bearing layer, bearing depth, allowable soil pressure and type of foundation can be made.
There are Four major crossing sites along the road Segments, as indicated in table below.
Table 8- 8: Lists of Major Crossing Sites
No.
Station
No.of Span
Span Length (m)
Total Length (m)
Name of Road Segment
1
0+210
1
7
7
Sumaeya Bridge to Addis ketema
2
1+055
1
25
25
kebet tera to Chiro woreda office
3
0+345
1
24
24
Muzi tera to TTC to Qilisa
4
5+480
1
10
10
Muzi tera to TTC to Qilisa
5
0+160
1
12
12
8.8.2
Field Investigation
Hundi gudina school to Nejubas
kidest Kidane mihiret Church
During site visit for site investigation work, locations of the bridge crossings were inspected and
relevant data to help assess the foundation condition of the bridge locations has been collected.
Only field observation has been carried out for this Design report. Detail investigation shall be carried
out during construction phase.
It was observed that the foundation of bridges at km 0+210, km 1+025, km 0+420 and 0+160 are
bedded Segmented fine to course Sandstone gravel with silt overlain by dark to Light grey brown
silty clay soil and foundation of bridges at km 5+480 is bedded Sedmented fine to course gravel with
Sand silt overlying by light brown silty clay soil. There is an existing bridge at km 0+210 and km
1+055.
Bridge Crossing at Km 0+420 and km 5+480 for Muzi tera to TTC Road Segment
This the first major river crossed by the road alignment. The stream is characterized by a trapezoidal
shaped valley with medium deep banks. The bank material on both sides is Light grey brown to
brown silty clay soil and sedmented round gravel. There is no existing bridge at this location.
The second major river crossing stream is characterized by a trapezoidal shaped valley with a
shallow bank. The bank material on both sides is Sedmented fine to course gravel with sand silt
overlying by light brown to Reddish brown silty clay soil. Large basaltic cobblestone rocks are
observed at the bed of the river. There is no existing bridge at this location.
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Figure 8- 2: River crossing at Km 0+420 Figure 8- 3: River crossing at Km 5+480 (chiro River
(chiro River side bank)
side bank)
Bridge Crossing at Km 1+025 for kebte tera to Chiro wereda office Road Segment
This is the only major river crossed by this road Segment. The stream is characterized by a
trapezoidal shaped valley with medium deep banks. The bank material on both sides is Light grey
brown to brown silty clay soil and sedmented round gravel. There is an existing bridge at this
location. The condition of the sub structure is Fair to poor; no cracks are observed on the abutment
and scouring is noted.
Figure 8- 4: River crossing at Km 1+055
Bridge Crossing Km 0+210 for to Sumeya Bridge to Addis ketema Road Segment
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This is the only major river crossed by this road Segment. The stream is characterized by a
trapezoidal shaped valley with medium deep banks. The bank material on both sides is Light grey
brown to brown silty clay soil and sedmented round gravel. There is an existing bridge at this
location. The condition of the sub structure is Fair to poor; no cracks are observed on the abutment
and scouring is noted
Figure 8- 5: River crossing at Km 0+210
Bridge Crossing Km 0+160 for Hundi gudina School to Nejubas Kidest Kidane mihiret
Chuech Road Segment
This is the only major river crossed by this road Segment. The stream is characterized by a
trapezoidal shaped valley with medium deep banks. The bank material on both sides is Light grey
brown to brown silty clay soil and sedmented round gravel. There is an existing bridge at this
location. The condition of the sub structure is Fair to poor; no cracks are observed on the abutment
and scouring is noted
Figure 8- 6: River crossing at Km 0+160
DCP Testing
The Dynamic Cone Penetrometer (DCP) was initially developed in South Africa for in-situ evaluation
of pavement (Kleyn, 1975). Since then, it has been widely used in all over the world for site
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characterization of subsurface materials. The DCP has proven to be an effective tool in the
assessment of in-situ strength of pavement and subgrade in highway construction. DCP testing has
also been used for borrow pit location and determination of overburden thickness. DCP is typically
used in horizontal construction applications, such as pavements, building, Bridges, Culvert’s
foundation and floor slabs.
Standard DCP apparatus with the following features has been used during the site investigation.
•
8 kg hammer freely falling from a height of 575 mm
•
60° cone having a diameter of 20 mm
•
Extension rods
The DCP is held vertically and the test is conducted by dropping the hammer from 575 mm. While
the cone penetrates through the ground, the depth of penetration with set number of blows was read
in mm from a fixed meter ruler. The number of blows has been adjusted depending on the resistance
of the ground under testing. Then the penetration rate, PR (sometimes referred as DCP ratio, or
penetration index PI) is calculated. The DCP ratio is defined by the slope of the curve relating the
number of blows to the depth of penetration (in mm/blow) at a given linear depth segment.
Figure 8- 7: Schematic representation of DCP
DCP tests were conducted on both abutments of the Bridge foundation positions. The test locations
were excavated on each abutments sides that are besides of the existing structures of a rectangular
area having 2m X 2m X 2m dimensions. Moreover, DCP testing was conducted inside test pit
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excavated after excavated 2m depth of the top soil. DCP tests conducted in the bottom layer are
ended up with refusal in some pits and considered as N-50.
Bearing Capacity Recommendation and Analysis of bridge
Bearing Capacity Analysis from DCP
This section focuses on comprehensive description and explanation of the outcomes of subsurface
investigations based on visual observation, test pitting, DCP test and bearing capacities
computations. To measure the in situ strength of the sub surface material of the Bridge’s foundation,
DCP tests were carried out in each test pit position.
The choice of a particular type of foundation depends on the magnitude of the structural loads, the
nature of the subsurface strata and loading. In terms of their seating depths within subsurface, these
are categorized as shallow and deep (pile) foundations. For reasons of economy, shallow foundation
is the first logical choice unless it is considered inadequate bearing capacity. As far as the shear
strength of the foundation layers of the Bridge considered as determined from DCP testing and
visual observation, all of the foundation grounds of the proposed Bridge can accommodate shallow
foundations.
The allowable bearing pressure is the maximum net intensity of loading that can be imposed on the
soil with no possibility of shear failure or the possibility of excessive settlement.
The outcome from the DCP test is intended to measure the ground resistance and converted it into
SPT N-30 (number of blows required to penetrate 30cm during Standard Penetration Test) using the
correlation developed by TRRL, Overseas Road Note-9, Design of Small Bridges 1992 or TRL, A
Design Manual for Small Bridges, 2000. Accordingly, mm/blow obtained from DCP test can be
converted into SPT N-30 by the following formula (N-30) is limited to a maximum of 50. The result of
the DCP test is plotted using excel where by layers with nearly similar resistance have been
identified.
N-30 = 240.88*(mm/blow) ^- 0.97
Table 8- 9: Typical Correlation between DCP and SPT-N Values
DCP value mm/blow
5
6
7
8
9
10
12
14
16
18
20
SPT value blows/300mm
50
44
38
33
28
24
22
18
16
15
14
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Figure 8- 8: Graphic form of DCP to SPT N-30
The summaries of the ground resistance as measured by DCP tests and converted into an
equivalent N-30 is shown in Tables below and the plot of penetration resistance; total blows against
depth are included as annex.
Table 8- 10: Summaries of DCP test results and SPT N-values of each Bridge
Staio
n
Pit
Name
Road segments
of Locati
on
Start
side
0+34
5
Muzi tera to TTC
to Qilisa
End
side
5+48
0
Layer
s
Depth
from
top(m)
Layer
Average
Thickne
penetration
ss(mm)
(mm)/blow
DCP
CBR
TO
SPT
1
0.85
915
15.09
17.15 17.44
2
1.76
915
11.73
22.37 22.58
3
2.68
4
126.3 121.2
1830
2.28
5
3
3.59
1830
3.16
89.62 86.86
5
4.01
2250
3.92
71.20 69.47
1
0.85
915
16.90
15.21 15.53
2
1.76
910
10.58
24.95 25.10
3
2.27
1425
8.50
31.4
31.43
0.85
920
22.37
11.3
11.65
Design
SPT
30
26
Start
side
Rock
End
1
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2
1.07
215
7.68
35.0
34.88
1
0.84
910
23.89
10.5
10.89
203.1
Start
side
0+21
Sumeya
Bridge
0
Addis ketema
to
End
side
Start
1+05
Kebet tera to Chiro side
5
woreda Office
2
1.77
930
1.38
215.1 9
121.5
3
2.75
1899
2.27
126.7 6
4
3.65
1821
3.21
88.0
85.34
5
4.02
2269
3.84
72.8
70.99
1
0.80
910
9.13
29.2
29.21
2
1.84
910
8.94
29.8
29.86
3
2.70
1815
9.84
26.9
27.06
4
3.57
1820
7.71
34.9
34.73
5
4.32
2565
7.65
35.1
35.00
1
0.91
905
14.60
17.8
18.05
2
1.82
910
8.58
31.1
31.11
3
1.99
1080
7.29
37.0
36.78
1
0.5
495
9.90
26.8
26.88
1
0.85
915
21.13
12.0
12.35
2
1.63
910
13.24
19.7
19.94
130.6
Start
side
0
32
31
End
side
0+16
30
Hundi gudina school
to Nejubas kidane
mihiret
3
2.54
1830
2.12
136.5 6
4
3.82
2185
3.25
86.9
84.33
5
4.16
2170
3.99
70.0
68.30
1
0.85
915
10.30
25.7
25.80
2
1.84
990
13.38
19.5
19.73
113.5
End
side
3
2.75
1830
2.43
118.1 1
4
3.67
1905
3.23
87.4
84.72
5
4.58
2740
4.15
67.2
65.65
27
30
30
According to the DCP data analysis, the bearing capacities most of the Bridge are very high value
due to the presence of coarse-grained material makes irregularities of the ground. Thus, average of
the N-30 value used for safe design (N-55). The outcome from the DCP test is intended to measure
the ground resistance and converted it into SPT N-30 (number of blows required to penetrate 30cm
during Standard Penetration Test) using the correlation developed by bowls 1997, 5th edition. Thus,
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bearing capacity of the subsurface materials are computed based on the DCP N-30 values obtained.
The summaries of the test results are presented in the table 3-2 above. The bearing capacity
computations are addressed in detail as follows.
q a ( kPa ) 
N
K d , B ≤ F4
F1
2
N  B  F3 
q a (kPa )  
 Kd
F2  B 
, B > F4
Where, qa = Allowable Bearing Capacity for 25mm settlement in KPa
Kd = 1+0.33D/B < 1.33
F2 = 0.08
F3 = 0.3
F4 = 1.2
B = Width of foundation
D = Depth of Footing in m
As far as settlement is concerned, the Bowels method is empirically obtained for a settlement of 1”
(25mm).
Table 8- 11: Summary of bearing capacity Obtained from DCP Test for each Bridge based on N55
Staion, Road
Km
segment
Name
0+420
1+055
Recommended
Width, m
Depth, m
2
Start
Qall in KPa @
side
3.0m
End
Qall in KPa @
Muzi tera to TTC side
3.0m
to Qilisa
Start
Qall in KPa @
side
2.0m
End
Qall in KPa @
side
2.0m
Start
Qall in KPa @
5+480
0+210
Position
Sumeya
Bridge side
to Addis ketema
3.0m
End
Qall in KPa @
side
3.0 m
Kebet tera to Chiro Start
2.5
3
3.5
4
4.5
5
5.5
6
660 626 603 567 541 521 505 492 482
580 550 531 499 475 458 444 433 424
660 595 554 525 505 489 477 467 459
541 487 454 431 414 401 391 383 376
660 626 603 567 541 521 505 492 482
709 672 649 609 581 559 542 529 518
Qall in KPa @ 681 646 623 586 558 538 521 508 497
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Staion, Road
Km
0+160
segment
Name
Position
Recommended
Width, m
Depth, m
2
woreda
side
3.0 m
Office
End
Qall in KPa @
side
3.0m
Hundi
gudina Start
school
to side
Nejubas
kidane End
mihiret
side
8.9
Qall in KPa @
3.0m
Qall in KPa @
3.0m
2.5
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3.5
4
4.5
5
5.5
6
591 561 541 508 484 466 452 441 432
660 626 603 567 541 521 505 492 482
660 626 603 567 541 521 505 492 482
Conclusion
Based on the analyses and interpretations made so far, the Geotechnical parameters are presented
in table 3-6 above. As a whole the formation in the study area is soil with insignificant to significant
variation in soil strengths. The allowable pressure, for the selected bearing layer and depth is
determined by analysis of field DCP N value taking the minimum safe value.
if unforeseen weak soil or expansive clay material is encountered during construction, replace the
foundation material with a CBR Value Greater than or equal to 30% Sub-base material and then
compacted to 97% of the MDD at each compacted layer with a thickness of 20cm to avoid a
possibility of differential settlements due to void spaces inside the gravel /boulder’s material.
However, the structural engineer can choose among the given list of bearing capacity in table 3.3
above to meet his requirement with the appropriate footing width and depth of foundation.
Furthermore, the geo-technical Engineer in charge of the project may alter (increase or decrease)
the level of footing recommended here based on the actual material type to be revealed/
encountered during excavation.
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9
STRUCTURAL DESIGN
9.1
General
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Structures in road projects mainly consist of drainage structures and retaining walls for stability of
slopes. They are one of the most important elements of road construction. The serviceability of a
road is highly influenced by the absence of proper drainage structures and lack of properly located
stabilizing structures. They mainly include culverts, bridges, energy dissipation structures and
retaining walls.
Highway Drainage facilities are designed to convey predetermined discharges in order to avoid a
significant flood hazard on the road. The hydrological and hydraulic analyses for the section of the
road project have been conducted through careful examination, review and analysis of the relevant
hydro-metrological data, topographical maps, aerial photographs and other imageries.
Accordingly, there are 71 drainage structures in all road segment. Of these, 5 are Bridges, 12 are
reinforced concrete slab culverts, and the remaining 54 are reinforced concrete pipe culverts.
9.2
Structures Design Standard
The design of the bridges is conducted based on AASHTO LRFD Bridge Design Manual 2013 and
the new Ethiopian Roads Authority Bridge Design Manual (ERA BDM-2013) which has been recently
developed based on AASHTO LRFD Bridge Design Specification, 2004.
As per ERA BDM-2013, the design vehicle load for maintenance and extension of existing bridges
shall be HS-25 and HL-93 for the design of new bridges. The new Vehicular load, HL-93, consists of
“Design Truck” or “Design Tandem” loaded simultaneously with lane load.
9.2.1
Methodology
The Bridges are designed for specified limit states to achieve the objectives of constructability, safety,
and serviceability, with due regard to issues of ease for inspection, economy, and aesthetics.
The design is based on Load and Resistance Factor Design (LRFD), as presented in the both
Specifications. Load and Resistance Factor Design (LRFD) takes into account both the statistical
mean resistance and the statistical mean loads. The fundamental LRFD equation includes a load
modifier (η), load factors (γ), force effects (Q), a resistance factor (φ), a nominal resistance (Rn), and
a factored resistance (Rr = φRn). LRFD provides a more uniform level of safety throughout the entire
bridge, in which the measure of safety is a function of the variability of the loads and the resistance.
The substructure is designed to sustain all the worst conditions imposed by the load multiplied by the
applicable load factors. Foundation is designed to support all loads in accordance with general
principles specified in the references for strength and stability.
9.2.2
Loading
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Based on the requirements of the ERA Bridge Design Manual - 2013, the following permanent and
transient loads and forces are considered in the design.
9.3
Permanent Loads
a. Dead load of structural components and non-structural attachments (DC).
As the structures are constructed with reinforced concrete and stone masonry, this load is dead load
of concrete (unit Weight 24KN/m3) and Masonry (unit Weight 27KN/m3).
b. Dead load of wearing surfaces and utilities (DW).
Bituminous Wearing surfaces have been assumed on deck surfaces as a wearing surface (unit
weight 22.5 KN/m3) for future provisions.
c. Vertical pressure from dead load of earth pressure (EV).
Rolled Gravel or Hand Laid Rock Ballast as earth fill material is assumed (unit weight taken is 19.5
KN/m3).
d.
Horizontal Earth pressure Load (EH).
Lateral earth pressure is assumed for walls backfilled with earth. The walls are reviewed and
designed assuming that they can move away from the soil mass. The coefficient of lateral earth
pressure will be determined from the permitted backfill materials.
9.4
Transient loads
As per ERA BDM-2013, and ASHTO LRFD 2004 the design vehicle load for the design of new
bridges shall be HL-93 for. The new Vehicular load, HL-93, consists of “Design Truck” or “Design
Tandem” simultaneously loaded with a lane load. Whichever design loadings creating the maximum
effect was considered in the design of the bridges. Axle weights and spacing axles as specified in
ERA Bridge Design Manual -2013.
a. Designs truck Load.
Total of design truck is 325 KN distributed between 3 axles. Front axle loading is 35KN and two rear
axles loading is 145 KN each. Distance between front and first rear axle is 4.3m. The distance
between two rear axles varies from 4.3 to 9m to produce extreme force effects.
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Figure 9- 1: Designs truck
b. Design tandem load.
Design tandem load is exceptional loading and shall be applied for military vehicle loading and for
strategic bridges. Design tandem comprised of a pair of 110KN axles spaced at 1.2m. Each axle
comprised of two wheels spaced at 1.8m transversely.
Figure 9- 2: Designs tandem
c. Design Lane Load.
Design lane load consist of 9.3 KN/m, uniformly distributed longitudinally. Transversely, the load is
assumed to occupy a 3.0m width.
d. Pedestrian load.
A pedestrian load of 4 KN/m2 is applied to all walkways wider than 0.6m. They are considered to act
simultaneously with the vehicular design live load.
9.5
Environmental Effects
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Environmental effects are those resulting from natural effects such as wind, temperature and seismic
events.
a) Wind
It has been assumed that the base wind speed for structures (VB) is 145 km/h.
b) Temperature
A temperature range from 5o to 35oC has been assumed in the design of critical elements. For the
calculation of effects due to temperature gradients through superstructures the appropriate values
are:
T1 = 35oC, T2 = 10oC, T3 = 5oC
c) Seismic Effects
The project traverses in the areas of the country defined as zone 0, which is the lowest seismic
activity region. As a result, seismic analysis is not required but minimum support width of 0.5m will
be adopted at all connections.
d) Water Loads
Longitudinal Stream Pressure
The pressure of flowing water acting in the longitudinal direction of substructures shall be taken as:
p = 5.14*10-4 CDV2 (3.9)
Where: p = pressure of flowing water (MPa)
CD = drag coefficient for piers as specified in Table 11.1
V = design velocity in m/s of water for the design flood in strength and service limit states and
for the check flood in the extreme event limit state (see ERA Drainage Design Manual-2013, Chapter
5: Hydrology).
Table 9- 1:: Drag Coefficient
Type
CD
Semi-circular-nosed pier
0.7
Square-ended pier
1.4
Debris lodged against the pier
1.4
Wedged-nosed pier with nose angle 90o or less
0.8
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The longitudinal drag force shall be taken as the product of longitudinal stream pressure and the
projected surface exposed thereto. Where a significant amount of driftwood is carried, water
pressure shall also be considered for on a driftwood raft lodged against the pier.
Lateral Stream Pressure
The lateral, uniformly distributed pressure on substructure due to water flowing at an angle, θ, to the
longitudinal axis of the pier (see Figure 11-3) shall be taken as:
PL = 5.14 x 10-4CLV2 (3.10)
Where: PL = lateral pressure (MPa)
CL = lateral drag coefficient specified in Table below.
Figure 9- 3: Plan View of Pier Showing Stream Flow Pressure
Table 9- 2: Lateral Drag Coefficient
Angle  between direction of flow and longitudinal axis of the pier
CL
0o
0.0
o
1
0.5
10o
0.7
20o
0.9
>30o
1.0
The lateral drag force shall be taken as the product of the lateral stream pressure and the surface
exposed thereto.
9.5.1
Materials
The structural materials generally used for design of structures in this project are reinforced concrete
and stone masonry.
Concrete and masonry are the preferred material for construction of Bridges and culverts; however,
other materials may be more suitable for a particular location, hydraulic roughness, bedding
condition, or project. In evaluating the suitability of alternate materials, the selection process was
based on a comparison of the total cost of alternate materials over the design life of the structure
that is dependent upon the following:
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 Durability (service life),
 Cost
 Availability
 Construction and maintenance ease
 Structural strength,
 Traffic delays and
 Water tightness requirements.
I.
Reinforced Concrete
Grade of concrete: C30, Fck (150mm cubes) = 30MPa at 28 days. ---For main part of structures
C20, Fck (150mm cubes) = 16MPa at 28 days. ---For footing pad of small height walls
C15, Fck (150mm cubes) = 15MPa at 28 days. ---For levelling concrete
Other design properties of concrete are used as stated on ERA bridge design Manual -2013 (chapter
-7: reinforced concrete)
Reinforcement Steel minimum nominal yield strength of deformed bars: AASHTO M31 M Grade 40 (300 MPa Yield strength)
AASHTO M31 M Grade 60 (420 MPa Yield strength)
II.
Stone masonry
According to ERA standard technical specification-2013, stone masonry is divided into three classes.
However; the consultant has used Class B stone masonry for the construction of major and minor
watercourse crossing structures. This grade of stone masonry shall conform to the requirement of
ERA standard technical specification – 2013.
9.6
Structure Type Selection
The type of drainage structure specified for this project is determined based on economic,
topography, hydrologic and hydraulic considerations. Minor drainage structures are used where
major drainage structures are not hydraulically required, where debris is tolerable, and where they
are more economical than a bridge.
The type of drainage structure appropriate to each crossing is recommended. Structures of less than
6m span are designed as minor drainage structures and structures of 6m and above were to be
designed as major drainage structures.
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To arrive at a safe and economical crossing location, the Consultant has considered the following
conditions
 Straight reach of the river.
 Location beyond the disturbing influence of large tributaries.
 Well-defined and stable high banks.
 Economical and straight approach road.
 Location that permits square crossing.
 Less river training works.
 Good foundation condition.
 Shortest possible span.
Considering the above conditions, the selection task consisted of desktop studies for possible
crossing sites. These possibilities are later checked and confirmed on actual field conditions before
the final selections were made.
Five of the major crossings are designed as a slab bridge and RC deck girder. The substructures of
the major crossing are selected to be masonry type to reduce the construction cost and difficulty
because the maximum height required is less than 9m, which is the limit for masonry substructure
The superstructures at two of the major crossings at 1+120 and 0+378 are RC Deck-Girder type
spanning 18m, and 24m simply supported in single span arrangements. The remaining three of the
major crossing at 5+280, 0+167 and 0+418 are slab bridge type in single span arrangement. None of
the major crossings are skewed and a straight reach was attained. All the crossings were selected at
better foundation, narrow locations requiring lesser river training work.
9.7
Structural Evaluation of Existing Structures
9.7.1
Major and Minor Drainage Structures
Road segment 1 Musitera-TTC Road
In this existing road segment, there is an existing double pipe culvert and two new single span
bridges found. The bridges were not under constructed yet.
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Road segment 2 Kebit Tera Chiro Wereda Asitedader
Within this road segment there is an existing 10m triple footbridge or a pedestrian bridge. This
footbridge has a 3m carriageway width and the structure is deteriorated which makes it substandard
for the new design. Other than these structures, the road has no existing crossing drainage
structures.
Road segment 3 Sumeya Bridge Addis ketema
In this road segment there is an existing skew slab bridge structure and one new single span bridge.
The bridge was not under constructed yet.
Road segment 4Agape-TTC Road
This road segment has no existing cross-drainage structures. Therefore, the design might consider
drainage structures.
Road segment 5 Agricultural Research Odu- Bulitu University Road
This road segment has no existing cross-drainage structures. However, the design might consider
drainage structures.
Road segment 6 Chiro Ketema Asitedader -Medirilo Kutir 2 Road
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This road segment has one single span RC slab culvert with 6m wide carriage width and no sidewalk
width on both sides. The superstructure and substructure are not good. Therefore, as per the
hydraulics study finding a new slab culvert will be designed.
9.8
Detail Design
9.8.1
Bridges
The design process is totally based on the design standard and methodology described on the
previous subchapter. During the preliminary design stage different superstructure and substructure
types with different arrangements were investigated to arrive at the safest, feasible and economical
layout, and in the final stage the best one is detailed with maximum possible accuracy.
A lot of geometric revisions were communicated with the highway engineer to make the bridges
safer, feasible and economical. And in process the finished grade levels were needed to be raised at
some crossings below. There are many structural designs and analysis for the crossings, retaining
wall and protection works but among the major components that needed design are:  12m and 24m Reinforced Concrete Deck-Girder Superstructure and 7m Slab Bridge
 Masonry Abutment, Wing-wall and Pier with their foundations
Superstructures are designed with Class-A C-30 concrete reinforced with mild steel and High-Yield
steel. All superstructures designed as per the typical drawings having the necessary carriageways,
median and walkways and protected by Class-Y reinforced concrete RC railing.
9.8.2
Culverts
Minor Drainage structures are concrete box culverts, Slab Culverts and reinforced concrete pipe
culverts. Basically standardization of design has to be adopted for minor drainage structures. The
standard drawings are prepared based on the standard drawings provided in ERA SDD 2013.
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Selection between box and slab culverts is made based on the foundation material description
provided by the geotechnical engineer at crossing site. According to the sub grade extension
reported by the material engineer if the type of the martial where the rectangular culverts lie is weak
soils, then Box culverts will be recommended.
The selection of end structure for pipe culverts is generally dependent on factors such as the
condition of the approaching channel, slope and stability of the outlet channel. The culvert inlet type
shall be selected from standard details from the Standard drawing prepared by the consultant based
on ERA’s Standard Detail Drawings. Erosion protection will be recommended in consideration to the
hydrologist recommendation, invert slope and natural ground inlet and outlet condition of the culvert,
those recommendations are presented and quantified on the culvert schedule and culvert crosssection drawing.
9.9
Structures in the Project
9.9.1
Major Structures
There are five major crossings in this project which singly supported simple spans superstructures
composed RC Deck-Girder. All abutments are proposed to be made of masonry except the height of
the abutment exceeds 9m.
Table 9- 3: Schedule of Major Structures
Road
No.
1
2
Name
Span
No. of Clear
Span
Height
Superstructure
0+378
24m
1
6m
RC Deck Girder
5+280
12m
1
4m
RC Deck Girder
woreda 1+020
18m
2
5.5m
RC Deck Girder
0+167
7m
1
5m
Slab Bridge
0+418
14m
2
4m
RC Deck Girder
to Qilisa
Muzi tera to TTC
to Qilisa
Chiro
Arrangement
Station
Muzi tera to TTC
Kebet
3
segment
tera
to
Office
4
5
Sumeya
Bridge
to Addis ketema
Hundi
gudina
school
to
Nejubas
kidane
Substructure
Masonry Abutment and
Wing-wall
Masonry
Abutment,
Wing-wall and Pier
Masonry Abutment and
Wing-wall
Masonry Abutment and
Wing-wall
Masonry Abutment and
Wing-wall
mihiret
*Span rearranged from hydraulic recommendation for structural standard and construction simplicity
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9.9.2
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Minor Structures
Along the project route, 66 crossings have been recommended for minor drainage structures by the
hydrologist. Of which 54 is Reinforced Concert pipe culverts and the remaining are adopted as either
Reinforced Concert Box or Reinforced Slab culverts. Almost all of the existing culverts are replaced
mainly due to hydraulic inadequacy because they are mostly silted up.
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10 UTILITIES AND PRIVATE ACCESSES
10.1 Utilities
The type and number of utilities which will be affected by the construction work is presented as
shown in table below
Table 10- 1: Utilities along the project road
Sewerage Water line
Street code Street name
1
Muz tera –TTC-Qilisa
2
Kebt tera-Chiro Wereda Office
3
Sumeya Bridge-Addis Ketema
4
5
6
7
Electric line (EL)
tension line
Electric poles & High
Electric poles & High
tension line
TTC
tension line
Agri Reserch Center-ODA Bultu
Electric poles & High
University-Main Asphalt
tension line
Chiro Town Administration-Mtichu-
Electric poles & High
Leila
tension line
Hundi Gudina Scl-Nejebac Kidane
Electric poles & High
Mihret
tension line
9
Blood Bank-Gende Kuteba Bono
10
Chiro Wereda Office – Care Ethiopia
Water Line
tension line
Electric poles & High
Hundi Gudina Scl-Aschalew Hotel
(WL)
Electric poles & High
Agape Hotel-Agri Reserch Center-
8
line (SL)
Electric poles & High
tension line
Electric poles & High
tension line
Electric poles & High
tension line
10.2 Private Accesses
In the project road, there are no private accesses that are affected by the construction work.
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