TECTONICS ENGINEERING AND CONSULT LTD.
GEOTECHNICAL SOIL REPORT
BAUCHI STATE UNIVERSITY
SEPTEMBER 2014
GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHIKARRI ROAD,BAUCHI.
GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
TABLE OF CONTENTS
Cover page ...................................................................................................................................................
Table of Contents .......................................................................................................................................1
List of Tables ...............................................................................................................................................2
List of Plates .................................................................................................................................................2
List of Figures ..............................................................................................................................................3
Executive Summary......................................................................................................................................4
CHAPTER ONE INTRODUCTION
1.1 General Background .............................................................................................................................5
1.2 Scopes of work ......................................................................................................................................5
1.3 Brief Description of the Site ………………………………………………………………6
CHAPTER TWO FIELD AND LABORATORY WORKS
2.1 Surface Exploration .............................................................................................................................8
2.2 Subsurface Exploration .......................................................................................................................8
2.2.1 Dynamic Cone Penetrometer Test ....................................................................................8
2.2.2 Test Pitting ............................................................................................................................9
2.2.3 Hand Auger Sampling .........................................................................................................9
2.2.4 Table of test pit coordinates ..........................................................................................10
2.2.5 Pictures showing exploratory activities .........................................................................14
2.2.6 Pictures showing DCP tests .............................................................................................15
2.3 Laboratory Testing...............................................................................................................................16
2.3.1 Natural Moisture Contents................................................................................................16
2.3.2 Particle size analysis ...........................................................................................................16
2.3.3 Atterberg Limits .................................................................................................................16
2.3.4 Direct Shear Test ................................................................................................................17
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
2.3.5 Consolidation Test …………………………………………………………17
2.3.6 Plate showing laboratory test in progress................................................................18
CHAPTER THREE RESULTS AND DICUSSION
3.1 Natural Moisture Contents ................................................................................................................19
3.2 Particle Size Analysis ..........................................................................................................................19
3.3 Atterberg Limits ..................................................................................................................................19
3.4 Soil Classification Criteria ..................................................................................................................20
3.5 Direct Shear Test ................................................................................................................................20
3.6 Bearing Capacity .................................................................................................................................21
3.7 Consolidation test ...............................................................................................................................22
3.8 Dynamic Cone Penetration Test Results ........................................................................................23
CHAPTER FOUR SUMMARY AND CONCLUSION
4.1 General Conclusions ..........................................................................................................................24
4.2 Recommendations .............................................................................................................................24
4.3 Limitations ..........................................................................................................................................24
REFERENCES
…………………………………………………………………………. 26
LIST OF TABLES
Table 2.1 Coordinates and Elevations of DCP/Test Pits ……………………………………..
Table 3.1 Summary of Test Results ………………………………………………………….
Table 3.2 Laboratory Bearing Capacity ………………………..……………………………..
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
Table 3.3 DCP Bearing Capacity Results ............................................................................................
LIST OF PLATES
Plate I: Showing Excavation/soil sampling at the Proposed Site …………………………….
Plate II: Laboratory Activities at Tectonics Engineering & Consults Ltd, Abuja ……………..
LIST OF FIGURES
Plate I: Showing the site’s Layout …………………………………………………………..
APPENDICES
……………………………………………………………………………
APPENDIX A ................................................................................Natural Moisture Contents
APPENDIX B ..................................................................................Particle Size Analysis Graphs
APPENDIX C.................................................................................. Atterberg Limits Results
APPENDIX D ..................................................................................Direct Shear Graphs
APPENDIX E ................................................................................... Consolidation Test Plots
APPENDIX F...................................................................................DCP Bearing Capacity Plots
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
EXECUTIVE SUMMARY
The subsurface exploration and geotechnical engineering services requested for the site of
Bauchi State University along Bauchi-Karri road have been completed. Subsurface conditions at
the subject site were explored by 120 (One hundred and twenty) test pits taken to a depth of
1.5m each. The results of the sampling and the coordinates of its approximate locations are
included in this report.Also,twenty points were tested for in-situ bearing capacity values with the
use of the dynamic cone penetrometer (DCP). This report describes the subsurface conditions
encountered in the explorations, presents the test results obtained, and provides
recommendations for use in designing of structural foundations.
The soils underlying the site are classified based on Unified Soil Classification System (USCS) for
the proposed area.Soils recording more than 50% of its particle passing sieve #200 is considered
fine – grained soil while those below 50% are classified as coarse-grained. Based on this criteria,
the soils underlying the site are predominantly coarse – grained. The group symbol of the soil is
SM with group name silty sand with gravel.
The soil strenght values were determined with the use of Direct Cone Penetrometer (DCP) and
the allowable bearing pressures determined by direct shear tests in the lab. The values from the
DCP range from 66kn/m2 and 418kn/m2 while the allowable pressures from the direct shear
tests range from 60kn/m2 and 240kn/m2. It is to be noted that areas nearer to the streams are
the ones with the lower bearing values as informed by their moisture content and their particle
size gradations.Based on the results above,60kn/m2 is therefore recommended as the bearing
capacity of the site and can be used for design purposes.
The compressibility assessment of the soil indicates a range of coefficient compressibility range
of 0.011m2/MN and 0.38m2/MN.Areas with low compressibility values fall under the category
of “Very slightly compressible” materials while those above 0.35m2/MN are “Very highly
compressible” soils.As a result,those areas nearer to the streams are very highly compressible and
structures to be built in such areas recquire rigorous analysis and standard construction methods
as primary settlement should be anticipated on the areas.
Based on the results of our findings, the following are hereby recommended:

A bearing capacity value of 60kN/m2 at 1.5m depth was established for the site and can
be used for design purpose.


A dry unit weight of 18.6 kN/m3 may be used for design purpose.
The foundation types to be used depend on the complexity of the intended structures
and anticipated loadings.The engineering judgement of a registered structural engineer is
of importance since the strenght values and their corresponding compressibilities vary
due to the size of the site.Isolated pad foundations would suffice for the areas with low
compressibilities while foundation beams and raft foundation would be recquired in
places with low bearing capacities and high compressiblities.Tables showing locations
and their values are included in this report.
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
CHAPTER ONE
INTRODUCTION
1.1 General Background
Successful engineering projects often involves the use of engineering principles in the
appropriate manner which in turn answers concerns such as safety and economy. Such concerns
includes and is not limited to a proper understanding of site conditions on which projects are to
be built. To this end, Tectonics Engineering & Consults Ltd was commisioned to investigate the
proposed land belonging to Bauchi State University along Bauchi-Karre road Bauchi for site
exploration and characterisation.This process involved a two-part program of tests performed
on the site insitu properties ,also known as field tests and laboratory analysis .
Samples were taken at detailed positions and locations and further logged on which series of
tests were performed on in the laboratory.Various field methods were employed in acquiring
relevant data on the site vis-a-vis Dynamic Cone Penetration Test and Hand Auger method
along with Test Pitting in collecting the soil samples.
The present assessment is conducted to present in details the findings on the underlying soil
properties of the proposed Bauchi state university for the purpose of design and execution by
employing relevant and reliable techniques. One hundred and twenty test pits were sampled and
properly logged and twenty points were tested for in-situ bearing capacities determination.Each
split-barrel sample was tested to determine the moisture content, Atterberg limits tests were
performed on a representative soil sample to aid in soil classification. All laboratory testing was
performed in general accordance with appropriate standards. The results of these laboratory tests
are reported on approriate tables including their respective sample location.
The DCP test equally gave on indication of the site underlying soil as the penetrations recorded
against each hammer blow was found to be low with depths of refusal ranging between 0.8m and
2.7m.
1.2 Scopes of Work

To conduct Dynamic Cone Penetrometer Test (DCP) on twenty locations of the site for
in – situ bearing capacity determinations.

To obtain undisturbed/disturbed samples through accessible exploration methods by test
pits and sampling.
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.

To evaluate by conducting laboratory tests the physical properties and strength of the
soils obtained for both disturbed and undisturbed samples from the test pits.
1.3 Brief Description of the Site
The proposed site is located in Bauchi state along Bauchi-karri road in the northern part of the
country. The site was covered with vegetation at the time this exploration was conducted. The
study area has a gentle, undulating topography characterized by relatively high ground from the
northern part that slopes gently towards the southern part of the area.
The area lies within the Borno basin and it is underlain by Pleistocene sedimentary rocks of the
Chad Formation, which consists of yellow, grey clay, fine to coarse-grained sand with
intercalations of sandy clay, gravels and diatomites. The Chad Formation is underlain by the
basement rocks at the periphery of the basin and underlain by Kerrikerri Formation and Fika
Shale towards the shallow part of the basin and towards the basin centre respectively.
The soil formation in the project area is predominantly coarse-grained with a high content of
gravel,silt and clay in varying combinations resulting in medium to low strength values.
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
SITE LAYOUT/SATELLITE IMAGERY
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
CHAPTER TWO
FIELD AND LABORATORY WORKS
2.1 Surface Exploration
The investigation involved surface exploration. The consultant’s team traversed the entire site
and the surroundings noting its features and existing structures.
2.2 Subsurface Exploration
The field crew visited the site in August, 2014 for field explorations, logging and sampling.
The explorations included surface, accessible exploration methods by test pits and sampling and
DCP. Various soil samples were collected. These samples were examined visual manually for
possible identification and were transported to the Laboratory for further analysis.
The twenty (20) points of the DCP were found to record refusal at a minimum depth of 0.8m
and maximum of 2.7m. It was therefore evident that the sites at the areas farther from the
streams have low DCP values indicating high strenght while those close to the streams show low
strenght values.
2.2.1 Dynamic Cone Penetrometer (DCP) Test
Dynamic Cone Penetration (DCP) Test involves driving a solid cone of 600 into the ground,
using repeated blows of a hammer with a fixed mass of 8Kg falling through a distance of 575mm
having maximum diameter of 20mm. The hammer strikes an anvil which is rigidly fixed to the
rods which are of smaller diameters than the cone, and transmit the hammer energy to it.
As the cone was being driven into the ground, the number of blows required to drive each
increment (typically 100 mm) was being recorded. The point of refusal was recorded and the test
terminated at depths where hammer blows greater than 50 caused less than 100mm penetration.
The blow count is inputted in to appropriate software to provide a more-or-less continuous
profile of penetration resistance with depth and consequent determination of the bearing
capacity usually at 0.5m depth interval.
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
It is to be noted that the rods are generally quite short, and as each new rod was added
they are usually being turned through one or more revolutions, in order to reduce
friction.
2.2.2 Test Pits
The test pits were generally located at 120 locations within the site. The pits were
excavated by hand in order that the soil could be examined in situ and samples taken.
Topsoil was stripped from the pit area before the start of the work and was stockpiled
separately until completion.
2.2.3 Hand Auger Sampling
Hand auger was used by two men, who press down on the cross-bar as they rotate it thus
advancing the hole. Once the auger was full, or has collected sufficient material, it was
brought back to the surface and the soil removed.
The hand auger samples were recommended for the borrow pit areas where the samples
were collected at 1.0 – 2.0m maximum depths.
It is rule of thumb that in stiff or very stiff clays, hand-auger progress will be very slow,
and the depth of boring may have to be limited to about 5 m or less. When such clays
contain gravel, cobbles or boulders it will not normally be possible to advance the hole at
all. In uncemented sands or gravels, it will not be possible to advance the hole below the
water table, since casing cannot be used and the hole will collapse either on top of the
auger (which makes it difficult to recover the auger from the hole) or when the auger is
being removed. Only samples of very limited size can be obtained from the hole.
Table 2.1 presents the coordinates and elevations of the test locations
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
Table 2.1 Coordinates of DCP/Test Pits
BAUCHI STATE UNIVERSITY
TP
NOS
NORTHINGS
EASTINGS
TP1
TP2
TP3
TP4
TP5
TP6
TP7
TP8
TP9
TP10
TP11
TP12
TP13
TP14
TP15
TP16
TP17
TP18
TP19
TP20
10° 22' 78.1"
10° 22' 7.78"
10° 22' 7.55"
10° 22' 7.36"
10° 22' 7.06"
10° 22' 6.66"
10° 22' 7.41"
10° 22' 7.91"
10° 22' 8.43"
10° 22' 5.43"
10° 22' 9.46"
10° 22' 9.99"
10° 22' 0.45"
10° 23' 0.98"
10° 23' 0.84"
10° 23' 1.57"
10° 23' 1.46"
10° 23' 1,.29"
10° 23' 0.89"
10° 23' 0.46"
009°55' 92.9"
009°55' 8.86"
009°55' 8.31"
009°55' 6.89"
009°55' 3.67"
009°55' 3.32"
009°55' 2.83"
009°55' 3.62"
009°55' 4.35"
009°55' 5.43 "
009°55' 6.31"
009°55' 7.62"
009°55' 7.94"
009°55' 8.79"
009°55' 9.44"
009°55' 9.64"
009°55' 8.47"
009°55' 7.93"
009°55' 7.40"
009°55' 6.45"
TP21
TP22
TP23
TP24
TP25
TP26
TP27
TP28
TP29
TP30
TP31
TP32
TP33
TP34
TP35
TP36
TP37
TP38
10° 23' 0.05"
10° 22' 9.91"
10° 22' 9.50"
10° 22' 9.40 "
10° 22' 9.04"
10° 22' 9.92"
10° 23' 0.16"
10° 23' 0.68"
10° 23' 1.10"
10° 23' 1.30"
10° 23' 1.68"
10° 23' 2.00"
10° 23' 2.67"
10° 23' 3.01"
10° 23' 2.43"
10° 23' 2.32"
10° 23' 2.32"
10° 23' 2.63"
009°55' 5.67"
009°55' 4.85"
009°55' 3.77"
009°55' 2.81"
009°55' 2.37"
009°55' 2.52"
009°55' 3.12"
009°55' 3.56"
009°55' 4.18"
009°55' 4.51"
009°55' 5.08"
009°55' 5.95"
009°55' 6.67"
009°55' 7.33"
009°55' 7.59"
009°55' 8.19"
009°55' 8.68"
009°55' 9.04"
ELEVATION
(m)
REMARK
565
Not far from road
568
567
564
563
564
568
567
569
571
570
567
566
569
564
561
565
565
566
568
568
569
569
564
558
560
561
560
562
562
563
563
561
560
560
559
564
560
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
TP39
TP40
TP41
TP42
TP43
TP44
TP45
TP46
TP47
TP48
TP49
TP50
TP51
TP52
TP53
TP54
TP55
TP56
TP57
TP58
TP59
TP60
TP61
TP62
TP63
TP64
TP65
TP66
TP67
TP68
TP69
TP70
10° 23' 3.20"
10° 23' 0.04"
10° 23' 3.96"
10° 23' 4.18"
10° 23' 4.29"
10° 23' 4.42"
10° 23' 4.27"
10° 23' 4.05"
10° 23' 3.95"
10° 23' 3.31"
10° 23' 3.21"
10° 23' 3.10"
10° 23' 3.08"
10° 23' 3.32"
10° 23' 3.64"
10° 23' 3.85"
10° 23' 3.96"
10° 23' 4.14"
10° 23' 4.27"
10° 23' 4.70"
10° 23' 5.19"
10° 23' 5.43"
10° 23' 5.95"
10° 23' 6.13"
10° 23' 6.43"
10° 23' 6.70"
10° 23' 6.98"
10° 23' 7.18"
10° 23' 7.35"
10° 23' 7.59"
10° 23' 7.91"
10° 23' 8.22"
009°55' 9.86"
009°55' 0.04"
009°55' 0.46"
009°55' 0.02"
009°55' 9.42"
009°55' 8.67"
009°55' 7.62"
009°55' 6.47"
009°55' 6.02"
009°55' 4.92"
009°55' 3.60"
009°55' 2.92"
009°55' 2.52"
009°55' 1.85"
009°55' 1.59"
009°55' 1.93"
009°55' 2.29"
009°55' 2.76"
009°55' 3.13"
009°55' 3.53"
009°55' 4.48"
009°55' 4.61"
009°55' 4.86"
009°55' 5.02"
009°55' 5.26"
009°55' 5.53"
009°55' 5.84"
009°55' 6.08"
009°55' 6.44"
009°55' 6.65"
009°55' 7.08"
009°55' 7.85"
557
556
553
555
559
558
560
563
564
561
558
556
556
553
552
552
553
551
553
553
552
552
552
552
551
551
551
551
549
555
555
558
TP71
10° 23' 6.75"
009°55' 7.85"
558
close to rock
TP72
TP73
TP74
TP75
TP76
10° 23' 7.04"
10° 23' 7.18"
10° 23' 7.13"
10° 23' 7.14"
10° 23' 7.44"
009°55' 7.70"
009°55' 8.25"
009°55' 8.43"
009°55' 8.96"
009°55' 9.02"
557
554
553
550
551
close to rock
TP77
TP78
10° 23' 7.02"
10° 23' 7.21"
009°55' 9.64"
009°56' 0.24"
551
551
Close to stream
TP79
10° 23' 7.44"
009°56' 0.57"
553
Road track
TP80
TP81
TP82
10° 23' 7.77"
10° 23' 8.02"
10° 23' 7.85"
009°56' 0.46"
009°56' 0.31"
009°55' 9.89"
552
551
551
Road track
Close to footpath
Close to rock
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
TP83
10° 23' 8.02"
009°55' 9.64"
550
TP84
TP85
TP86
TP87
TP88
TP89
10° 23' 7.92"
10° 23' 8.10"
10° 23' 7.93"
10° 23' 8.59"
10° 23' 8.67"
10° 23' 8.72"
009°55' 9.20"
009°55' 8.75"
009°55' 8.44"
009°55' 7.75"
009°55' 7.33"
009°55' 7.04"
550
551
552
552
551
551
Close to track road
TP90
10° 23' 9.22"
009°55' 7.83"
549
Close to rock
TP91
TP92
TP93
TP94
TP95
10° 23' 89.57"
10° 23' 9.65"
10° 23' 9.39"
10° 24' 0.07"
10° 24' 0.07 "
009°55' 7.71"
009°55' 7.13"
009°55' 6.62"
009°55' 6.78"
009°55' 6.39"
547
548
549
547
546
Close to rock
TP96
10° 24' 0.66"
009°55' 6.53"
547
stream and rock
TP97
10° 24' 1.07"
009°55' 6.90"
544
Close to rock
TP98
TP99
TP100
TP101
10° 24' 1.12"
10° 24' 1.02"
10° 24' 0.39"
10° 24' 0.37"
009°55' 7.23"
009°55' 7.55"
009°55' 7.25"
009°55' 7.94"
543
545
548
548
Close to rock
TP102
TP103
TP104
10° 24' 0.63"
10° 24' 1.45"
10° 24' 2.20"
009°55' 8.04"
009°55' 8.77"
009°55' 8.78"
547
546
543
Close to track road
TP105
TP106
TP107
TP108
TP109
TP110
TP111
TP112
TP113
TP114
TP115
TP116
TP117
TP118
TP119
TP120
10° 24' 2.57"
10° 24' 2.67"
10° 24' 9.36"
10° 24' 2.19"
10° 24' 1.93"
10° 24' 0.09"
10° 24' 1.27"
10° 24' 0.84"
10° 24' 0.46"
10° 24' 0.04"
10° 24' 9.74"
10° 24' 1.33"
10° 24' 9.76"
10° 24' 9.24"
10° 24' 9.19"
10° 24' 9.04"
009°55' 8.92"
009°55' 9.36"
009°55' 9.77"
009°56' 0.02"
009°55' 0.39"
009°56' 0.09"
009°55' 9.71"
009°56' 0.07"
009°56' 0.45"
009°56' 0.85"
009°56' 1.08"
009°56' 1.33"
009°56' 1.87"
009°56' 0.25"
009°55' 9.31"
009°55' 8.93"
542
541
542
544
544
544
545
545
546
547
549
550
549
551
548
549
Close to track road
Page - 12 -
GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
BAUCHI STATE UNIVERSITY
TP
NOS
NORTHINGS
EASTINGS
ELEVATION
(m)
POINT 1
10° 23' 2.69"
009° 55' 7.34"
562
POINT 2
POINT 3
POINT 4
POINT 5
POINT 6
POINT 7
POINT 8
POINT 9
POINT
10
POINT
11
POINT
12
POINT
13
POINT
14
POINT
15
POINT
16
POINT
17
POINT
18
POINT
19
POINT
20
10° 23' 3.89"
10° 23' 3.79"
10° 23' 3.39
10° 23' 4.06"
10° 23' 3.97
10° 23' 4.29"
10° 23' 4.71"
10° 23' 5.51"
009°55' 7.09"
009°55' 6.36"
009°55' 6.19"
009°55' 5.86"
009°55' 4.43"
009°55' 3.86"
009°55' 3.53"
009°55' 3.34"
562
563
563
562
556
554
553
550
10° 23' 6.12"
009°55' 4.05 "
550
10° 23' 6.49"
009°55' 4.58"
549
10° 23' 6.56"
009°55' 5.31"
541
10° 23' 6.46"
009°55' 6.12"
553
10° 23' 6.16"
009°55' 6.61"
560
10° 23' 6.68"
009°55' 6.99"
551
10° 23' 5.40"
009°55' 7.13"
560
10° 23' 5.17"
009°55' 77.6"
559
10° 23' 4.67"
009°55' 8.38"
558
close to gully
10° 23' 4.09"
009°55' 9.01"
558
close to gully
10° 23' 3.00"
009°55' 7.95"
560
REMARKS
Close to footpath
Page - 13 -
GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
Field team digging
for test pit
samples.
Hand auger used
to extract samples .
Page - 14 -
GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
Plate I PICTURES Showing Exploratory Activities on the Site
In-situ bearing
capacity
determination test
in progress.
Page - 15 -
GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
Engineer taking
notes of number of
blows recorded.
Plate 2 PICTURES Showing Field tests in progress on the Site
2.3 Laboratory Testings
The following tests were conducted on the collected samples for the purpose of soil
classification and design:

Natural moisture content

Particle size analysis

Atterberg limits (Liquid limit, plastic limit)

Direct shear test

Consolidation
2.3.1 Natural moisture content
Water is present in most naturally occurring soils. The amount of water expressed as a
proportion by mass of dry solid particles known as the moisture content has a profound effect
on soil behaviour. Moisture content is regarded as a guide to classification of natural soils and
is measured for most samples used for most field and laboratory tests.
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2.3.2 Particle size analysis
The individual solid particles in a soil can have different sizes and shapes, and these
characteristics also have a significant effect on its engineering behaviour. Therefore,
geotechnical engineers often assess the distribution of particle sizes in a soil and the shapes of
the particles in the soil.
Particle size analysis expresses quantitatively the proportion by mass of the various sizes of the
particles present in the soil. A distribution analysis is a necessary index test for soils especially
coarse-grained soils, in that it presents the relative proportions of different sizes of particles.
From this, it is possible to tell whether the soil consists of predominantly gravel, sand, silt or
clay sizes and to a limited extent which of the sizes range is likely to control the engineering
properties.
2.3.3 Atterberg Limits
Liquid limit, plastic limit and shrinkage limit are known as the Atterberg Limits. These are used
to assess the plasticity of a fine-grained soils and its consistency at various moisture contents.
The liquid limit is the empirically established moisture content at which a soil passes from the
liquid state to the plastic state. It provides a means of classifying a soil especially when the
plastic limit is also known.
The plastic limit is the empirically established moisture content at which a soil becomes too dry
to be plastic. It is used together with the liquid limit to determine the plasticity index which
when plotted against the liquid limit on the plasticity chart provides means of classifying a
cohesive soil.
Shrinkage due to drying is significant in clays but less so in silts and sands. These tests enable
the shrinkage limit of clays to be determined. i.e the moisture content below which a clay ceases
to shrink. They also provide ways of quantifying the amount of shrinkage likely to be
experienced by clays in terms of shrinkage ratio, volumetric shrinkage and linear shrinkage.
2.3.4 Direct Shear Test
The drained shear strength (effective stress analysis) is of most importance for granular soils.
The shear strength of granular soils is often measured in the direct shear apparatus, where a soil
specimen is subjected to a constant vertical pressure while a horizontal force is applied to the
top of the shear box so that the soil specimen is sheared in half along a horizontal shear
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surface. By plotting the vertical pressure versus shear stress at failure, the effective friction
angle as well as effective cohesion can be obtained.
2.3.5 Consolidation Test
The consolidation test (also known as oedometer test) is the primary laboratory test used to
study the settlement and expansion behaviour of soils. The consolidation test should only be
performed on undisturbed soil specimens, or in the case of studies behaviour, on specimens
compacted to anticipated field and moisture condition.
In order to evaluate the suitability of a foundation or earth structure, it is necessary to design
against both bearing capacity failure and excessive settlement. For foundations on cohesive soils,
the principal design criterion is typically the latter - the control of expected settlements within
the limits considered tolerable for the structure. As a result, once allowable foundation
displacements have been established, the estimate of total settlement over the service life of the
structure is a major factor in the choice of foundation design.
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
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Plate 3: Laboratory Activities at Tectonics Engineering & Consults Ltd, Abuja.
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
ROAD,BAUCHI.
CHAPTER THREE
RESULTS AND DISCUSSION
All the laboratory tests were conducted in the Soil and Material laboratory of Tectonics
Engineering & Consults Ltd, Abuja. The tests were performed in accordance with relevant BS
Codes of practice and are as presented below:
3.1 Natural Moisture Content
The soil specimens collected from the site were carefully preserved for the determination of
the moisture contents. The test was conducted following the specifications spelt in BS 1377:
Part 2: 1990, where the oven drying method was used. The range of the values obtained from
the test is of the order of 3.3% - 12.8% for the test pits.
Table 3.1 shows the summary of the results while Appendix A presents the detail results.
3.2 Particle size analysis
The test was conducted in accordance with BS 1377 part 2: 1990. The detailed results are
presented in Appendix B.
The gradation test results indicated that the bulk of the soils to be predominantly coarse grained as evident from the estimate of the percentage passing sieve #200 even though a few
fall in the category of fine-grained soils. These generally range between 4.4% and 68.4%.
These according to USCS are largely considered coarse – grained soils.
The summary of the gradation test results are presented in Table 3.2; while the details are
shown in the Appendix B.
3.3 Atterberg Limits
These were also performed in line with the specification of BS 1377 part 2: 1990. The results
are presented in Appendix C.
The liquid limit test was conducted using the Casagrande liquid limit apparatus. The majority
of the results obtained for the test pit samples showed non – plastic and low to medium
plasticity values in consonant with the sieve results.
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
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3.4 Soil Classification Criteria
The soils underlying the site are classified based on Unified Soil Classification System (USCS)
for the proposed building area. The former assumes soil having liquid limit greater than 50
and/or plasticity index in excess of 30 to be of high plasticity. While soil recording more than
50% of its particle passing sieve #200 is considered fine – grained soil. Based on these
criteria, the soils underlying the site are predominantly coarse - grained . The group symbol of
the soil is SM which is silty sand with gravel.
3.5 Direct Shear test
The direct shear test was conducted in accordance with BS 1377: Part 7: 1990. The cohesion
for the test pits recorded 1.2KN/m2 to 39.2 KN/m2 while angle of repose are between 5.50
and 21.40. Detailed results of the test are presented in Appendix E. But the summary is as
presented in Table 3.2 below.
3.6 Bearing Capacity
The estimate of the bearing capacity of the collected soil specimens became necessary having
obtained the requisite parameters from the analysis conducted so far. In order to avoid the
attainment of limit state of the structures due to foundation failure, efforts are made to come
up with allowable bearing pressures for various trial pits to ensure that the shear stresses in
the soils do not exceed the shear strength of the soils in question.
To achieve this, the following bearing capacity equations for shallow foundations for a
uniform vertical loading assuming a general shear failure as developed by Terzaghi (1943)
which are the most commonly used equations are as given below:
𝑞𝑢𝑙𝑡 =
𝑄𝑢𝑙𝑡
𝐵𝐿
1
= 𝑐𝑁𝑐 + 𝛾𝐷𝑓 𝑁𝑞 + 2 𝛾𝐵𝑁𝛾 ...............................for strip footing
𝐵
𝑞𝑢𝑙𝑡 = 𝑐𝑁𝑐 (1 + 0.3 𝐿 ) + 𝛾𝐷𝑓 𝑁𝑞 + 0.4 𝛾𝐵𝑁𝛾 .....for square/rectangular footings
𝑞𝑢𝑙𝑡 = 1.3𝑐𝑁𝑐 + 𝛾𝐷𝑓 𝑁𝑞 + 0.3 𝛾𝐵𝑁𝛾 ...................for circular footing
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𝑁𝑐 = (𝑁𝑞 − 1) cot 𝜑
φ
𝑁𝑞 = tan2 (450 + ) e(πtanφ)
2
𝑁𝛾 = 1.5(𝑁𝑞 − 1) tan 𝜑
Where qult = ultimate bearing capacity (kN/m2)
c’ = cohesion of the soil underlying the footing (kN/m2)
B = width of footing (m)
L = length of footing (m)
γ = total unit weight of soil (kN/m3)
Df= vertical distance from ground surface to bottom of footing (m)
Nc, Nq, N‫ =ץ‬dimensionless bearing capacity factors
qult= Qult/BL
Where Qult= vertical concentric load causing a general shear failure of the underlying soil
(kN/m2)
Allowable bearing capacity is given as:
𝑞𝑎𝑙𝑙 =
𝑞𝑛𝑒𝑡
𝐹
+ 𝛾𝐷𝑓
Where F = factor of safety which is usually taken as 3.
The Bearing Capacity values obtained for all the Test Pits are shown in the table below:
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
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Table 3.2: Test Pits Allowable Bearing Pressure from Laboratory Results
TP
NO.
Depth
(m)
C'
(KN/m2)
φ'(0)
γb
(KN/m3)
5
13
15
17
18
46
57
60
68
76
81
93
118
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
21.2
6.9
39.2
12.5
4.8
1.2
24.8
3.8
6.6
14.6
25.8
18.2
24.4
7.4
21.4
5.5
24.8
25.7
21.9
11.6
8.6
22.6
17.7
20.2
9.6
7.3
22.0
22.0
22.0
18.6
21.0
21.0
21.0
19.1
18.6
21.0
21.0
21.0
19.1
Nc
Nq
Nγ
7.30 1.95 0.18
16.23 7.36 3.74
6.65 1.64 0.09
20.43 10.44 6.54
21.78 11.48 7.57
16.77 7.74 4.07
9.09 2.87 0.57
7.76 2.17 0.27
17.57 8.31 4.57
12.87 5.11 1.97
15.02 6.53 3.05
8.17 2.38 0.35
7.27 1.93 0.18
qnet
(KN/m2)
FOS
qall
(KN/m2)
220
395
315
607
545
306
321
93
389
368
624
226
233
3
3
3
3
3
3
3
3
3
3
3
3
3
106
165
138
230
213
133
138
60
158
154
240
107
106
3.7 Consolidation
The consolidation test performed was one – dimensional consolidation test and was
conducted in accordance with clause 3 of BS 1377: Part 5: 1990. The consolidation test
results show the soils to be highly compressible iin some areas and slightly compressible in
other areas.Attached in this report are results of the oedometer tests.The values of the ratio
of cc/1+e0 are found to range between 0.011 and 0.38. The detailed results of the tests are as
outlined in Appendix G.
3.8 Dynamic Cone Penetrometer (DCP) Test
The trends of the Bearing Capacity obtained from the DCP generally fluctuate with depth in
most cases.A value of 60kN/m2 is determined for the site.This in line with standard practice
may be considered for design purpose which may prove adequate to safely support the
anticipated load from the building .
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
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Table 3.2: Bearing Capacity Determination from DCP
Depth (m)
P1
P2
P3
P4
P5
P6
P7
P8
P9
P10
P11
P12
P13
P14
P15
P16
P17
P18
P19
P20
0.5
21
92
46
108
27
68
65
70
92
78
21
158
58
87
40
65
68
183
250
98
1.0
127
56
75
268
105
74
119
164
150
94
161
173
172
151
105
98
170
358
464
214
1.5
198
66
145
355
112
255
2.0
2.5
102
137
159
219
190
231
287
206
183
190
269
419
303
369
411
285
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
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CHAPTER FOUR
SUMMARY AND CONCLUSION
4.0 General Conclusions
The geotechnical investigation for the site of Bauchi State University along Bauchi –karri road
was successfully completed by Tectonics Engineering and consults and the results are detailed in
this report.
The soils underlying the site are classified based on Unified Soil Classification System (USCS) for
the proposed building area; this assumes soil having liquid limit greater than 50 and/or plasticity
index in excess of 30 to be of high plasticity. While soil recording more than 50% of its particle
passing sieve #200 is considered fine – grained soil. Based on these criteria, the soils underlying
the site are predominantly coarse – grained because they generally fall in the latter category. The
group symbol of the soil is SM which is silty sand With gravel .The compressibility assessment of
the soil suggests highly compressible property therefore all structures are expected to be
designed to structural adequacy in line with standard engineering practices and procedures. Also,
primary consolidation settlement is anticipated.
4.1 Recommendations Based on the results of our findings, the following are hereby
recommended:

A bearing capacity value of 60kN/m2 at 1.5m depth was established for the site.

A dry unit weight of 18.6kN/m3 may be used for design purpose.

The foundation types to be used depend on the complexity of the intended structures
and anticipated loadings.The engineering judgement of a registered structural engineer is
of importance since the strenght values and their corresponding compressibilities vary
due to the size of the site.Isolated pad foundations would suffice for the areas with low
compressibilities while foundation beams and raft foundation would be recquired in
places with low bearing capacities and high compressiblities.Tables showing locations
and their values are included in this report.
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
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4.2 Limitations
Finally, it should be noted that the results and recommendations of this report are solely
the based on the in – situ tests conducted and the collected soil samples within the days
of the site visit and assuming that the subsurface conditions do not significantly deviate
from those encountered. Geotechnical investigation involves gathering and assimilation
of limited facts about the nature of subsoil in order to understand and predict their
nature in a particular site and under certain conditions. Hence, results obtained are only
directly relevant to the subsoil conditions at the time the investigation was conducted. As
a result, any interpretation or recommendation given in this report is based on judgment
and experience and not on the greater knowledge of the entire site conditions.
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GEOTECHINICAL REPORT FOR BAUCHI STATE UNIVERSITY ALONG BAUCHI-KARRI
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REFERENCES:
1. D. P. Donald, M. R. Yeung and W. A. Kitch; (2011): Geotechnical Engineering,
Principles and Practices
Publisher: Pearson, Second Edition. California.
2. C. A. Kogbe; (1989): Geology of Nigeria
Publisher: Rock View (Nigeria) Limited, Second Revised Edition. Jos, Nigeria.
3.
BS 1377: Parts 2,3,4,5 & 7 of 1990
4. BS 8004 of 1986 and BS 5930 of 1992.
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APPENDICES
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