Blackhead Consulting (Pty) Ltd
Tel : 011 958 0054
Email : hiltonsparks@blackhead.co.za
GAUTENG DEPARTMENT OF
HUMAN SETTLEMENTS
DIEPSLOOT EAST EXT 0
ENGINEERING SCHEME REPORT ROADS
AND STORMWATER
TITLE
GAUTENG DEPARTMENT OF HUMAN
SETTLEMENTS
DIEPSLOOT EAST EXT 0
ENGINEERING SCHEME REPORT ROADS AND
STORMWATER
CLIENT
Gauteng Department of Human Settlements
14th Floor
1066 Building
35 Pritchard Street
Johannesburg
Tel: +27 11 630 5000
PREPARED BY :
Blackhead Consulting (Pty) Ltd
9 Willowbrook Office Park
Van der Kloof Street
Ruimsig
1732
DATE
09/01/2014
REFERENCE NUMBER
2014/001
Engineering Scheme Report Roads and Stormwater
PROJECT TEAM
H D N Sparks
__________________
PR Eng No 740604
REVISION
1
DATE
9 JANUARY 2014
DESCRIPTION
ORIGINAL
TABLE OF CONTENTS
1. INTRODUCTION ............................................................................................................................................ 5
2. DESCRIPTION OF SITE.................................................................................................................................. 6
2.1. EXISTING DEVELOPMENT ON SITE ................................................................................................................... 6
2.2. TOWN PLANNING .............................................................................................................................................. 6
3. INVESTIGATIONS .......................................................................................................................................... 7
3.1. GEOTECHNICAL INVESTIGATION ........................................................................................................................ 7
3.1.1. SITE GEOLOGY ................................................................................................................................... 8
3.1.2. FOUNDATION SOLUTIONS ................................................................................................................... 8
3.2. TRAFFIC IMPACT ASSESSMENT ......................................................................................................................... 9
3.3. FLOODLINES .................................................................................................................................................... 9
4. EXISTING AND PROPOSED SERVICES .......................................................................................................... 10
4.1. STORMWATER ................................................................................................................................................ 10
4.1.1. EXISTING SYSTEM .............................................................................................................................. 10
4.1.2. PROPOSED STORMWATER SYSTEM..................................................................................................... 10
4.2. ROADS. ......................................................................................................................................................... 11
4.2.1.
4.2.2.
4.2.3.
4.2.4.
4.2.5.
4.2.6.
4.2.7.
NEW EXTERNAL ROADS ..................................................................................................................... 11
NEW INTERNAL ROADS ...................................................................................................................... 11
PAVEMENT DESIGN ............................................................................................................................ 11
TYPICAL CROSS SECTION .................................................................................................................. 12
PUBLIC TRANSPORT.......................................................................................................................... 12
REFUSE AREA ................................................................................................................................... 12
SUB‐SURFACE DRAINS ...................................................................................................................... 12
5. COST ESTIMATES ...................................................................................................................................... 13
5.1. ROADS ......................................................................................................................................................... 13
5.2. STORMWATER ................................................................................................................................................ 13
5.3. SUMMARY OF COST ESTIMATES ...................................................................................................................... 14
6. BULK SERVICE CONTRIBUTIONS ................................................................................................................. 15
6.1. ROADS AND STORMWATER ............................................................................................................................. 15
LIST OF TABLES
Table 1 – Proposed Land Uses ...................................................................................................................7
Table 2 - Stormwater Design Parameters and Standards .......................................................................10
Table 3 - Geometric Requirements for Internal Roads ...........................................................................11
Table 4 - Road Pavement Designs ............................................................................................................11
Table 5 - Parking Area Pavement Designs ...............................................................................................12
Table 6 - Cost Estimates Roads ................................................................................................................13
Table 7 - Cost Estimate Stormwater .........................................................................................................13
Table 8 - Summary of Cost Estimates ......................................................................................................14
APPENDIXES
1.
INTRODUCTION
Blackhead Consulting (Pty) Ltd was appointed by the Client, Gauteng Department of
Human Settlements, as the Civil Consulting Engineers for the compilation of an
Engineering Scheme Report for Diepsloot East Ext 0. The purpose of this report is to
establish the civil services and material and design standards for the proposed
development as required by the Johannesburg Roads Agency (JRA), a utility of the
City of Johannesburg (CoJ).
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2.
DESCRIPTION OF SITE
The site is located east of the Diepsloot Township on portion 119 of the farm
Diepsloot 388 JR, as shown below.
FIGURE 1 – LOCALITY PLAN
2.1.
EXISTING DEVELOPMENT ON SITE
There are no existing developments on the site.
2.2.
TOWN PLANNING
Table 1 below shows the proposed land uses for the township.
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TABLE 1 – PROPOSED LAND USES
Land Use
Area (ha)
Special
Institutional
Private Parking
Public Open Space
Roads
Total
No of stands
40,96
10,40
1,00
6,41
2,77
73,24
39
3
4
3
49
Figure 2 below shows the township layout
FIGURE 2 – TOWNSHIP LAYOUT
The township layout will be amended to take into account Environmental
issues, and the requirements of the Client.
3.
INVESTIGATIONS
3.1.
GEOTECHNICAL INVESTIGATION
Africa Exposed Consulting Engineering Geologists conducted the geotechnical
investigation for the Diepsloot East Ext 0 proposed development. The objectives of
the geotechnical investigation were to give information and recommendations on the
following issues:


Recommendations on the most suitable foundations for new structures;
Recommendations on the suitability of in situ material for road and pavement
construction, terraces and general earthworks;
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

Presence of groundwater and the recommendations on how to deal with it during
construction and operation of the development; and,
Comments of any geotechnical features that may influence the construction and
operation of the development.
Refer to the geotechnical report prepared by Africa Exposed Consulting Engineering
Geologists for specific information on the geotechnical investigation methodology.
3.1.1.
Site Geology
The site geology is underlain by coarse gritty quartzite of the Langlaagte Quartzite
formation, Johannesburg Subgroup, Central Rand Group, Witwatersrand
Supergroup. Large portions of the site are underlain by poor selected fill to a depth
of 2,4 m thick with a loose to very loose consistency and consist of abundant
fragment in a matrix of ash. Natural occurring transported soils were identified below
the fill. This hillwash consists of fine colluvial sands and clayey silts of alluvial origin
that occur to a depth of up to 2,0 m below ground level. The area on the western
side of the site is underlain by a wetland, which has been altered and modified by
development in the vicinity. The transported soils are underlain by residual silty
sandy soils which are derived from the in situ decomposition of the quartz bedrock.
The upper horizons which include the imported fill and the transported soils,
including the pebble marker that occurs at an average depth of 1,0 m, will be
collapsible and compressible and the underlying residual quartzite that occurs
beyond this depth will be marginally compressible.
3.1.2.
Foundation Solutions
The foundation solution for each of the zones:
3.1.2.1.
Zone S1
The foundation solution for heavy structures in this zone should be founded on
deep pads or strip footings that can be placed on the dense to very dense residual
quartzite or the very soft rock quartzite at an average depth of 1,2 m below the
current ground level. Bearing pressures have to be limited to 150 kPa. The
foundation solution for light structures can be placed on modified normal strip
footings. The external and internal walls of the structures must be founded on
reinforced strip footings that can be placed at an average depth of 0,8 m below
ground level. The foundations must be reinforced and construction may proceed with
brick force included between each course in the plinth wall for a minimum of 6
courses. Articulation joints must be included at all external and internal doors and
openings. Particular attention must be placed on drainage precautions and ensuring
the competence of water bearing services. Bed preparation must be done by the
removal of in situ soils to a depth of 450 mm and replaced in 150 mm thick layers with
the same excavated material, compacted to 93% of Mod AASHTO. Bearing
pressures to be limited to 50 kPa.
Under individual footings the in situ soils have to be removed to a depth 1,5 times
the foundation width or to a competent horizon. Excavated material must be replaced
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in 150 mm thick layers with the same excavated material which is compacted to
93% Mod AASHTO. Bearing pressures have to be limited to 80 kPa.
3.1.2.2.
Zone C2
For modified normal strip footings all the external and internal walls are founded on
reinforced strip footings placed at an average depth of 0,8 m below ground level. The
foundations must be reinforced and construction may proceed with brick force
included between each course in the plinth wall for 6 courses. For the surface bed
preparation, the in situ soils must be removed for 450 mm, and replaced in 150 mm
thick layers with inert material, compacted to a minimum density of 93% of Mod
AASHTO. The allowable bearing pressures not to exceed 50 kPa.
Under individual footings the in situ soils have to be removed to a depth of 1,5 times
the foundation width or to a competent horizon. Excavated material must be
replaced in 150 mm thick layers and compacted to 93% Mod AASHTO density. For
the surface bed preparation, the in situ material must be removed for 450 mm,
replaced in 150 mm layers and compacted to 93% Mod AASHTO density. The
allowable bearing pressures not to exceed 80 kPa.
It is imperative that good site drainage is provided around individual structures and no
excess moisture should accumulate adjacent to foundations.
3.1.2.3.
Zone P (marshy)
Shallow groundwater seepage and the presence of hydrophilic plants indicate a
shallow and permanent perched water table. The soils are loose, silty and clayey
sand, rich in organic matter and of lacustrine origin. It is recommended that no
structures are constructed within this zone, but be developed as open recreational
areas.
3.1.2.4.
Zone P (uncontrolled fill)
A large portion of the south-eastern side of the site was previously used as a
disposal area for ash and domestic waste. The ash is very loose to loose with a
thickness in excess of 2,5 m and significant consolidation can occur.
Structures in this zone must be founded on piles.
3.2.
TRAFFIC IMPACT ASSESSMENT
Sebego Maloka & Viljoen Civil Engineers (Pty) Ltd (SMV) carried out the traffic impact
assessment. The report will be updated taking into account the revised township layout.
3.3.
FLOODLINES
The development is not affected by the flood lines. .
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4.
EXISTING AND PROPOSED SERVICES
4.1.
STORMWATER
4.1.1.
Existing System
A small river runs to the south of the site, in the adjacent development known as
Diepsloot East Ext 0. The whole site, as well as some of the surrounding land,
drains towards it.
There is no existing stormwater system on the site.
4.1.2.
Proposed Stormwater System
It is a requirement of the Johannesburg Roads Agency that the stormwater for all
new developments be attenuated. Provision has been made for one large
attenuation site in the south west corner of the property. In the detail design
phase, the option of attenuation on each individual site will be investigated as
opposed to the one facility.
The attenuation requirement is that the 1 in 20 post-development runoff be
attenuated to be equal to or less than the 1 in 20 year pre-development runoff.
The proposed system will be analysed using the Hydrosim Stormwater Design
Software and Table 2 below lists the relevant design criteria:
TABLE 2 - STORMWATER DESIGN PARAMETERS AND STANDARDS
Design Parameters and Design Standards for Stormwater
Description
Design criteria
Design Flood frequency for minor storms
1:5 Years
Design Flood frequency for major storms
1:25 Years
Maximum encroachment of runoff during minor
storms on class 5b to 5f roads(Residential and low
order roads)
Maximum encroachment of runoff during minor
storms on class 5a roads(Residential access
collectors)
Maximum encroachment of runoff during minor
storms on class 4 roads(Local distributors)
No kerb over-topping,
depth of flow not to exceed 10mm at crown
No kerb over-topping,
flow spread must leave at least 20% of total road
width free of water
No kerbing overtopping
flow spread must leave at least 40% of total road
width free of water
Maximum encroachment of runoff during minor
storms on class 4 roads(Local distributors)
Depth of flow not to exceed 150 mm at crown
Percentage imperviousness
30% except for parks -15%
Infiltration rate
25 mm/h
Final infiltration rate
5 mm/h
Depression storage pervious areas
1 mm
Mean annual precipitation
700 mm
Rainfall distribution
Triangle, time to peak ratio 0,3
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Manning’s n impervious
0,015
Manning’s n pervious
0,25
4.2.
ROADS.
4.2.1.
New External Roads
The specifications for these roads are still to be confirmed by Gautrans
4.2.2.
New Internal Roads
The geometric requirements for the internal roads are listed in Table 3:
TABLE 3 - GEOMETRIC REQUIREMENTS FOR INTERNAL ROADS
Road Reserve
Roadway
Width
Kerb Width
Pavement
Crossfall
20 m
7,2 m
150 mm (Fig 8)
Asphalt
16 m
7m
150 mm (Fig 8)
Asphalt
13 m
6m
150 mm (Fig 8)
Asphalt
10,5 m
6m
150 mm (Fig 8)
Asphalt
3%
Camber
3%
Camber
3%
Crossfall
3%
Crossfall
Parking
4.2.3.
Interlocking
blocks in
herringbone
pattern
Pavement Design
Table 4 below gives the pavement design for the roads
TABLE 4 - ROAD PAVEMENT DESIGNS
Design
Surfacing
Base G1
Subbase C4
Subgrade G7
Roadbed preparation / Subgrade
Description
25 mm thick continuously graded fine grade
asphalt
100/150 mm thick crushed stone compacted to
98 % modified AASHTO density.
150 mm thick G5 gravel stabilised 2 % to C4
material and compacted to 95 % of modified
AASHTO density.
150 mm thick natural gravel compacted to 93
% of modified AASHTO density.
150 mm thick natural gravel compacted to 90
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Fill (where required) G9
% of modified AASHTO.
150 mm thick natural gravel compacted to 90
% of modified AASHTO.
Table 5 below gives the pavement design for the parking areas
TABLE 5 - PARKING AREA PAVEMENT DESIGNS
Design
Surfacing
Subbase C4
Subgrade G7
Roadbed preparation / Subgrade
Fill (where required) G9
4.2.4.
Description
60 mm thick interlocking paving laid in a
herringbone pattern, on 20 mm thick sand
bedding
150 mm thick G5 gravel stabilised 2 % to C4
material and compacted to 95 % of modified
AASHTO density.
150 mm thick natural gravel compacted to 93
% of modified AASHTO density.
150 mm thick natural gravel compacted to 90
% of modified AASHTO.
150 mm thick natural gravel compacted to 90
% of modified AASHTO.
Typical Cross Section
The internal roads will have either a 3 % cross fall or a 3% camber.
4.2.5.
Public transport
Provision is made for public transport within the road layout and geometry.
4.2.6.
Refuse area
Refuse areas will be provided where necessary.
4.2.7.
Sub‐surface drains
To protect the layer works, sub‐surface drains need to be installed where
necessary.
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5.
COST ESTIMATES
5.1.
ROADS
Table 6 below gives the cost estimate for the Roads
TABLE 6 - COST ESTIMATES ROADS
ROADS ESTIMATED COST
Item
No.
Description
1
External Streets
2
Internal Roads
3
Sub Total
4
P&G
5
Sub Total
6
Contingencies
7
8
Sub Total
Value Added Tax (VAT @
14%)
9
TOTAL
5.2.
Unit
Quantity
Rate
Prov
m²
Amount
R 10 000 000.00
30 000.0
R 500.00
R 15 000 000.00
R 25 000 000.00
10.0%
R
2 500 000.00
R 27,500 000.00
10.0%
R
2 750 000.00
R 30 250 000.00
R
14.0%
4 235 000.00
R 34 485 000.00
STORMWATER
Table 7 below gives the cost estimate for the Stormwater
TABLE 7 - COST ESTIMATE STORMWATER
STORMWATER ESTIMATED COST
Item
No.
Description
Unit
1
Stormwater system
m
2
Attenuation Dam
No
3
Other
4
Sub Total
4
P&G
5
Sub Total
6
Contingencies
7
Sub Total
Value Added Tax (VAT @
14%)
10
Quantity
3 000
1
Rate
R 1 500.00
R
1 000 000.00
Prov
Amount
R 4 500 000.00
R 1 000 000.00
R 1 000 000.00
R 6 500 000.00
10.0%
R 650 000.00
R 7,150,000.00
10.0%
R 715 000.00
R 7 865 000.00
14.0%
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R 1 101 100.00
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11
TOTAL
5.3.
R 8 966 100.00
SUMMARY OF COST ESTIMATES
Table 8 below gives the Summary of the Cost Estimates
TABLE 8 - SUMMARY OF COST ESTIMATES
SUMMARY OF ESTIMATED COSTS
Item
No.
Description
Unit
Quantity
Rate
Amount
1
Roads
R 34 485 000.00
2
Stormwater
R 8 966 100.00
3
TOTAL
R 43 451 100.00
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6.
BULK SERVICE CONTRIBUTIONS
JRA would not provide Bulk Service Contributions at this stage. However they did
provide a spreadsheet which is used to calculate the contributions, and this was
utilised. It must be emphasized that these calculations are estimates only, and
are subject to the correct calculation from the utilities.
6.1.
ROADS AND STORMWATER
Contribution
=
No of Parking Bays * R648,08/bay
This rate is from 1 September 2007, so should be escalated at 10% pa.
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