Detailed Design of the Midrand K109 Road
DETAILED DESIGN OF THE MIDRAND K109 ROAD Site Geotechnical Investigations Report: Detailed Design of the Midrand K109 Road Located Between K27 and Dale Roads, Midrand Area, Gauteng Province
Prepared by RoadLab (Pty) Limited For:
Aphane Consulting
On Behalf of: Gauteng Provincial Government: Department of Public Transport, Roads and Works
(Effective Date: 12 December 2014)
RoadLab (Pty) Limited DOCUMENT INFORMATION
Author (s): Kelvin Chimanya Associate Consultant: Eng Geology BSc (Honours), SACNASP Nico Herbst Senior Principal / Director
Date: 12 December 2014
Project Number: APHA01
Print Date: Friday, 12 September 2014
Copies: Aphane Consulting (2) RoadLab (Pty) Limited (1)
Document Change Control
Version Description (section(s) amended) Author(s) Date 1.0 Final report Kelvin Chimanya 08-12-2014 2.0 Peer review Nico Herbst 10-12-2014
Document Review and Sign Off:
Primary Author Peer Review Kelvin Chimanya Nico Herbst
Detailed Design of the Midrand K109 Road Project Site Geotechnical Investigations Report RoadLab (Pty) Limited DOCUMENT INFORMATION
Table of Contents
EXECUTIVE SUMMARY ...... i 1 INTRODUCTION AND TERMS OF REFERENCE ...... 1 1.1 Project Background ...... 1 1.2 Terms of Reference ...... 1 1.3 Scope of Work ...... 2 1.4 Principal Sources of Information ...... 2 1.5 Legislative Requirements ...... 3 1.6 Participants ...... 3 1.7 Limitations and Declarations ...... 4 2 PROPERTY DESCRIPTION AND LOCATION ...... 5 2.1 Project Description ...... 5 2.2 Location and Access ...... 5 2.3 Physiography ...... 6 2.4 Climate ...... 7 2.5 Vegetation and Fauna ...... 7 2.6 Topography and Drainage ...... 7 2.7 Weathering Characteristics ...... 8 2.8 Soils ...... 9 2.9 Proposed Land Use ...... 9 2.10 Local Infrastructure & Services ...... 10 2.11 Trafficability ...... 10 3 GEOLOGICAL SETTING...... 11 3.1 Regional Tectonic Setting ...... 11 3.2 Regional Stratigraphy ...... 12 3.3 Project Geology ...... 15 3.4 Structural Geology ...... 15 4 FIELD OPERATIONAL METHODOLOGY ...... 17 4.1 Desktop Review ...... 17 4.2 Testing Procedures and Equipment Used ...... 17 4.3 Dynamic Cone Penetration Testing ...... 21 4.4 Rock Exposures ...... 21 4.5 Field Parameter Characterisation ...... 21 4.5.1 Residual Soil ...... 21 4.5.2 Transported Soil ...... 22 4.5.3 Pedogenic Material ...... 22 4.6 Key Geotechnical Constraints ...... 23 5 LABORATORY TESTING AND ANALAYSIS ...... 25
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5.1 General Overview ...... 25 5.2 Test Pitting & Profiling Results ...... 25 5.3 Analytical Test Results ...... 27 5.4 Dynamic Cone Penetration Test Survey ...... 34 6 ENGINEERING AND GEOTECHNICAL APPRAISAL ...... 35 6.1 General Overview ...... 35 6.2 Geological Characteristics ...... 35 6.3 Geotechnical Appraisal ...... 36 6.4 Project Geotechnical Characteristics ...... 37 6.4.1 Undifferentiated Transported Soil ...... 37 6.4.2 Hillwash ...... 37 6.4.3 Alluvium ...... 37 6.4.4 Pebble Marker ...... 37 6.4.5 Residual Soil ...... 38 6.4.6 Weathered Granite ...... 38 6.4.7 Granite ...... 38 6.5 Probable Impact on Road Design & Construction ...... 38 6.5.1 Collapsible Soils ...... 38 6.5.2 Expansive Soils ...... 39 6.5.3 Soft Clays ...... 39 6.5.4 Dispersive Soils ...... 39 6.5.5 Pedogenic Materials ...... 40 6.5.6 Slope Instability ...... 40 6.6 Hydrogeology ...... 40 6.7 Structural Foundations & Sidewall Stability ...... 41 7 INTERPRETATIONS AND DESIGN RECOMMENDATIONS ...... 42 7.1 Site Preparation ...... 42 7.2 Earth Works ...... 42 7.3 Geotechnical Recommendations ...... 42 8 CONCLUSIONS ...... 44
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List of Tables
Table 2.7_1 – Weathering characteristics influenced by climate 9 Table 3.2_1 – Regional Stratigraphic Succession of the Midrand Area 14 Table 4.2_1 – Summary of the Geotechnical Test Pits 19 Table 4.4_1 – Weathering characteristics influenced by climate 21 Table 4.5_1 – Probable Origin of Residual Soils in the Project Area 22 Table 4.5_1 – Probable Origin of Transported Soils in the Project Area 22 Table 5.3_1 – Summary of Laboratory Results 33 Table 6.2_1 – Probable Origin of Residual Soils in the Project Area 35 Table 6.3_1 – Key Geotechnical Constraints 36
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List of Figures and Plates
Figure 2.2_1 – General Location of the Midrand K109 Road Project 6 Figure 3.2_1 – Location of Major Cratons and Fold Belts in Southern Africa 11 Figure 3.2_1 – Regional Geology of the Johannesburg Dome 13 Figure 3.2_1 – Geological Map of the Midrand-Centurion Area 16 Figure 4.2_1 – K109 Midrand Project: Location of Geotechnical Test Pits 20 Figure 5.2_1 – Midrand K109 Road Project : Typical Soil Profile 26 Figure 5.3_1 – Midrand K109 Road Design : Typical DCP Survey 28 Figure 5.4_1 – Midrand K109 Road Design : Typical DCP Survey 34 Appendix A_1 – Drawing GRP02/21/1Ply: Sheet 1 of 8 2 Appendix A_2 – Drawing GRP02/21/2Ply: Sheet 2 of 8 3 Appendix A_3 – Drawing GRP02/21/1Ply: Drawing GRP02/21/3Ply: Sheet 3 of 8 4 Appendix A_4 – Drawing GRP02/21/3Ply: Sheet 3 of 8 1
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List of Appendices
Appendix A1–Midrand K109 Project -
Detailed Design of the Midrand K109 Road Project Site Geotechnical Investigations Report: 12 December 2014 RoadLab (Pty) Limited
EXECUTIVE SUMMARY
RoadLab Pty Limited (RoadLab) has been engaged by the Aphane Consulting CC to conduct site geotechnical services during the detailed road design programme of the K109 Road.
This report contains the results of a site geotechnical investigation for the proposed road upgrade, as carried out by RoadLab. The K109 Road lies between the Dale and K59 roads and is located within the Midrand area and truncates through both Johannesburg and Ekurhuleni Metropolitan Cities.
The K109 Road is a greenfields road project and its detailed design will concentrate on following a roughly horizontal alignment to an earlier proposed road design. The vertical alignment will involve approximately cuts and fills measuring 5.2m and 3.5m (respectively). This route is defined by an undulating terrain truncating through a local watershed of the Midrand Area.
The field exploratory work comprised of field visits (site walk-overs), detailed soundings at 59 Direct Cone Penetration (DCP) stations, excavations and sampling from 48 test pits spaced at 100m centres to cover both sides of the route. Due to the extreme variability of the sub soil conditions, extensive laboratory test works were performed on the collected samples.
The area earmarked for the K109 road construction lies within the Glen Austin Agricultural Holdings (AH) of the Midrand Area. The project area is underlain by weathered granites, granodiorites and remnants of mafic and ultra-mafic intrusives assigned to the Halfway House Granite suite of the Basement Complex. Locally, the residual, reworked granites are intensely to moderately weathered and often associated with a thin colluvium sandy gravel and a thick sandy hillwash. The near surface hill wash is a low density, partly saturated soil of significant collapse potential whilst some of the weathered granites have produced clay-rich, loamy soil having significant plasticity and are often of medium swelling/shrinkage potential. Most of the soils sitting on top of the weathered granites are ranked between G5 to G10 (under the COLTO materials classification system).
In shallow cuts or where the road levels are close to the natural ground, the pavement can be subjected to swell movements of the order of 20-30mm or collapse settlements of similar magnitude except under the embankments where these can increase to levels of between 50- 100mm. Most of these movements can be differential because of the non-uniform nature of the problem soils. In addition, the potentially collapsible hillwash should be typified either with heavy vibratory rollers when thin or impact roller.
Appropriate surface and subsurface drainages will be required (especially in the cut areas) in order to prevent the development of perched water tables existing under the road. Cut slopes require protection due to the presence of the highly erodible micaceous granites. Strict geotechnical supervision will be required during the construction phase.
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1 INTRODUCTION AND TERMS OF REFERENCE
1.1 Project Background
RoadLab was engaged by Aphane Consulting (Pty) Limited to offer site geotechnical consultancy during the design of the proposed K109 Road located between Dale Road and the K59. The proposed K109 road is a greenfields project aimed at improving the trafficability of vehicles within the region.
The function of K-routes is two-fold, namely to serve through traffic (i.e., traffic having neither an origin nor a destination in the area traversed by them), as well as to provide area access from the higher order freeway system to the surrounding land. Freeways (PWV-routes) are usually spaced at an 8km to 12km grid, while major arterials (K-routes) are spaced at approximately 1.8km to 2.4km intervals. Minor arterials and collector roads are again linked to the K-routes at 600m or larger intervals to complete the higher order road network. The K109 is part of the second order mobility network planned for the Gauteng Province. It would also provide local accessibility by means of well-spaced intersections with minor arterials and collector roads and in a few instances give direct access to minor tracts of land. The proposed activity is the detailed design and construction of the proposed K109, including all required access roads.
The site geotechnical investigations conducted by RoadLab would ascertain the sub- surface conditions available at the proposed road construction site and provide recommendations regarding founding depths for the new structure.
1.2 Terms of Reference
RoadLab has been commissioned to carry out the following activities in the geotechnical investigations required to aid the detailed design of the proposed K109 road within the Glen Austin Area of Midrand:-
. Evaluation of the geology and hydrogeology of the site.
. To establish the subsoil conditions prevailing within the project area.
. Examination of existing geotechnical information pertaining to the site.
. Supervision of the site excavations or boring in soil or rock and conduct a systematic logging programme.
. Field assessment of geotechnical properties of materials.
. Evaluation of geotechnical properties of tested soils.
. Submit appropriate data and recommendations that would aid the effective design of the proposed road outline.
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1.3 Scope of Work
RoadLab was requested by Aphane to conduct a site geotechnical survey of the project site. The aim of the survey was to establish the general geotechnical characteristics of the area and define key geotechnical constraints for the project. Based on the information supplied by Aphane, the site geotechnical investigations will include the following project aspects:-
. A desktop review to determine previous land uses and obtain general overview of the expected soils, geology and hydrogeological conditions at the site. . Conducting site inspections (limited to publicly accessible areas of the site). . Reconnaissance site visits. . On site field supervision during excavations of trial holes by use of a Tractor- Loader-Backhoe (TLB). . To quantify and qualify the nature of the engineering properties of the underlying soil and rock strata for the proposed road site. . To evaluate the geotechnical characteristics of the proposed site. . To identify possible fatal flaws in the geotechnical characteristics of the site . To provide sound technical recommendations for the development of the proposed road site. . Foundation Indicator tests (including Grading; Atternberg Limits and Hydrometer) . Analyses to determine the engineering characteristics of the unconsolidated materials. . MOD AASHTO density and CBR strength tests to determine efficacy of these materials for road construction and/ or platforms at the site. . Dynamic Cone Penetration (DCP) tests done at the base of and/ or adjacent to the trial holes to enable calculation of bearing capacity in unconsolidated materials. . Quality/density measurements of in-situ materials.
. Provide an Independent Technical Report encompassing the results from the site geotechnical investigations (with solutions and conclusions where applicable).
1.4 Principal Sources of Information
Data and information required to complete the site geotechnical investigations were obtained by RoadLab from the client and/or other geoscientific data available from the public domain. These data and information are summarised as follows:
. 1:50,000: Topographic map of the Centurion area (Sheet 2526CC).
. 1:50,000: Geological map of the Centurion area (Sheet 2526CC).
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. Drawing GRP02/21/1Ply: Sheet 1 of 8-Preliminary Design of the K109 Road from Kaalfontein to K54, Layout and Services Plan from Stations 3.1 to 4.7km (1:1,000).
. Drawing GRP02/21/2Ply: Sheet 2 of 8-Preliminary Design of the K109 Road from Kaalfontein to K54-Layout and Services Plan from Stations 4.0 to 5.7km (1:1,000).
. Drawing GRP02/21/3Ply: Sheet 3 of 8-Preliminary Design of the K109 Road from Kaalfontein to K54-Layout and Services Plan from Stations 5.7 to 7.4km (1:1,000).
. Drawing GRP02/21/4Ply: Sheet 4 of 8-Preliminary Design of the K109 Road from Kaalfontein to K54-Layout and Services Plan from Stations 7.4 to 9.1km (1:1,000). .
1.5 Legislative Requirements
The scope of work for this site geotechnical investigations survey has been performed in general accordance with requirements outlined in the following documents:-
. The National Environmental Management Act, 1998 (Act No. 107 of 1998) . The National Water Act, 1998 (Act No. 36 of 1998) . The National Heritage Resources Act, 1999 (Act No. 25 of 1999). . National Road Traffic Act, 1996 (Act No. 93 of 1996) . Mine Health and Safety Act, 1996 (Act 29 of 1996) . Environmental Impact Assessment Regulations . Environmental Conservation Act, 1989 (Act No. 73 of 1989) . SAICE: Site Geotechnical Investigations Code of Practice . SANS 634: Geotechnical Investigations for Township Development.
1.6 Participants
The project participants consist of technical experts engaged by RoadLab Limited and tasked with conducting a detailed geotechnical review of the project area. The key participants on the project with their individual areas of responsibility are listed below:-
Kelvin Chimanya (Associate Geology Consultant): RoadLab Limited BSc (Honours), Pr.Sci.Nat, . Technical supervision (geology review, geotechnical interpretations, audits, etc)
. Geographical Information Systems (GIS)
. Database management
. Quality control and quality assurance (QA/QC)
. Technical report (primary author).
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Julien (Field Technician): RoadLab Limited
. Budgetary control
. Logistical coordination
. Safety, health and community-relations (SHEC)
Linda van Niekerk (Lab Technician): RoadLab Limited
. Lab results reporting
Nico Herbst (Operations Director): RoadLab Limited
. Project management
. Technical report (peer review)
1.7 Limitations and Declarations
The author of this report has inspected and verified the locality of the Project site and has been involved in the on-site design and implementation of the site geotechnical activities, the processing and interpretation of data and also in the preparation of this report. RoadLab Limited has not reviewed the property ownership of the individual farms and has not independently verified the legal status or ownership of the built and installed properties. RoadLab has prepared this site geotechnical report (the "Report") for the exclusive use of Aphane Consulting (Pty) Limited (the "Client"); the Gauteng Provincial Government Department of Public Transport, Roads and Works (“GAUTRANS”); Regulatory Authorities; Auditors and others approved by the Client for the purpose of the Site Geotechnical Investigations to aid the detailed design of the Midrand K109 construction project in the Glen Austin Area of Midrand.
Neither RoadLab nor the authors of this report have any financial interest in Aphane Consulting or the Project. This report has been prepared solely on the basis of professional fees received from the client. In addition, RoadLab has exercised all due care in the preparation of the Report and believes that the information, conclusions, interpretations and recommendations of the Report are both reasonable and reliable.
RoadLab makes no warranty or representation to the Client or third parties (express or implied) in respect of the Report, particularly with regards to any commercial investment decision made on the basis of the Report. Use of the Report by the Client or third parties shall be at their own risk and extracts from the Report may only be published with permission of RoadLab. This document has been prepared for the exclusive use by Aphane Consulting (the “Client”) and its associates, on the basis of instructions, information and data supplied by the Client.
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2 PROPERTY DESCRIPTION AND LOCATION
2.1 Project Description
Midrand is strategically located approximately 25km north of the Johannesburg CBD and approximately 28km south of the Pretoria CBD. Midrand is 240km2 and stretches from the Allandale Interchange in the south to the Olifantsfontein Interchange in the north and from Kyalami in the west to Tembisa in the east. Midrand is divided into an east and west area by the N1 Highway which runs through the centre of Midrand. Midrand is divided into eight functional zones characterised by different land use patterns as follows:-
. Zone 1: Bluehills and Diepsloot. . Zone 2: Kyalami, Barbeque and Crowthorn. . Zone 3: Erand, Vorna Valley and Waterval. . Zone 4: Noordwyk and Country View. . Zone 5: Central Activity District . Zone 6: Randjesfontein, Glen Austin and Presidential Park . Zone 7: Olifantsfontein and Clayville . Zone 8: Ivory Park, Rabie Ridge and Commercial
2.2 Location and Access
The site earmarked for the K109 Road construction project is situated in the Zone 6 of the Midrand Area and truncates the area located between the Rantjesfontein and Oliphantsfontein Farms (Farm Numbers 405JR and 410JR, respectively). The project site is under the jurisdiction of both the Johannesburg and the Ekurhuleni Metropolitan cities. The general location of the project site is shown in Figure 2.2.
Amongst the notable localities include the Midrand Gautrain Station (west-southwest), (Grand Central Aerodrome (west-southwest), Ivory Park (south-southeast), the Glen Austin Agricultural Holdings (west), President Park Agricultural Holdings (south) and the Olifantsfontein Farm (east). The Randjesfontein Agricultural Holdings and the Olifantspruit Boanste Dam occur to the northwest and east-northeast (respectively).
The Midrand Licensing Department is located south of the proposed route whilst the Glen Austin Pan has been placed just west of the proposed route near its southern extreme point where it enters Dale Road. The K109 Road Construction Programme is a typical “Greenfields Project” located within the Glen Austin Agricultural Holdings (AH). The Glen Austin AH is a small-holdings farming area of Midrand. The proposed route has no major existing infrastructure other than an existing gravel road that truncates against the old Oliphantsfontein Road. Access to the project site is via the N1 Highway and off-ramping onto the New Road and heading towards the K101. Easy access is either via the Dale Road or the Oliphantsfontein Road.
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Figure 2.2_1 General Location of the Midrand K109 Road Project
2.3 Physiography
The present land surface in the Johannesburg area was defined by the effects of the African and Post-African (levels I & II) geomorphic cycles. The African Cycle was initiated by a vertical uplift during the Late Jurassic to Early Cretaceous and lasted for more than 100Ma. The African Cycle caused the development of residual soil, extensive kaolinisation and the widespread development of pedocretes and around the Johannesburg Dome region is represented by hill crests with elevation of above 1600m amsl. The Post-African I (Early Miocene) cycle was initiated by an uplift of 150m to 300m and was accompanied by a slight westward tilting and was accompanied by considerably deep residual soils developing in the humid areas. In the Johannesburg Dome region, this erosional cycle is represented by areas with 1400-1600m amsl. The Post-African II (Late Pliocene) cycle was initiated by a major asymmetrical uplift of the subcontinent occurring with a major westward tilting of the land surfaces of the interior and monoclinal warping along the southern and eastern coastal margins. This event had also caused the formation of the erosional surface characterised by the incision of coastal gorges and the down-cutting and formation of higher terraces along interior rivers. The Post African II erosion surface is generally manifested in areas located below 1500m amsl.
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2.4 Climate
The Midrand area has a warm and moderate climate characterised by hot summers and mild winters. Rainfall occurs predominantly in the summer with little rainfall recorded in winter. The rainfall occurs mainly in the form of thundershowers.
The climate of the Midrand area is typical of the Highveld region. The average annual rainfall is estimated around 710 mm. The wettest month of the year is around January (with an average monthly total rainfall of 125 mm) and the driest month is July (with an average monthly total rainfall of 4 mm). Winds are mostly north-westerly with an average speed of 3 m/s. The windiest months are recorded during September to December. A mean annual precipitation and temperature (600-800mm and 17.5-20.0°C, respectively) suggests moderate decomposition of the bedrock should be expected.
2.5 Vegetation and Fauna
The characteristic vegetation type found in Midrand is typical Highveld grassland. The indigenous vegetation consists mainly of themeda-triandra, trystachya-leucothrix, trachypon-spicatus and elionurus-meticus. Within the Glen Austin area, the main vegetation characteristics are the Savanna-Biome, the Bushveld Basin with Egoli grassland being more prevalent. However, within the project area, over 95% of the land has already been transformed. The Midrand area is also rich in cultural, historical and archaeological sites, with around 51 sites being recorded in the area.
The Glen Austin Bird Sanctuary (reckoned to be about 3.5 million years old) includes pans and associated terrestrial habitat with an ecosystem spanning an area of 500 hectares. The Bird Sanctuary (proclaimed a nature reserve in 1994) is home to many different species of birds and mammal including the Giant African Bullfrog (Pyxiecephalus Adspersus Tschudi). Other bird species include the fish eagle, secretary bird, Flamingos, Purple Gallinule, Hamerkop, Herons, Grey Hornbill, paradise fly catcher, Barn Owl, etc. Currently, there are 3 threatened or endemic plant and animal species including the Giant Bullfrog, the Marsh sylph/Egoli granite grassland and; the water pans (Olifantspruit, Glen Austin and Sedge). RoadLab is not aware of any environmental liabilities associated with the K109 Road Construction Project.
2.6 Topography and Drainage
The overall project area is defined by gentle to moderate slopes ranging from 2-7°. The average ground elevation ranges from a minimum of 1520m to roughly around 1620m above mean sea level (northern and southern end respectively). Three main river systems form part of the Midrand municipality; Kaalspruit/Olifantspruit, Rietspruit and Juskei River.
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The main drainage system of the project area is defined by the Olifantspruit Stream, a perennial river flowing roughly parallel to the proposed route and intersection the proposed K109 near the intersection with the K562 Road. Most of the perennial streams pour their water into the Olifantspruit-Boanste Dam.
The streams draining the area to the south of the proposed road drain into the Kaalspruit River. Near the south of the proposed route lie the Glen Austin and the Sedge water pans. Drainage patters within the project area appear to be structurally-controlled with drainage features consisting of a number of small streams flowing northwards (northern portion of the study area) and south-westerly (southern portion of the area).
2.7 Weathering Characteristics
Weathering is the process of alteration and breakdown of rock and soil materials at and near the Earth’s surface by chemical decomposition and physical. Rock masses are frequently weathered near ground level, and are sometimes altered by hydrothermal processes. The weathering (and alteration) is generally more pronounced on the rock exposed on the discontinuity surfaces than in the interior of rock blocks because water flow occurs in the discontinuities. These results in the rock strength on the discontinuity surfaces being less than that of the fresher rock found in the interior of the rock blocks.
There are two main results of weathering; one dominated by mechanical disintegration, the other by chemical decomposition including solution. Generally, both mechanical and chemical effects act together, but, depending on climatic regime, one or other may be dominant. Mechanical weathering results in opening of discontinuities by rock fracture, the opening of grain boundaries, and the fracture or cleavage of individual mineral grains. Chemical weathering results in discoloration of the rock and leads to the eventual decomposition of silicate minerals to clay minerals; some minerals, notably quartz, resist this action and may survive unchanged. Solution is an aspect of chemical weathering, which is particularly important in the case of carbonate and saline minerals.
According to Weinert (1980), chemical weathering (decomposition) predominates in areas having the N-value of 2-5 whilst physical weathering predominates in areas with the N-value higher than 5. Within the project site, chemical weathering is prevalent and has led to an establishment of a soil profile characterised by kaolinite and montimorillonite. Weinert values between 2-5 suggests that residual soils will be of average depth, transported soils will be shallow and pedocretes (where present) will be ferruginous (giving rise to calcrete and hardpan material).
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Table 2.7_1 Weathering Characteristics (After Weinert, 1980)
Principle Secondary N-Value Mode of Weathering Weathering Characteristics Minerals Montimorillonite and kaolinite change to Kaolinite, <1 Decomposition sesquioxides; Very deep weathering profiles sesquioxides Montimorillonite changes to kaolinite in top soil Kaolinite, <2 Decomposition layers; Deep weathering profiles montimorillonite Weathering profile deepens towards N=2; Kaolinite, 2-5 Decomposition Significant secondary minerals montimorillonite 5-10 Disintegration Few secondary minerals Hydrous mica, illite >10 Disintegration Thin weathering layer; No secondary minerals. Almost none
2.8 Soils
From an engineering point of view, a soil can be regarded as any uncemented or weakly cemented accumulation of mineral particles formed mainly by the weathering of rocks, with void spaces filled with air and/or water between the particles. The maximum unconfined compressive strength of a soil is 700kPa.
Within the project area, the most prevalent landscape may have been defined by events leading to the Post African I and II erosional cycles. Remnants of kaolinised, leached zones accompanied by broad areas of irregular basal core stone zone are common. Deep weathering may be explained by an advanced hydrolysis of silicate minerals (caused by increased fracturing due to fracturing).
Generally, there seems to be preferential weathering of the bedrock with deep weathering troughs observed in areas north of the project area. Feldspars have become thoroughly kaolinised and leached from the top layers resulting in spongy, micaceous, silty sand. Few core stones are present in the profile, sometimes accompanied by hardpan ferricrete.
The origin of a soil at a specific location can be due to the weathering of in situ rock (residual soil), transportation of materials (transported soils) or it can be man-made (pedogenic materials).
2.9 Proposed Land Use
The proposed alignment of the K109 has been included in the Gauteng Strategic Road Network Review (2010) and is protected in terms of the Gauteng Transport Infrastructure Act, 2001 (Act 8 of 2001).
The Gauteng major roads network is critically evaluated and adapted on a continuous basis (to comply with latest land use and other related investment developments. The route determination for the K109 Road was conducted in the mid-1970. The proposed K109 Road is a physical infrastructure with the following specifications:-
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. It is a national road as defined in Section 40 of the South African National Roads Agency Limited and National Roads Act, 1998 (Act No. 7 of 1998). . It will be a road to be administered by a provincial authority.
. The road reserve is wider than 30 metres (or the road will cater for more than one lane of traffic in both directions).
2.10 Local Infrastructure & Services
During site geotechnical investigations, several intersecting roads were observed in the area. The area is serviced by septic sewer tanks that are being self-managed by the private individuals. A large portion of the project site comprises of small farm sub- holdings that rely heavily on groundwater for their irrigation and domestic needs.
2.11 Trafficability
Generally, the road network of the Midrand area can be divided into four main categories which are; national, provincial, local paved and local gravel/dirt. High levels of traffic congestion are experienced during the early morning and late afternoon peak hours. High volumes of traffic is recorded on the N1 motorway, with substantial volumes of cars recoded at the Midrand interchanges coming from the east (Ivory Park and Tembisa), the west (Diepsloot) and from the southwest of the Midrand area.
When Glen Austin area had experienced excessive through traffic, calming devices has been introduced in the past with the aim of giving horse riders relaxed freedom for riding in the area. Glen Austin is also the home of the well-known Midrand Country Cyclists and it is significant to see how many "city" cyclists escape to the roads in and around Glen Austin during weekends.
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3 GEOLOGICAL SETTING
3.1 Regional Tectonic Setting
The Kaapvaal Craton covers an area of approximately 1,200,000 km2 and is joined to the Zimbabwe Craton (to the north) by the Limpopo Belt. To the south and west, the Kaapvaal Craton is flanked by Proterozoic orogens, and to the east by the Lebombo monocline that contains Jurassic igneous rocks associated with the break-up of Gondwana. The Kaapvaal Craton formed and stabilised between 3.7 and 2.6Ga by the emplacement of major granitoid batholiths that thickened and stabilised the continental crust during the early stages of an arc-related magmatism and sedimentation cycle. The craton is a mixture of early Archean (3.0–3.5Ga) granite greenstone terranes and older tonalitic gneisses (ca. 3.6–3.7Ga), intruded by a variety of granitic plutons (3.3-3.0Ga).
Figure 3.2_1 Major Cratons and Fold Belts of Southern Africa
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3.2 Regional Stratigraphy
The Midrand area is underlain by Archean Cratonic rocks assigned to the Johannesburg Dome (also known as the Halfway House or the Johannesburg-Pretoria Dome). The Johannesburg Dome is a dome-like window of ancient granitoid (approximately 750km2) in area that is situated in the Central part of the Kaapval Craton.
The Archean Johannesburg Dome is located in the central part of the Kaapvaal Craton and consists of trondhjemitic and tonalitic granitic rocks intruded into mafic-ultramafic greenstones. Studies using U-Pb single zircon dating for granitoid samples yield an age of 3340±3Ma and represents the oldest granitoid phase recognised so far. Following the trondhjemite-tonalite gneiss emplacement, a further period of magmatism took place on the dome, which resulted in the intrusion of mafic dykes that are manifest as hornblende- amphibolites. The age of these dykes has yet to be determined quantitatively, but they fall within the time constraints imposed by the age of the trondhjemitic-gneisses (3340– 3200Ma) and later, crosscutting, potassic-granitoids.
The Johannesburg Dome consists of the following:-
. An Archean granitoid dome consisting of Tonalite-Trondjhemite gneisses, banded gneiss, a foliated granodiorite zone and granodiorites. Remnants of greenstone rocks are scattered throughout the Basement inlier. . Rocks assigned to the Witwatersrand and Ventersdorp Supergroups that are exposed along the south-eastern margin, and along the southern and south- western margins of the inlier (respectively). . The Black Reef Formation, which forms the base of the Transvaal Supergroup is exposed to the north-eastern, northern and north-western margin of the inlier and unconformably overlies the granitoids and greenstones as well as the rocks assigned to the Witwatersrand and Ventersdorp supergroups. . The greenstone remnants that occur scattered throughout the Basement inlier are the oldest rocks of the Johannesburg Dome with an age of 3750-2870Ma. They include the mafic and ultramafic rocks (e.g. Muldersdrift and Roodekrans ultramafic complexes) altered to serpentinites, a variety of amphibolites and talc-chlorite- carbonate schists.
. Foliated Granodiorite: Forms a transitional zone between the granodiorites (exposed in the south) and the banded gneiss (exposed in the north).
Detailed Design of the Midrand K109 Road Project Page: 12 Site Geotechnical Investigations Report: 12 December 2014
RoadLab (Pty) Limited
Figure 3.2 Regional Geological Map of the Johannesburg Dome
Detailed Design of the Midrand K109 Road Project Page: 13 Site Geotechnical Investigations Report: 12 December 2014
RoadLab (Pty) Limited
Table 3.2_1 Regional Stratigraphic Succession of the Midrand Area
Supergroup Group Subgroup Formation Code Lithology (Quaternary) (Recent) (Surface Deposits) Unconsolidated sands Undifferentiated Sediments Basalt, dolerite dykes Karoo Ecca Vryheid Pv Sandstone, shale Dwyka C-Pd Diamictite, shale Timeball Hill Vt Shale, siltstone, conglomerate, quartzite Pretoria Hekpoort Vha Volcanic rocks Transvaal Chuniespoort Malmani Vmd Dolomite, chert Black Reef Vbr Quartzite, Shale Platberg R-Vp Breccia, conglomerate, shale Ventersdorp Klipriviersberg Rk Lava, agglomerate, porphyry, tuff Turffontein Rt Quartzite, conglomerate, shale Central Rand Johannesburg Rjo Quartzite, greywacke, conglomerate, lava Jeppestown Rh Shale, quartzite, conglomerate, lava Witwatersrand Government Rg Quartzite, greywacke, conglomerate, lava West Rand Hospital Hill Rh Shale, quartzite, banded ironstone Orange Grove Ro Quartzite, shale, conglomerate Halfway House Granite Z, Zh Granite, gneiss, granodiorite, granitic-gneiss Basement Complex Zm Mafic and ultramafic rocks
Mulungwa Coal Project – JMUL02 Page: 14 KCM Field Operational Report – 12 December 2014
3.3 Project Geology
Generally, within the Midrand area, a total of four different lithological assemblages have been recognised as follows:-
. Banded Gneiss: Outcrop in the northern half of the granitoid inlier and consist of gneisses with a strong banding defined by alternating layers of quartz-feldspar and biotite. . Foliated Granodiorite: Forms a transitional zone between the granodiorites (exposed in the south) and the banded gneiss (exposed in the north). . Granodiorite: This rock exhibits weakly-developed gneissic foliation.
. Granite:
. Mafic and ultramafic remnants: Locally, greenstone remnants that occur scattered throughout the Basement inlier were observed and appear locally altered to serpentinites, amphibolites and talc-chlorite schists.
According to the published geological map of the area, the project site is underlain at depth by weathered granitic rocks assigned to the Halfway House Granite Formation. Locally, this formation is truncated by dolerite intrusive dykes trending northeast-southwest and northwest- southeast. Within the project site, the main lithologies include granite, granodiorite and minor gneiss. No areas with carbonate cover were observed.
3.4 Structural Geology
Ductile shear zones are common within the granitoids of the Basement inlier. These shear zones are characterised by mylonitic foliation and extensive quartz veining. The shear zones were reactivated as brittle faults after the deposition of the Black Reef Formation. It is thus common to observe weathering resistance caused by the extensive quartz veining associated with shear zones and/or mylonite.
A total of five sets of structural features have been identified regionally over the Johannesburg Dome. The most prominent one are the north-south, northeast-southwest and the north- northwest/south-southeast trending features. The prominent Glen Austin Fracture Zone (GAFZ) is a possible major controlling structural feature of the Johannesburg Dome. It is a possible half- graben structure with a downthrow to the south.
Detailed Design of the Midrand K109 Road Page 15 Geotechnical Investigations Report – September 2014
Figure 3.2_1 Geological Map of the Midrand-Centurion Area Adapted from the Geological Map of the Centurion Area (Sheet 2526CC) - 1:50,000
Detailed Design of the Midrand K109 Road Project Page: 16 Site Geotechnical Investigations Report
4 FIELD OPERATIONAL METHODOLOGY
4.1 Desktop Review
A desktop review was implemented to evaluate current and previous land uses and implications for environmental contamination, hydrology and geology. The desktop review was performed with the aimed of identifying potential shortcomings in data coverage.
. Assessment of Google images for the Glen Austin and surrounding areas. . Interim review of soil, geology and hydrogeology conditions (including survey, mapping and other baseline data sourced from the public domain for data.
. Summary review of some of the previous geotechnical reports conducted in the Midrand Area. 4.2 Testing Procedures and Equipment Used
The fieldwork for the site geotechnical investigation was carried out in two parts:-
. Reconnaissance Survey: The site reconnaissance survey was conducted from the 16th to the 20th August 2014 and included a preliminary site walk-over of the project site. This fieldwork had also involved pit excavations, soil profiling/logging, pit sampling, and pit surface reinstatement. A total of 12 test pits were excavated and subsequently backfilled with the assistance of a hired Cat 424D Tractor Loaded Backacter (TLB). All the test pits were excavated within spacing of 500m and to a targeted depth of 1.5m below existing. The total cumulative depth for the excavations was 16.80m and ranged from 0.60m to 2.50m. In addition, a total of 4 historical test pits were recorded on site near the vicinity of the Glen Austin water pan. The original stations of the trial holes was spaced within 500m centres, later reduced to 400m and further reduced to 100m near the Glen Austin water pan. Each of the trial holes was profiled in detail and representative soil samples recovered for laboratory testing purposes.
. Main Site Geotechnical Survey: From the 7th to 10th October 2014, a detailed site visit of the project area was conducted by the Roadlab Team. This fieldwork involved conducting pit excavations at 36 pre-designed stations, soil profiling/logging, pit sampling, and pit surface reinstatement. All the test pits were excavated within a spacing of 100m, to a targeted depth of 1.5m below existing ground surface. All excavated test pits were subsequently backfilled with the assistance of a hired Cat 424D Tractor Loaded Backacter (TLB). The total cumulative depth for the excavations was 66.90m and ranged from 0.165m to 2.75m in depth. Each of the trial holes was logged in great detail and representative soil samples recovered for laboratory testing purposes.
Detailed Design of the Midrand K109 Road Page 17 Site Geotechnical Investigations Report
Table 4.2_1 Summary of the Geotechnical Test Pits
Test Station Wheel Final Pit DCP DCP Testing ID Date Easting Northing RL Comments Pit (km) Path Depth Width Locality Depth Programme 1 16-08-2014 TP1 - - 617546 7129525 1530 1.750 0.75 DCP01 0.893 Reconnaissance Survey - 2 19-08-2014 TP2 - - 617432 7129043 1540 1.500 0.75 DCP03 1.004 Reconnaissance Survey - 3 19-08-2014 TP3 - - 617342 7128625 1555 1.500 0.75 DCP05 1.020 Reconnaissance Survey - 4 19-08-2014 TP4 - - 617251 7128239 1560 1.500 0.75 DCP07 0.943 Reconnaissance Survey - 5 19-08-2014 TP5 - - 617167 7127846 1567 0.850 0.75 DCP09 0.807 Reconnaissance Survey - 6 19-08-2014 TP6 - - 617069 7127447 1577 1.500 0.75 DCP11 1.010 Reconnaissance Survey - 7 19-08-2014 TP7 - - 616972 7127060 1588 1.500 0.75 DCP13 0.971 Reconnaissance Survey - 8 19-08-2014 TP8 - - 616897 7126675 1598 1.500 0.75 DCP15 0.972 Reconnaissance Survey - 9 20-08-2014 TP9 - - 617008 7126541 1594 2.500 0.75 DCP17 0.990 Reconnaissance Survey - 10 20-08-2014 TP10 - - 616995 7126344 1594 0.850 0.75 DCP19 0.997 Reconnaissance Survey - 11 20-08-2014 TP11 - - 616952 7126210 1598 1.250 0.75 DCP21 0.998 Reconnaissance Survey - 12 20-08-2014 TP12 - - 616868 7126117 1592 0.600 0.75 DCP23 0.347 Reconnaissance Survey - 13 07-10-2014 TP13 3.900 LCENT 616858 7126113 1601 0.950 0.75 DCP24 0.849 Main Survey - 14 07-10-2014 TP14 4.000 RRHS 616953 7126153 1600 2.225 0.75 DCP25 1.158 Main Survey - 15 07-10-2014 TP15 4.100 LLHS 617009 7126240 1600 2.050 0.75 DCP26 1.036 Main Survey - 16 07-10-2014 TP16 4.200 RCEN 617098 7126292 1599 2.450 0.75 DCP27 1.131 Main Survey - 17 07-10-2014 TP17 4.300 LRHS 617148 7126382 1601 2.450 0.75 DCP28 1.140 Main Survey - 18 07-10-2014 TP18 4.400 RLHS 617227 7126451 1602 2.000 0.75 DCP29 0.295 Main Survey - 19 07-10-2014 TP19 4.500 LCENT 617263 7126545 1602 2.250 0.75 DCP30 1.153 Main Survey - 20 07-10-2014 TP20 4.600 RRHS 617295 7126614 1603 2.400 0.75 DCP31 1.163 Main Survey Homestead 21 07-10-2014 TP21 4.700 LLHS 617356 7126724 1600 2.750 0.75 DCP32 1.170 Main Survey - 22 07-10-2014 TP22 4.800 RCEN 617418 7126805 1603 2.150 0.75 DCP33 1.157 Main Survey - 23 07-10-2014 TP23 4.900 LRHS 617427 7126909 1597 2.050 0.75 DCP34 0.517 Main Survey - 24 08-10-2014 TP24 5.000 RLHS 617471 7127001 1593 2.600 0.75 DCP35 1.120 Main Survey - 25 08-10-2014 TP25 5.100 LCENT 617470 7127103 1587 2.450 0.75 DCP36 0.795 Main Survey - 26 08-10-2014 TP26 5.200 RRHS 617518 7127195 1582 1.950 0.75 DCP37 0.350 Main Survey - 27 08-10-2014 TP27 5.300 LLHS 617511 7127299 1577 0.200 0.75 DCP38 0.310 Main Survey TLB refusal 28 08-10-2014 TP28 5.400 RCEN 617559 7127391 1573 2.650 0.75 DCP39 0.353 Main Survey - 29 08-10-2014 TP29 5.500 LRHS 617558 7127495 1567 2.200 0.75 DCP40 0.540 Main Survey - 30 08-10-2014 TP30 5.600 RLHS 617601 7127588 1563 0.600 0.75 DCP41 0.490 Main Survey TLB refusal 31 08-10-2014 TP31 5.700 LCENT 617606 7127686 1559 1.950 0.75 DCP42 0.700 Main Survey - 32 08-10-2014 TP32 5.800 RRHS 617633 7127778 1554 0.900 0.75 DCP43 0.599 Main Survey - 33 08-10-2014 TP33 5.900 LLHS 617656 7127878 1551 0.750 0.75 DCP44 0.755 Main Survey TLB refusal 34 08-10-2014 TP34 6.000 RCEN 617680 7127980 1547 0.400 0.75 DCP45 0.482 Main Survey TLB refusal
Detailed Design of the Midrand K109 Road Page 18 Site Geotechnical Investigations Report
Table 4.2_1 Summary of the Geotechnical Test Pits
Test Wheel DCP DCP Testing ID Date Station Easting Northing RL Depth Width Comments Pit Path Locality Depth Programme 35 08-10-2014 TP35 6.100 LRHS 617700 7128075 1543 0.950 0.75 DCP46 0.540 Main Survey TLB refusal 36 08-10-2014 TP36 6.200 RLHS 617726 7128179 1540 2.200 0.75 DCP47 1.090 Main Survey - 37 08-10-2014 TP37 6.300 LCENT 617742 7128268 1538 0.165 0.75 DCP48 0.895 Main Survey - 38 09-10-2014 TP38 6.400 RRHS 617770 7128373 1536 1.350 0.75 DCP49 1.040 Main Survey - 39 09-10-2014 TP39 6.500 LLHS 617783 7128463 1533 2.650 0.75 DCP50 0.465 Main Survey - 40 09-10-2014 TP40 6.600 RCEN 617814 7128564 1531 1.800 0.75 DCP51 1.095 Main Survey - 41 09-10-2014 TP41 6.700 LRHS 617833 7128673 1528 2.450 0.75 DCP52 1.100 Main Survey - 42 09-10-2014 TP42 6.800 RLHS 617871 7128750 1524 2.300 0.75 DCP53 1.105 Main Survey - 43 09-10-2014 TP43 6.900 LCENT 617878 7128855 1519 2.500 0.75 DCP54 1.115 Main Survey - 44 09-10-2014 TP44 7.000 RRHS 617920 7128948 1518 1.800 0.75 DCP55 1.100 Main Survey - 45 09-10-2014 TP45 7.100 LLHS 617942 7129075 1520 1.650 0.75 DCP56 0.255 Main Survey - 46 09-10-2014 TP46 7.200 RCEN 617972 7129150 1521 2.250 0.75 DCP57 0.305 Main Survey - 47 09-10-2014 TP47 7.300 LRHS 617969 7129255 1523 2.250 0.75 DCP58 1.085 Main Survey - 48 09-10-2014 TP48 7.400 RLHS 618010 7129348 1519 2.300 0.75 DCP59 1.090 Main Survey - - - OTP1 - - 616899 7126564 1596 2.200 0.75 - - Historical Survey - - - OTP2 - - 616916 7126401 1590 0.800 0.75 - - Historical Survey - - - OTP3 - - 616864 7126262 1584 1.000 0.75 - - Historical Survey - - - OTP4 - - 616825 7126132 1595 0.600 0.75 - - Historical Survey -
LCENT = Left Wheel Path, Centre Position RRHS= Right Wheel Path, Right Hand Side Position RCENT = Right Wheel Path, Centre Position LRHS = Left Wheel Path, Centre Position RHS = Right Wheel Path, Right Hand Side Position TP = Test Pit OTP = Old Test Pit
Detailed Design of K109 Road Page 19 Site Geotechnical Investigations Report
Figure 4.2_1 K109 Midrand Project: Location of Geotechnical Test Pits
Detailed Design of the Midrand K109 Road Project Page: 20 Site Geotechnical Investigations Report
4.3 Dynamic Cone Penetration Testing
Dynamic Cone Penetrometer (DCP) tests were conducted with the aim of calculating of the bearing capacity in unconsolidated materials and use the results to classify in-situ road, sub- grade materials (TRH4). DCP tests were carried out to a depth of 1.0m at 200m and 100m spaced intervals (reconnaissance and main survey programmes, respectively). A total of 59 DCP stations were tested with a one-meter instrument (23 sounding stations during the reconnaissance phase and 36 stations during the main survey). Results of the DCP tests are shown in the Appendix.
4.4 Rock Exposures
Rock exposures were encountered at two localities situated near the Glen Austin water pan. Detailed rock descriptions are indicated in the Appendix to this report.
Table 4.4_1
Rock Mas Weathering
Term Description Grade Abbreviation Unweathered/ No visible sign of rock material weathering; perhaps slight I UW Fresh discoloration on major discontinuity surfaces Slightly Discoloration indicates weathering of rock material and discontinuity SW Decomposed/ surfaces. All the rock material may be discoloured by weathering II Weathered and may be somewhat weaker externally than in its fresh condition. Moderately Less than half of the rock material is decomposed and/or MW Decomposed/ disintegrated to a soil. Fresh or discoloured rock is present either as III
Weathered a continuous framework or as corestones. Highly More than half of the rock material is decomposed and/or Decomposed/ disintegrated to a soil. Fresh or discoloured rock is present either as IV HW Weathered a discontinuous framework or as corestones. Completely All rock material is decomposed and/or disintegrated to soil. The Decomposed/ V D original mass structure is still largely intact. Weathered All rock material is converted to soil. The mass structure and Residual Soil material fabric are destroyed. There is a large change in volume, VI R but the soil has not been significantly transported.
4.5 Field Parameter Characterisation
4.5.1 Residual Soil
Residual soil is formed by the in-situ decomposition (chemical weathering) or disintegration (mechanical weathering) of rock to a degree of softness which gives an unconfined compressive strength of the intact material of less than 700kPa. Residual soil generally transitions with depth into the parent rock from which it had been derived.
Detailed Design of the Midrand K109 Road Page 21 Site Geotechnical Investigations Report
Table 4.5_1 Probable Origin of Residual Soils in the Project Area
Parent Rock Lithological Material Formed Associated Engineering Impact Type Unit -Collapsible grain structure -Granite -Clayey-sand or sandy-clay (mica-rich) -Dispersive soils; Sand boils Acid Igneous -Vein Quartz -Clayey gravel -High permeability Rock -Pegmatite -Corestone -High erodibility; -Aplite -Gravel; cobbles and boulders -Good compaction/workability -Basalt -Clay (turf) -Expansive clay -Dolerite -Silty to sandy clay -Low shear strength Basic Igneous -Andesite -Corestone -Semi-pervious to impervious soil Rocks -Diorite -Gravel -Poor compaction/workability -Norite -Cobbles and boulders -Unstable slopes -Quartzite -Low shear strength -Clay, silt and sand Metamorphic -Schist -Unstable slopes -Gravel Rocks -Gneiss -Semi-pervious to impervious soil -Cobbles and boulders -Poor/good compaction/workability
4.5.2 Transported Soil
Transported soil is the material which has been transported by a natural agent (water, wind or gravity) during relatively recent geological times and which has not undergone lithification into a sedimentary rock or cementation into a pedogenic material.
Table 4.5_2 Probable Origin of Transported Soils in the Project Area
Transported Transportation Associated Description Source Rock Soil Type Soil Type Agent Engineering Impact -Unsorted, angular Coarse Talus Gravity Any gravels & boulders -Slope instability Colluvium within sandy soil matrix -Acid crystalline -Clayey sand -Collapsible grain Fine -Basic crystalline -Clay structure Hillwash Sheetwash Colluvium -Sedimentary -Sand -Heave rock -Clay/silt -High compressibility -Gravel -Dispersivity Alluvium - Streams/Gullies -Catchment rock -Sand/silt -Erosion -Clay Stream -Sand Lacustrine deposition into -Heave - -Mixed source -Silt Deposit pan, lake, pool, -High compressibility cavernous lake -Clay
4.5.3 Pedogenic Material
The Pebble Marker material includes ferricrete; calcrete and silcrete refer to soils which have become cemented by iron oxide, calcium carbonate and silica respectively. The development of pedogenic materials is classified in terms of five development stages; Initial precipitation within a soil; Powder form; Nodules; Honeycomb and Hardpan.
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Pedogenic materials require a certain climatic environment and moisture in some form for their development. The formation of ferricrete requires the percolation of water through a soil and the presence of a temporary fluctuating perched water table. The percolating water mobilizes ferrous iron, mostly obtained from decomposing mafic minerals and this ferrous iron is then carried downwards more or less to the base of such a perched water table. During this process the conversion to ferric iron takes place and the latter, being insoluble, is precipitated. The resultant ferricrete usually occurs at gully heads, hill slope- pediment and on pan and vlei-side slopes.
. Silcrete occurs at the coastal belt where the host grains have been cemented together by silica, while in the interior, replacement of calcretes has also occurred. Phoscrete often forms from calcrete which has been impregnated by phosphates derived from guano. Gypcrete occurs in the Upington region, but their occurrence seems to be associated with that of calcrete.
4.6 Key Geotechnical Constraints
The subsoils encountered in the test pits were examined in great detail and logged on site. The detailed pit logs/profiles are presented in Appendix A of this report:-
. Transported Soils:- Undifferentiated Top Soil: The project area is generally covered by a thin to medium-sized, top soil layer that is comprised of a dry, dark greyish brown to medium brown, loose, silty- to clayey-sand with moderate to weak plant growth (organics). The average thickness of this layer ranges between 0.02-0.05m often comprising of a mixed assemblage of other transported materials (including colluvium, hillwash, alluvium, organics, etc).
Talus: Coarse colluvium (when present) comprises the top 0.10m portion of the soil, usually mixed with a top undifferentiated soil material. It comprises silty- to clayey-sand with scattered, sub-rounded quartz and granitic gravels/laterite. This soil layer is often void and completely leached.
Hillwash: Fine colluvium frequently occurs along gully heads and on the lower side slopes adjacent to drainage channels. It comprises a thin, dry to moist, orange-brown to grey-brown, loose to medium-dense, silty- to clayey- sand with moderate to minor organic matter and is often underlain by hardpan ferricrete. This layer averages 0.40m thickness.
Alluvium: The gulley wash layer or alluvium is not widely-distributed across the project area but when observed, it is confined to the low-lying areas near drainage channels. It is typically gully wash and is comprised of a dark grey to brown, stiff to very stiff, potentially expansive sandy- to silty-clay. The grey colour indicates saturated, reducing conditions. The average thickness of this layer is around 0.35m.
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Pebble Marker: The gravel pebble marker indicates the transition between the transported and residual soils. The maximum thickness of this layer may be as high as 0.55m. It is typically defined as a damp to moist, pale grey-brown, moderately-dense, tightly to loosely-packed, sub-rounded to sub-angular quartz and granite gravel contained in a matrix of fine, ferruginous, silty- to coarse sand. It ranges from being nodular to hard pan ferricrete. . Bedrock Remnant:- Residual Soils: Residual soil formed as a result of the deep weathering of the bedrock is typically characterised by a suite of variegated colours including red-brown, stained dark brown, yellow-brown, and orange-brown. This soil layer is comprised of slightly-moist; loose to moderately-dense, ferruginous and reworked silty- to clayey-sand accompanied by gravel-sized, sub-angular quartz and minor medium-grained, hardpan ferricrete concretions. The average thickness ranges from 0.40-0.70m.
Weathered Granite: The saprolite layer comprises a red-brown to pink, strongly-weathered, kaolinised and highly permeable granite comprising of K- feldspar, quartz, plagioclase, mica and dark clay minerals (manganese and iron) and was logged as Saprolite in the test pits where it was observed. The average thickness of this layer is estimated to be around 0.75m and occupies depths of between 0.95-1.75m below ground surface.
. Granite: This layer comprises pink, moderately- to slightly-weathered and highly fractured granite comprising of K-feldspar, quartz, plagioclase, biotite, iron ores and minor clay minerals. The granite layer is the predominant lithology of the bedrock.
Detailed Design of the Midrand K109 Road Project Page: 24 Site Geotechnical Investigations Report
5 LABORATORY TESTING AND ANALAYSIS
5.1 General Overview
Sampling of representative soil horizons recovered from the trial pits was conducted by the field team. The collected samples were submitted to the RoadLab laboratory (Germiston) for standard analysis and testing aimed at determining the engineering properties. The RoadLab laboratory is a SANAS accredited laboratory. Some of the tests that were performed include the following:-
. Foundation Indicator tests (including full grading; Atterberg Limits and Hydrometer). . Analyses to determine the engineering characteristics of the unconsolidated materials. . MOD AASHTO density tests and the determination of the California Bearing Ratios (CBR) strength tests to determine efficacy of these materials for road construction and/ or platforms at the site.
. Quality/density measurements of in-situ materials.
5.2 Test Pitting & Profiling Results
Results obtained from the soil profiling of the test pits has revealed that the project area is covered by a very thin mantle of top layer characterised by an assemblage of transported materials underlain by residual and fresh granite/granodiorite of the Halfway House Granite Suite of the Basement Complex.
The geotechnical characteristics of the residual granite are mainly a function of its position within the Kyalami Land System Landscape. The soil cover across the project is generally thicker in the northern part of the territory. There is a generally reduced depth to bedrock towards the south (near areas in close proximity to the Glen Austin water pan).
Detailed Design of the Midrand K109 Road Project Page: 25 Site Geotechnical Investigations Report
Figure 3.2 Midrand K109 Road Project: Typical Soil Profile
Detailed Design of the Midrand K109 Road Project Page: 26 Site Geotechnical Investigations Report
5.3 Analytical Test Results
Modified AASHTO compaction, CBR tests as well as particle size distribution and Atterberg Limits were performed on the representative bulk soil samples collected from the various soil horizons. Due to the coarse-grained nature of the materials encountered, no undisturbed samples were collected
Particle size analysis (full grading) and indicator tests were undertaken on representative samples of the materials on site. These tests show that the transported soil materials have moderate clay content and a low- to medium Plasticity Index (PI). The residual soil material has a moderate to very high clay content and is characterised by a moderate PI. Generally, all the soil materials encountered on site fall under the category of “low potential”, expansive material. In most cases, the difference between hillwash and pebble marker is shown by the relatively higher content of sand and lower content of gravel in the hillwash.
The potential expansiveness of the materials encountered on site was calculated using the classification method of Van der Merwe (1964). The above results indicate that the project materials are classified as moderate to low expansive. A summary of the laboratory results are shown in Table 5.3_1:-
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Figure 3.2 Midrand K109 Road Design: Typical Laboratory CBR Test Result Sheet
Detailed Design of the Midrand K109 Road Page 28 Geotechnical Investigations Report
Table 5.3_1 Summary of Laboratory Results
Particle Size Depth Field Atterberg Limits TMH A8: CBR Values Date Sampling Test Lab Soil Soil Moisture (%) Modified ASHTO Material Sample Swell Results Date Pit No. Description (in-situ) Class No. Type GM Received 4.75 2.00 0.425 0.075 LS OMC MDD 90 93 95 97 98 100 From To Run LL (%) PI (mm) (mm) (mm) (mm) (%) (%) (kg/m3) (%) (%) (%) (%) (%) (%) 0.00 0.40 0.40 TP1/1 4624 Alluvium Silty-Sand Damp 74 68 43 29 30.0 10.0 4.9 1.60 12.4 1,927 0.74 4 8 10 14 15 19 G9 19-09-2014 16-08-2014 TP1 0.40 0.75 0.35 TP1/2 4623 Pebble Marker Silty-Sand Damp 74 58 42 20 28 8 4.1 1.80 11.2 2,027 0.31 7 11 13 17 20 24 G8 19-09-2014 0.75 1.75 1.00 TP1/3 4625 Residual Soil Clayey-Sand Moist 72 52 30 12 29.0 9.0 4.5 2.06 10.4 2,042 0.24 12 22 29 36 36 39 G7 12-09-2014 0.00 0.50 0.50 TP2/1 4626 Pebble Marker Clayey-Sand Damp 56 41 30 13 15.0 4.0 2.0 2.16 6.1 2,203 0.06 24 30 34 40 44 50 G6 12-09-2014 19-08-2014 TP2 0.50 1.10 0.60 TP2/2 4627 Residual Soil Clayey-Gravel Damp 59 46 30 16 18.0 5.0 2.4 2.08 7.1 2,100 0.15 14 24 30 35 38 43 G7 12-09-2014 1.10 1.50 0.40 TP2/3 4628 Saprolite Weath Granite Moist 97 80 46 25 31.0 12.0 5.5 1.49 12.1 1,960 0.38 5 7 8 10 12 14 G9 12-09-2014 0.00 0.40 0.40 TP3/1 4629 Hillwash Silty-Sand Dry 99 91 58 34 20.0 6.0 3.2 1.17 9.1 2,071 0.20 4 6 8 10 12 14 G10 12-09-2014 19-08-2014 TP3 0.40 1.50 1.10 TP3/2 4630 Pebble Marker Silty-Gravel Moist 97 74 49 24 34.0 14.0 7.1 1.53 9.4 2,051 0.29 14 22 27 38 44 56 G7 12-09-2014 0.00 0.30 0.30 TP4/1 4631 Pebble Marker Silty-Clay Damp 80 50 31 18 34.0 12.0 6.3 2.01 12.1 1,948 0.18 7 18 25 33 37 46 G7 12-09-2014 19-08-2014 TP4 0.30 0.90 0.60 TP4/2 4632 Residual Soil Silty-Sand Damp 48 36 25 10 23.0 9.0 4.3 2.29 9.1 2,095 0.10 9 20 27 32 34 39 G7 12-09-2014 0.90 1.50 0.60 TP4/3 4633 Saprolite Weath Granite Moist 93 74 39 28 37.0 11.0 5.7 1.59 12.1 1,964 0.17 7 14 19 21 22 24 G8 12-09-2014 0.00 0.35 0.35 TP5/1 4634 Hillwash Silty-Sand Damp 90 72 45 22 15.0 4.0 2.1 1.61 7.4 2,149 0.16 20 27 32 41 45 54 G6 12-09-2014 19-08-2014 TP5 0.35 0.85 0.50 TP5/2 4635 Residual Soil Silty-Sand Moist 77 70 44 19 18.0 5.0 2.7 1.67 9.1 2,116 0.10 8 14 18 23 26 31 G8 12-09-2014 0.00 0.30 0.30 TP6/1 4636 Pebble Marker Silty-Sand Damp 42 31 18 9 18.0 5.0 2.6 2.41 6.3 2,220 0.09 25 28 30 41 47 59 G6 12-09-2014 19-08-2014 TP6 0.30 0.60 0.30 TP6/2 4637 Residual Soil Clayey-Sand Damp 40 25 14 5 22.0 5.0 2.3 2.56 9.2 2,131 0.12 17 27 40 46 48 52 G6 12-09-2014 0.60 1.50 0.90 TP6/3 4638 Saprolite Weath Granite Moist 94 68 41 25 29.0 11.0 5.3 1.66 12.1 1,981 0.18 9 15 19 24 27 32 G7 12-09-2014 0.00 0.45 0.45 TP7/1 4639 Hillwash Silty-Sand Damp 99 90 66 42 22.0 8.0 3.8 1.02 10.3 2,023 0.57 3 5 6 8 8 10 G10 12-09-2014 19-08-2014 TP7 0.45 1.50 1.05 TP7/2 4640 Pebble Marker Silty-Gravel Moist 93 64 44 30 31.0 12.0 6.2 1.62 13.1 1,990 0.27 6 10 13 15 17 19 G8 12-09-2014 0.00 0.20 0.20 TP8/1 4641 Pebble Marker Silty-Sand Dry 98 93 69 42 26.0 11.0 5.4 0.96 11.1 1,985 0.33 3 4 5 6 6 7 G10 12-09-2014 19-08-2014 TP8 0.20 1.50 1.30 TP8/2 4642 Residual Soil Clayey-Sand Damp 88 76 57 40 42.0 18.0 9.0 1.27 14.9 1,860 0.91 4 6 8 9 10 11 G10 12-09-2014 0.00 0.60 0.60 TP9/1 4643 Hillwash Silty-Sand Damp 98 95 68 33 26.0 11.0 5.5 1.04 11.2 1,910 0.44 5 8 10 12 14 16 G9 12-09-2014 0.60 1.00 0.40 TP9/2 4644 Pebble Marker Silty-Gravel Damp 58 47 36 21 27.0 12.0 5.5 1.96 12.1 2,023 0.16 7 11 13 15 17 19 G8 12-09-2014 20-08-2014 TP9 1.00 1.75 0.75 TP9/3 4645 Residual Soil Clay Damp 99 82 68 41 29.0 7.0 3.5 1.09 12.1 1,865 0.73 4 6 8 10 10 12 G10 12-09-2014 1.75 2.50 0.75 TP9/4 4646 Saprolite Weath Granite Damp 96 87 59 36 34.0 10.0 5.0 1.18 13.3 1,940 0.74 3 5 6 8 8 10 G10 12-09-2014 0.00 0.30 0.30 TP10/1 4647 Hillwash Silty-Sand Damp 100 98 58 35 17.0 5.0 2.5 1.09 9.0 2,065 0.23 4 6 7 9 9 11 G10 12-09-2014 20-08-2014 TP10 0.30 0.55 0.25 TP10/2 4648 Alluvium Clayey-Sand Moist 85 81 60 30 24.0 10.0 5.2 1.29 11.4 1,997 0.25 6 9 11 15 17 22 G9 12-09-2014 0.55 0.85 0.30 TP10/3 4649 Pebble Marker Clayey-Gravel Wet 58 51 37 19 22.0 8.0 4.1 1.93 8.1 2,046 0.14 12 21 27 29 30 32 G7 12-09-2014 0.00 0.35 0.35 TP11/1 4650 Hillwash Silty-Sand Dry 100 98 71 37 16.0 4.0 1.7 0.94 11.4 1,933 0.31 5 7 9 11 12 14 G9 12-09-2014 20-08-2014 TP11 0.35 0.75 0.40 TP11/2 4651 Pebble Marker Clayey-Sand Moist 94 89 72 38 27.0 13.0 6.5 1.01 12.1 1,972 0.57 2 4 6 8 9 11 G10 12-09-2014 0.75 1.25 0.50 TP11/3 4652 Residual Soil Clayey-Gravel Moist 63 53 35 21 22.0 8.0 3.9 1.91 10.1 2,018 0.10 9 13 15 21 23 29 G8 12-09-2014 0.00 0.35 0.35 TP12/1 4653 Hillwash Silty-Sand Dry 51 48 34 21 23.0 9.0 4.7 1.94 10.3 2,010 0.19 5 13 18 20 22 24 G8 12-09-2014 20-08-2014 TP12 0.35 0.60 0.25 TP12/2 4654 Pebble Marker Clayey-Sand Moist 41 31 20 10 28.0 12.0 5.9 2.39 10.1 2,081 0.07 22 38 49 61 68 80 G5 12-09-2014
LL = Liquid Limit OMC = Optimum Moisture Content PI = Plasticity Index MDD = Modified Dry Density LS = Linear Shrinkage GM = Grading Modulus
Detailed Design of the Midrand K109 Road Page 29 Geotechnical Investigations Report Table 5.3_1 Summary of Laboratory Results
Particle Size Depth Field Atterberg Limits TMH A8: CBR Values Date Sampling Test Lab Soil Soil Moisture (%) Modified ASHTO Material Sample Swell Results Date Pit No. Description (in-situ) Class No. Type GM Received 4.75 2.00 0.425 0.075 LS OMC MDD 90 93 95 97 98 100 From To Run LL (%) PI 3 (mm) (mm) (mm) (mm) (%) (%) (kg/m ) (%) (%) (%) (%) (%) (%) 0.00 0.40 0.40 TP13/1 5428 Hill Wash Silty-Sand Dry 99 97 71 44 28 11 5.9 0.88 12.7 1,892 1.25 6 8 10 12 13 15 G9 17-11-2014 07-10-2014 TP13 0.40 0.65 0.25 TP13/2 5429 Pebble Marker Clayey-Gravel Damp 58 54 40 28 28 12 6.1 1.78 11.2 1933 0.58 9 15 19 23 25 29 G7 17-11-2014 0.65 1.60 0.95 TP13/3 5430 Saprolite Granite Damp 47 42 29 19 18 6 2.8 2.10 6.1 2,201 0.08 18 28 36 43 46 53 G6 17-11-2014 0.00 0.40 0.40 TP14/1 5431 Hill Wash Silty-Sand Damp 99 96 61 26 19 4 3.1 1.15 10.2 2,000 0.34 3 6 8 10 10 12 G10 17-11-2014 07-10-2014 TP14 0.40 0.65 0.25 TP14/2 5432 Pebble Marker Clayey-Gravel Dry 46 37 27 16 28 6 3.0 2.20 8.9 2,149 0.21 16 21 25 33 38 46 G7 17-11-2014 0.65 2.25 1.60 TP14/2 5433 Saprolite Granite Damp 91 80 57 38 24 5 2.4 1.25 11 1,984 0.32 6 9 11 14 15 18 G9 17-11-2014 0.00 0.40 0.40 TP15/1 5434 Hill Wash Silty-Sand Moist 100 98 67 28 17 6 2.9 1.07 8.1 2,094 0.13 6 10 13 17 20 24 G8 17-11-2014 0.40 0.70 0.30 TP15/2 5435 Alluvium Silty-Sand Dry 88 82 61 38 25 11 5.7 1.19 11.2 1,964 0.29 7 9 11 14 16 19 G9 17-11-2014 07-10-2014 TP15 0.70 0.90 0.20 TP15/3 5436 Pebble Marker Clayey-Gravel Damp 65 53 37 21 28 15 7.5 1.89 10.9 2,057 0.93 14 23 29 35 37 43 G7 17-11-2014 0.90 2.05 1.15 TP15/4 5437 Saprolite Granite Moist 48 40 25 14 26 7 3.5 2.21 8.2 2,086 0.24 16 26 32 41 45 54 G6 17-11-2014 0.00 0.42 0.42 TP16/1 5438 Hill Wash Silty-Sand Dry 98 95 72 35 28 14 6.7 0.98 12.2 1,910 0.92 3 7 9 11 12 14 G9 17-11-2014 07-10-2014 TP16 0.42 0.85 0.43 TP16/2 5439 Pebble Marker Clayey-Gravel Damp 65 53 38 18 32 12 6.1 1.91 10.4 1,984 0.24 8 12 14 19 22 27 G8 17-11-2014 0.85 2.45 1.60 TP16/3 5440 Residual Soil Clay Moist 72 58 43 27 37 14 7.0 1.72 16.1 1,822 1.34 3 5 7 8 9 10 G10 17-11-2014 0.00 0.30 0.30 TP17/1 5441 Hill Wash Silty-Sand Dry 96 91 61 32 24 10 5.0 1.16 10.4 1,986 0.33 5 7 8 11 13 15 G9 17-11-2014 0.30 0.70 0.40 TP17/2 5442 Alluvium Silty-Sand Dry 70 50 40 34 35 16 8.1 1.76 12.1 1,955 0.27 9 13 16 24 27 35 G8 17-11-2014 07-10-2014 TP17 0.70 1.90 1.20 TP17/3 5443 Pebble Marker Sand Damp 98 69 52 41 34 17 8.2 1.38 13.9 1,898 1.24 2 4 5 7 8 10 G10 17-11-2014 1.90 2.45 0.55 TP17/4 5444 Saprolite Granodiorite Moist 92 74 40 26 31 11 5.4 1.60 10.1 2,035 0.24 10 19 25 28 29 31 G7 17-11-2014 0.00 0.30 0.30 TP18/1 5445 Hill Wash Silty-Sand Dry 74 63 41 17 21 6 3.1 1.79 8.3 2,096 0.42 15 23 28 31 32 35 G7 17-11-2014 07-10-2014 TP18 0.30 0.65 0.35 TP18/2 5446 Pebble Marker Clayey-Gravel Dry 57 37 21 11 24 6 3.0 2.31 10.1 2,018 0.12 10 17 22 26 28 32 G7 17-11-2014 0.65 2.00 1.35 TP18/3 5447 Saprolite Granite Dry 84 62 39 23 28 10 4.8 1.76 11.2 2,028 0.65 6 11 14 19 21 26 G8 17-11-2014 0.00 0.45 0.45 TP19/1 5448 Hill Wash Silty-Sand Dry 100 94 61 29 23 11 5.2 1.16 8.1 2,074 0.11 7 15 21 26 29 35 G9 17-11-2014 07-10-2014 TP19 0.45 0.80 0.35 TP19/2 5449 Alluvium Silt Damp 90 70 51 30 29 13 6.6 1.49 12.1 2,018 0.63 4 7 9 11 12 14 G9 17-11-2014 0.80 2.25 1.45 TP19/3 5450 Saprolite Silty-Clay Damp 87 64 41 24 26 13 6.3 1.71 12.2 1,960 0.26 7 12 15 18 19 22 G8 17-11-2014 0.00 0.40 0.40 TP20/1 5451 Hill Wash Silty-Sand Dry 100 95 64 33 26 9 4.5 1.08 13.2 1,929 0.25 8 15 19 19 20 12 G9 17-11-2014 07-10-2014 TP20 0.40 0.65 0.25 TP20/2 5452 Pebble Marker Silty-Sand Dry 84 66 42 28 32 16 6.8 1.64 13.4 1,989 0.94 5 7 9 11 12 14 G9 17-11-2014 0.65 1.60 0.95 TP20/3 5453 Residual Soil Silt Damp 63 42 30 21 28 20 5.8 2.07 12.1 1,990 0.41 4 8 10 13 15 18 G9 17-11-2014 0.00 0.40 0.40 TP21/1 5454 Hill Wash Silty-Sand Dry 99 95 70 41 23 8 4.1 0.94 10.1 2,038 0.13 9 13 15 22 25 32 G9 17-11-2014 07-10-2014 TP21 0.40 0.75 0.35 TP21/2 5455 Alluvium Silty-Sand Damp 97 81 55 33 31 14 6.8 1.31 11 2,019 0.81 7 10 13 14 15 16 G9 17-11-2014 0.75 2.75 2.00 TP21/3 5456 Residual Soil Silty-Clay Moist 76 50 32 19 28 11 5.7 1.99 10.2 2,051 0.14 15 22 26 32 35 41 G7 17-11-2014 0.00 0.40 0.40 TP22/1 5457 Hill Wash Silty-Sand Dry 99 96 61 31 18 4 2.0 1.12 11.1 2,018 0.28 16 26 33 37 39 42 G9 17-11-2014 07-10-2014 TP22 0.40 0.90 0.50 TP22/2 5458 Pebble Marker Silty-Sand Damp 67 56 37 20 24 12 5.6 1.87 12.3 2,070 0.14 7 12 15 21 23 29 G8 17-11-2014 0.90 2.15 1.25 TP22/3 5459 Saprolite Silty-Clay Moist 98 91 61 37 27 14 6.7 1.11 12.4 2,032 0.78 12 19 24 27 28 31 G9 17-11-2014 0.00 0.30 0.30 TP23/1 5460 Hill Wash Silty-Sand Dry 86 75 46 20 - - 1.0 1.59 7.2 2,127 0.25 6 8 10 12 13 15 G9 17-11-2014 07-10-2014 TP23 0.30 0.55 0.25 TP23/2 5461 Pebble Marker Clayey-Gravel Dry 55 44 27 13 30 9 4.5 2.16 11.2 2,004 0.28 13 17 19 23 26 30 G7 17-11-2014 0.55 2.05 1.50 TP23/3 5462 Saprolite Granite Moist 93 59 41 25 35 15 7.0 1.75 12.2 1,961 0.18 12 17 20 25 28 33 G7 17-11-2014
LL = Liquid Limit OMC = Optimum Moisture Content PI = Plasticity Index MDD = Modified Dry Density LS = Linear Shrinkage GM = Grading Modulus
Detailed Design of the Midrand K109 Road Page 30 Site Geotechnical Investigations Report
Table 5.3_1 Summary of Laboratory Results
Particle Size Depth Atterberg Limits TMH A8: CBR Values Field Modified ASHTO Date Sampling Test Lab Soil Soil Moisture (%) Material Sample Swell Results Date Pit No. Description (in-situ) Class No. Type GM Received 4.75 2.00 0.425 0.075 LS OMC MDD 90 93 95 97 98 100 From To Run LL (%) PI 3 (mm) (mm) (mm) (mm) (%) (%) (kg/m ) (%) (%) (%) (%) (%) (%) 0.00 0.40 0.40 TP24/1 5463 Hill Wash Silty-Sand Dry ------08-10-2014 TP24 0.40 0.65 0.25 TP24/2 5464 Pebble Marker Silty-Sand Damp ------0.65 2.60 1.95 TP24/3 5465 Residual Soil Sand Damp ------0.00 0.30 0.30 TP25/1 5466 Hill Wash Silty-Sand Dry 78 73 42 19 17 4 2.1 1.66 7 2,096 0.10 16 23 27 35 39 47 G9 17-11-2014 08-10-2014 TP25 0.30 0.75 0.45 TP25/2 5467 Pebble Marker Silty-Gravel Dry 37 32 17 6 - - 1.4 2.45 6.1 2232 0.13 24 52 70 88 98 116 G5 17-11-2014 0.75 2.45 1.70 TP25/3 5468 Saprolite Granite Moist 83 54 40 22 18 4 2.1 1.84 9.2 2,083 0.29 9 16 20 26 28 34 G7 17-11-2014 0.00 0.16 0.16 - - Hill Wash Sand Dry ------17-11-2014 08-10-2014 TP26 0.16 0.60 0.44 TP26/2 5470 Alluvium Silty-Sand Dry 73 67 44 24 - - - 1.65 5.1 2,321 0.15 12 21 27 35 40 48 G7 17-11-2014 0.60 1.95 1.35 TP26/3 5471 Residual Soil Silt Damp 63 53 33 18 14 4 2.0 1.96 6.1 2,258 0.09 16 18 19 24 27 33 G7 17-11-2014 0.00 0.15 0.15 - - Hill Wash Silty-Sand Dry ------08-10-2014 TP27 0.15 0.20 0.05 - - Pebble Marker Clayey-Gravel Dry ------0.00 0.10 0.10 - - Hill Wash Silty-Sand Dry ------17-11-2014 0.10 0.65 0.55 TP28/2 5473 Pebble Marker Clayey-Gravel Damp 35 29 21 11 - - 1.0 2.39 8.1 2,192 0.09 19 27 32 48 57 73 G6 17-11-2014 08-10-2014 TP28 0.65 1.35 0.70 TP28/3 5474 Residual Soil Sand Moist 76 59 40 22 - - 1.7 1.79 9.1 2,108 0.12 15 24 29 38 43 53 G7 17-11-2014 1.35 2.65 1.30 TP28/4 5475 Saprolite Granite Moist 88 62 37 20 29 6 3.1 1.81 11.1 1,961 0.14 11 19 24 26 28 30 G7 17-11-2014 0.00 0.17 0.17 - - Hill Wash Silty-Sand Damp ------17-11-2014 0.17 0.50 0.33 TP29/2 5477 Pebble Marker Clayey-Gravel Dry 55 48 28 12 17 4 2.1 2.12 7.1 2,213 0.07 21 27 31 41 46 56 G6 17-11-2014 08-10-2014 TP29 0.50 1.20 0.70 TP29/3 5478 Residual Soil Silty-Sand Damp 60 53 31 13 22 5 2.3 2.03 8.1 2,183 0.09 16 24 30 37 41 48 G7 17-11-2014 1.20 2.20 1.00 TP29/4 5479 Saprolite Granite Damp 99 64 34 16 33 11 5.2 1.86 11.2 2,029 0.15 13 19 23 27 30 34 G7 17-11-2014 0.00 0.40 0.40 TP30/1 5480 Hill Wash Silty-Sand Dry 66 61 38 19 18 4 2.1 1.26 7.1 2,131 0.09 17 29 41 46 48 51 G6 17-11-2014 08-10-2014 TP30 0.40 0.65 0.25 TP30/2 5481 Pebble Marker Clayey-Gravel Dry 48 40 22 13 19 6 3.2 2.25 6.1 2,167 0.09 15 26 34 41 45 52 G6 17-11-2014 0.00 0.40 0.40 TP31/1 5482 Hill Wash Sand Dry 73 69 38 15 17 5 2.5 1.78 9.1 2,170 0.12 14 18 21 31 37 47 G7 17-11-2014 0.40 1.00 0.60 TP31/2 5483 Pebble Marker Clayey-Gravel Dry 72 43 24 11 23 7 3.3 2.22 9 2,049 0.18 6 12 16 20 22 27 G8 17-11-2014 08-10-2014 TP31 1.00 1.35 0.35 TP31/3 5484 Residual Soil Silty-Sand Damp 77 60 34 15 20 4 1.9 1.91 8.2 2,084 0.11 21 30 36 46 50 60 G6 17-11-2014 1.35 1.95 0.60 TP31/4 5485 Saprolite Granite Damp 39 33 22 13 16 4 2.1 2.32 8.1 2,196 0.10 18 32 41 47 50 56 G6 17-11-2014 0.00 0.30 0.30 TP32/1 5486 Hill Wash Sand Dry 98 93 52 38 23 7 3.3 1.17 10.1 2,015 0.16 11 16 20 23 25 28 G7 17-11-2014 08-10-2014 TP32 0.30 0.60 0.30 TP32/2 5487 Pebble Marker Clayey-Gravel Dry 49 37 18 10 21 9 4.3 2.35 7.1 2,178 0.08 23 42 54 63 67 76 G5 17-11-2014 0.00 0.24 0.24 TP33/1 5488 Hill Wash Silty-Sand Dry 100 99 64 29 18 6 3.2 1.08 7.1 2,102 0.15 9 15 19 22 24 27 G7 17-11-2014 08-10-2014 TP33 0.24 0.50 0.26 TP33/2 5489 Alluvium Silty-Sand Damp 94 92 56 36 23 10 4.7 1.16 10.1 1,980 0.27 4 6 8 11 12 15 G10 17-11-2014 0.50 0.75 0.25 TP33/3 5490 Pebble Marker Clayey-Gravel Dry 47 42 25 14 18 6 3.2 2.19 9.1 2,122 0.19 23 30 35 38 39 42 G6 17-11-2014 0.00 0.30 0.30 TP34/1 5491 Hill Wash Sand Dry 100 99 39 15 - - 0.6 1.47 7.2 2,072 0.14 7 10 12 13 14 16 G9 17-11-2014 08-10-2014 TP34 0.30 0.40 0.10 TP34/2 5492 Pebble Marker Clayey-Gravel Dry 67 65 31 14 - - - 1.90 9 2,136 0.13 10 18 24 32 37 45 G7 17-11-2014 0.00 0.50 0.50 TP35/1 5493 Hill Wash Sand Dry 98 94 45 21 - - 0.9 1.40 7.4 2,110 0.35 6 11 14 16 18 20 G9 17-11-2014 08-10-2014 TP35 0.50 0.95 0.45 TP35/2 5494 Pebble Marker Clayey-Gravel Dry 39 36 20 10 - - - 2.34 5.2 2,287 0.09 27 43 54 57 58 61 G5 17-11-2014
LL = Liquid Limit OMC = Optimum Moisture Content PI = Plasticity Index MDD = Modified Dry Density LS = Linear Shrinkage GM = Grading Modulus
Detailed Design of the Midrand K109 Road Page 31 Site Geotechnical Investigations Report Table 5.3_1 Summary of Laboratory Results
Particle Size Depth Field Atterberg Limits TMH A8: CBR Values Date Sampling Test Lab Soil Soil Moisture (%) Modified ASHTO Material Sample Swell Results Date Pit No. Description (in-situ) Class No. Type GM Received 4.75 2.00 0.425 0.075 LS OMC MDD 90 93 95 97 98 100 From To Run LL (%) PI 3 (mm) (mm) (mm) (mm) (%) (%) (kg/m ) (%) (%) (%) (%) (%) (%) 0.00 0.45 0.45 TP36/1 5495 Hill Wash Sand Dry 100 99 47 24 - - - 1.30 7.1 2,146 0.16 12 19 23 28 31 36 G9 17-11-2014 0.45 0.85 0.40 TP36/2 5496 Alluvium Sand Dry 83 68 36 17 - - - 1.79 6.1 2,219 0.18 17 24 28 37 41 50 G7 17-11-2014 08-10-2014 TP36 0.85 1.70 0.85 TP36/3 5497 Pebble Marker Clayey-Gravel Damp 54 51 32 17 13 6 3.1 2.00 6.1 2,248 0.04 25 39 49 55 57 63 G5 17-11-2014 1.70 2.20 0.50 TP36/4 5498 Residual Soil Clay Moist 69 55 40 21 17 6 2.8 1.84 8.2 2,051 0.10 17 23 27 38 44 55 G7 17-11-2014 0.00 0.50 0.50 TP37/1 5499 Hill Wash Silty-Sand Damp 98 97 53 20 25 7 3.3 1.30 11 1,975 0.24 6 8 10 14 15 19 G9 17-11-2014 09-10-2014 TP37 0.50 1.10 0.60 TP37/2 5500 Pebble Marker Clayey-Gravel Damp 87 80 52 34 - - - 1.34 6.1 2190 0.18 8 12 15 20 23 29 G9 17-11-2014 1.10 1.65 0.55 TP37/3 5501 Residual Soil Silty-Sand Damp 69 64 42 26 17 6 2.7 1.68 7.2 2,182 0.09 10 16 20 26 30 36 G7 17-11-2014 0.00 0.40 0.40 TP38/1 5502 Hill Wash Silty-sand Dry 99 97 43 25 20 6 3.2 1.35 8 2,080 0.33 4 8 10 12 14 16 G9 17-11-2014 09-10-2014 TP38 0.40 0.65 0.25 TP38/2 5503 Alluvium Clayey-Gravel Damp 67 62 36 21 19 7 3.7 1.81 10.2 2,076 0.18 9 13 16 19 21 24 G8 17-11-2014 0.65 1.35 0.70 TP38/3 5504 Pebble Marker Silty-Sand Dry 46 41 25 11 18 6 2.9 2.23 7.1 2,204 0.10 14 23 29 39 44 54 G7 17-11-2014 0.00 0.25 0.25 - - Hill Wash Silty-Sand Dry ------17-11-2014 0.25 0.55 0.30 TP39/2 5505 Alluvium Silty-Sand Dry 71 66 38 24 21 9 4.3 1.72 10.1 2,029 0.17 6 13 18 23 25 30 G8 17-11-2014 09-10-2014 TP39 0.55 1.35 0.80 TP39/3 5506 Pebble Marker Clayey-Gravel Dry 42 30 16 9 - - 0.8 2.45 10.1 2,079 0.26 16 29 37 45 49 57 G6 17-11-2014 1.35 2.65 1.30 TP39/4 5507 Saprolite Granite Moist 69 62 38 16 22 8 4.0 1.84 10.2 2,065 0.15 8 12 14 19 22 27 G8 17-11-2014 0.00 0.25 0.25 - - Hill Wash Silty-Sand Dry ------17-11-2014 09-10-2014 TP40 0.25 0.45 0.20 TP40/2 5509 Alluvium Silty-Sand Damp 54 50 31 20 27 14 6.9 1.99 9.2 2,151 0.35 9 17 23 31 34 42 G7 17-11-2014 0.45 1.80 1.35 TP40/3 5510 Pebble Marker Clayey-Gravel Damp 58 46 29 20 18 3 1.5 2.05 8.1 2,130 0.09 21 34 42 46 48 52 G6 17-11-2014 0.00 0.35 0.35 TP41/1 5511 Hill Wash Silty-Sand Dry 100 98 51 29 19 6 2.8 1.22 12.2 1,980 0.33 4 8 10 13 15 18 G9 17-11-2014 09-10-2014 TP41 0.35 0.90 0.55 TP41/2 5512 Alluvium Sand Dry 99 98 70 48 27 11 5.7 0.84 17.1 1,761 0.85 1 2 2 2 3 3 G10 17-11-2014 0.90 2.45 1.55 TP41/3 5513 Residual Soil Clay Damp 100 97 63 39 29 12 6.0 1.01 13.3 1,862 0.92 4 7 9 11 11 13 G9 17-11-2014 0.00 0.75 0.75 TP42/1 5514 Hill Wash Hill Wash Damp 99 97 60 35 34 12 6.1 1.08 14.2 1,798 1.68 1 2 2 2 3 3 G10 17-11-2014 09-10-2014 TP42 0.75 1.60 0.85 TP42/2 5515 Alluvium Alluvium Damp 99 83 50 24 - - - 1.43 10.4 1,962 0.12 8 13 16 21 24 29 G9 17-11-2014 1.60 2.30 0.70 TP42/3 5516 Residual Soil Residual Soil Moist 98 95 60 37 24 5 2.7 1.08 14.2 1,981 2.35 1 2 2 2 3 3 G10 17-11-2014 0.00 0.85 0.85 TP43/1 5517 Hill Wash Silty-Sand Dry 100 97 60 37 27 11 5.5 1.06 14.3 1,858 2.46 1 2 3 3 3 3 G10 17-11-2014 09-10-2014 TP43 0.85 1.90 1.05 TP43/2 5518 Alluvium Clay Dry 95 93 70 39 44 21 10.4 0.98 22.1 1,618 2.57 1 2 2 3 4 5 G10 17-11-2014 1.90 2.50 0.60 TP43/3 - Residual Soil Silty-Sand Moist ------0.00 0.40 0.40 TP44/1 - Alluvium Clay Moist ------09-10-2014 TP44 0.40 0.65 0.25 TP44/2 - Residual Soil Sand Moist ------0.00 0.20 0.20 TP45/1 - Hill Wash Silty-Sand Dry ------0.20 0.70 0.50 TP45/2 - Pebble Marker Silty-Gravel Dry ------09-10-2014 TP45 0.70 1.10 0.40 TP45/3 - Residual Soil Silty-Clay Damp ------1.10 1.65 0.55 TP45/4 - Saprolite Granite Damp ------0.00 0.30 0.30 TP46/1 5525 Hill Wash Silty-Sand Dry 74 63 42 26 27 11 5.7 1.69 12.1 1,971 0.35 7 12 15 18 19 22 G8 17-11-2014 09-10-2014 TP46 0.30 0.85 0.55 TP46/2 5526 Pebble Marker Clayey-Gravel Damp 98 95 82 50 45 20 10.1 0.73 22.2 1,633 1.74 2 4 6 6 7 7 G10 17-11-2014 0.85 2.25 1.40 TP46/3 5529 Residual Soil Granite Moist 82 70 54 31 35 17 8.3 1.45 18.4 1,808 1.22 4 5 6 7 8 9 G10 17-11-2014
LL = Liquid Limit OMC = Optimum Moisture Content PI = Plasticity Index MDD = Modified Dry Density LS = Linear Shrinkage GM = Grading Modulus
Detailed Design of the Midrand K109 Road Project Page 32 Site Geotechnical Investigations Report
Table 5.3_1 Summary of Laboratory Results
Particle Size Depth Atterberg Limits TMH A8: CBR Values Field Date Sampling Test Lab Soil Soil Moisture (%) Modified ASHTO Material Sample Swell Results Date Pit No. Description (in-situ) Class No. Type GM Received 4.75 2.00 0.425 0.075 LS OMC MDD 90 93 95 97 98 100 From To Run LL (%) PI (mm) (mm) (mm) (mm) (%) (%) (kg/m3) (%) (%) (%) (%) (%) (%) 0.00 0.65 0.65 TP47/1 5527 Hill Wash Silty-Sand Dry 98 95 71 42 25 8 4.0 0.92 15.1 1,860 0.34 6 8 9 11 13 15 G9 17-11-2014 0.65 1.35 0.70 TP47/2 5528 Pebble Marker Clayey-Gravel Damp 73 56 47 36 35 19 9.4 1.61 13.1 1,883 0.57 5 7 9 13 15 19 G9 17-11-2014 08-10-2014 TP47 1.35 1.90 0.55 TP47/3 5529 Residual Soil Silty-Clay Damp 63 58 42 24 32 13 6.5 1.76 13.1 1,912 0.14 5 11 15 21 25 31 G8 17-11-2014 1.90 2.25 0.35 TP47/4 5530 Saprolite Dolerite Damp 93 82 62 46 37 15 7.5 1.10 19.1 1,742 0.87 3 4 5 7 7 9 G10 17-11-2014 0.00 0.60 0.60 TP48/1 5531 Hill Wash Silty-Sand Dry 99 95 61 33 30 15 7.5 1.11 12.1 1,946 0.34 4 6 7 11 13 17 G10 17-11-2014 0.60 1.05 0.45 TP48/2 5532 Pebble Marker Clayey-Gravel Dry 74 65 47 24 32 17 8.4 1.64 14.1 1,943 0.48 2 4 5 7 9 11 G10 17-11-2014 09-10-2014 TP48 1.05 1.70 0.65 TP487/3 5533 Residual Soil Silty-Clay Damp 93 62 37 25 36 15 7.5 1.76 13.2 1,917 0.52 7 10 12 15 17 20 G9 17-11-2014 1.70 2.30 0.60 TP48/3 5534 Saprolite Granite Moist 93 65 48 39 33 16 8.1 1.48 13.2 1,946 0.51 3 5 6 7 7 8 G10 17-11-2014
LL = Liquid Limit OMC = Optimum Moisture Content PI = Plasticity Index MDD = Modified Dry Density LS = Linear Shrinkage GM = Grading Modulus
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5.4 Dynamic Cone Penetration Test Survey
Dynamic Cone Penetrometer (DCP) tests were conducted with the aim of calculating of the bearing capacity in unconsolidated materials and use the results to classify in-situ road, sub-grade materials (TRH4). DCP tests were carried out to a depth of 1.0m at 200m and 100m spaced intervals (reconnaissance and main survey programmes, respectively) A total of 59 DCP stations were tested with a one-meter instrument (23 sounding stations during the reconnaissance phase and 36 stations during the main survey). Results of the DCP tests are shown in the Appendix.
Figure 3.2 Midrand K109 Road Design: Typical DCP Survey Profile
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6 ENGINEERING AND GEOTECHNICAL APPRAISAL
6.1 General Overview
The subsoil conditions prevailing along the proposed route are highly variable and often unpredictable, with significant variations occurring within small distances. The following geotechnical findings are based on the results obtained from the field and laboratory tests. A detailed review of the excavated test pits has revealed that the project site is underlain by granites and granodiorites assigned to the Halfway Granite suite of the Basement Complex. Deep weathering of the Basement rocks has led to the alteration of the mineral assemblages of the parent rock resulting into weathered rocks, saprolite and/or residual soil. Greenstone remnants that occur within the Basement Johannesburg Dome were observed as locally weathered greenish, mafic rich rocks. Immediately overlying remnants of the bedrock is the transitional, gravel-sized pebble marker layer comprising of a pale grey-brown, moderately-dense, tightly to loosely-packed, sub- rounded to sub-angular quartz and granite gravel contained in a matrix of fine, ferruginous, silty- to coarse sand. In most cases, the pebble marker layer is inconsistent in material composition and sometimes missing from the general location indicating probable erosion and/or non-deposition of the material. The top portion of the project area is comprised of transported materials including hillwash, gulley wash, pedogenic materials, and a very thin layer of undifferentiated top soil.
6.2 Geological Characteristics
The soil type or texture of a residual soil can usually be predicted from prior knowledge of the mineralogical composition of its parent material. For example, residual granite comprises a silty- or clayey-sand, derived from the decomposition of feldspar and quartz, while igneous rocks such as dolerite or basalt decompose mostly to form expansive clay.
Table 6.2_1 Probable Origin of Residual Soils in the Project Area
Parent Rock Lithological Material Formed Associated Engineering Impact Type Unit -Collapsible grain structure -Granite -Clayey-sand or sandy-clay (mica-rich) -Dispersive soils; Sand boils Acid Igneous -Vein Quartz -Clayey gravel -High permeability Rock -Pegmatite -Corestone -High erodibility; -Aplite -Gravel; cobbles and boulders -Good compaction/workability -Basalt -Clay (turf) -Expansive clay -Dolerite -Silty to sandy clay -Low shear strength Basic Igneous -Andesite -Corestone -Semi-pervious to impervious soil Rocks -Diorite -Gravel -Poor compaction/workability -Norite -Cobbles and boulders -Unstable slopes -Quartzite -Low shear strength -Clay, silt and sand Metamorphic -Schist -Unstable slopes -Gravel Rocks -Gneiss -Semi-pervious to impervious soil -Cobbles and boulders -Poor/good compaction/workability
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6.3 Geotechnical Appraisal
In general, the project area is flat with soil cover relatively thick to moderate and ranging from surface to about 1.75m below surface. Certain soils present problems to civil engineering developments due to the specific conditions in which these soils occur. The risk of geotechnical hazards are considered moderate to low although a thorough understanding of the geological model may be required prior to development. A summary of key geotechnical constraints is given in Table 7.2_1. Fatal geotechnical flaws which would limit the proposed development may be caused by the following key issues:- . Collapsible soils cause damage due to differential settlement. . Expansive soils cause damage due to continual heave and shrinkage . Highly compressible or soft soils cause damage due to continual heave and shrinkage . Erodible or dispersive soils cause damage due to erosion of colloidal particles . Pedogenic materials causing problems due to variable conditions . Steep slopes and unstable natural slopes causing problems due to variable conditions . Groundwater levels and seepage . Flooding . Excavatability
Table 6.3_1 Key Geotechnical Constraints
Constraint Explanation Quaternary alluvial clay and silt deposits are typically poorly consolidated and unlithified. These deposits may settle if unsupported or overloaded. The presence Settlement of proposed road of localised, un-engineered fill material may also result in a differential settlement formations and structures hazard. Dependent on the state of weathering, localised areas of extremely weathered granite may result in differential settlement of overlying clays. Although project area is a relatively low gradient, transported weathered material Slope stability can be susceptible to shallow soil failure (soil creep, slumping, collapse) in areas of increased gradient. Weathering bearing capacity within soft clay material or unconsolidated alluvial Bearing capacity material can result in loss of stability or potential collapse of structures during the construction phase of the development. Clay derived from granite bedrock is likely to be moderately- to highly-reactive and subjective to considerable shrinkage or swelling in response to changes in Shrink swelling moisture. Highly expansive clay can cause unexpected ground movements that are able to cause damage to road infrastructure and building structures. During flood events, local creeks may serve as drainage channels for storm water Erosion resulting in erosion of soft sediment and bedrock.
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6.4 Project Geotechnical Characteristics
6.4.1 Undifferentiated Transported Soil
Generally, the soil profile is fairly uniform and as such, the project site was not divided into different engineering geological zones. The excavatability characteristics based on the TLB refusal and an inspection of the test pits indicate that founding penetration will be limited from an average of 0.85m and a minimum of 0.60m. The pedogenic materials encountered as pebble marker may be a clear indicator that a perched water table should be expected during and after periods of high rainfall. Appropriate surface and subsurface drainage will be required in all areas, especially where the subgrade material is comprised of impermeable clayey soils, with the aim of preventing the artificial development of a perched water table under the road surface.
6.4.2 Hillwash
The fine colluvium (Hillwash) layer was encountered in 6 test pits excavated on site from ground surface up to a depth of 0.60m below ground level. It comprises a thin, dry to moist, orange-brown to grey-brown, loose to medium-dense, silty- to clayey-sand with moderate to minor organic matter and is often underlain by hardpan ferricrete. Hillwash is considered to be a generally low density compressible soil constituting low density, compressible soil that classifies a very poor subgrade when uncompacted.
6.4.3 Alluvium
Gulleywash (alluvium) is confined to the drainage path areas and may be observed from ground depth to a depth of 0.40m below ground level. Alluvium is comprised of a dark grey to brown, stiff to very stiff, potentially expansive sandy- to silty-clay.
The estimated allowable bearing pressure is in the region of 50-100kPa, but will be prone to consolidation settlements and/or heave movements (in correspondence with fluctuating moisture levels).
6.4.4 Pebble Marker
The gravel pebble marker constitutes pedogenic materials in the area and indicates the transition between the transported and residual soils. It is usually observed in 9 test pits from an average depth of 0.25m to a maximum depth of 1.50m below ground level. It is typically defined as a damp to moist, pale grey-brown, moderately-dense, tightly to loosely-packed, sub-rounded to sub-angular quartz and granite gravel contained in a matrix of fine, ferruginous, silty- to coarse sand.
The geotechnical properties of pedocretes depend on three factors; the texture of the host or parent material; the stage of development (i.e. the extent to which it has been cemented or replaced) and; the nature of the cementing or replacing mineral.
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Pedocretes can therefore be expected to exhibit certain differences in behaviour from those of traditional materials. In essence, these differences render the geotechnical behaviour of pedocretes less predictable by means of traditional laboratory tests.
6.4.5 Residual Soil
This altered residual granite remnant material (or Residual Soil) is generally encountered from a depth of 0.20 to 1.75m (average intersection depth of 0.56m below ground level). Residual soil formed as a result of the deep weathering of the parent bedrock and is typically characterised by a suite of variegated colours including red-brown, stained dark brown, yellow-brown, and orange-brown.
This soil layer is comprised of slightly-moist; loose to moderately-dense, ferruginous, and reworked silty- to clayey-sand accompanied by gravel-sized, sub-angular quartz and minor medium-grained, hardpan ferricrete concretions. The estimated allowable bearing pressure is in excess of 100kPa (depending on the degree of cementation). During the weathering process, quartz remains unaltered in the form of sand grains, mica remains partially unaltered and the feldspar becomes kaolinised by the chemical reaction with water charged with carbon dioxide. In areas of relatively high rainfall and conditions conducive to leaching, the colloidal kaolinite is largely removed in suspension by percolating groundwater, leaving behind a soil with a collapsible grain structure.
6.4.6 Weathered Granite
Saprolite material was encountered generally from a depth of 0.30 to 1.00m (with average intersection depth of 0.95m below ground level). This layer comprises a red- brown to pink, strongly-weathered, kaolinised and highly permeable granite comprising of K-feldspar, quartz, plagioclase, mica and dark clay minerals (manganese and iron).
6.4.7 Granite
This layer comprises pink, moderately- to slightly-weathered and highly fractured granite comprising of K-feldspar, quartz, plagioclase, biotite, iron ores and minor clay minerals. The granite layer, together with granodiorite forms the predominant lithology of the bedrock. The estimated allowable bearing pressure is in excess of 250kPa.
6.5 Probable Impact on Road Design & Construction
6.5.1 Collapsible Soils
A soil with a collapsible grain structure may be defined as a soil which can withstand relatively large imposed stresses with small settlements at low in-situ moisture content, but will exhibit a decrease in volume and associated additional settlement with no increase in the applied stress if wetting up occurs. The change in volume is associated with a change in soil structure (collapse of grain structure).
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The application of repeating dynamic loads, such as heavy vehicle traffic on a road may be sufficient to cause shear failure of the bridging colloidal between collapsible soil grains and induce collapse.
In addition to problems with the collapse of the road subgrade, the substantial reduction in volume that occurs with the compaction of the pavement layers must be taken into consideration in the estimation of material quantities for fills constructed from borrow areas or cuttings formed in soils with a collapsible grain structure.
In South Africa, collapse settlement is the term applied to the additional settlement which occurs due to the wetting up of a partially saturated collapsible soil under load. The most well-known occurrence of collapsible grain structure is within the residual soils derived from the granite of the Basement Complex.
6.5.2 Expansive Soils
Soils in which variations in moisture content result in volumetric change (i.e. swell or shrinkage of the soil skeleton) are defined as expansive soils. In residual soils, the expansive clays originate from the in-situ chemical weathering of rock. In transported soils, alluvial deposits along streams from a variety of rocks in the catchment area may contain expansive soils. The driving comfort of roads can be seriously affected by the movements caused by underlying expansive clays. Differential movements due to expansive clay may also cause problems at the approach contacts at bridges and at drainage structures such as culverts crossing underneath roads.
6.5.3 Soft Clays
It is commonly understood that soft clays give shear strength, compressibility and severe time related settlement problems. South African soft clay deposits are relatively small in lateral extent and are generally highly-variable, but may extend to considerable depths of up to 40m in places.
Soft clays can cause severe problems to large road embankments and crossings. The problems include stability failures, construction problems and long-term settlement. Differential settlement of large embankments on soft clay is major problems. In areas of fairly deep clays embankments may settle up to 30% of their height (i.e. more than 2m for a 7m high embankment) and this settlement may continue for up to 10 years.
6.5.4 Dispersive Soils
Dispersion can occur in any given soil with a high percentage of exchangeable sodium percentage (ESP), causing internal erosion and eventually piping through embankment dams. The tendency for dispersive erosion in a given soil depends upon such variables as the mineralogy and chemistry of the clay and the dissolved salts in the soil water and the eroding water.
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The main property of the clay governing the susceptibility to dispersion piping is the percentage absorbed sodium cations on the surface of the clay particles relative to the quantities of other polyvalent cations (calcium, magnesium or aluminium).
Dispersive soils normally do not affect roads, except for serious erosion problems on the slopes of cuttings and fill embankment side slopes.
6.5.5 Pedogenic Materials
The pedogenic development process commences with the precipitation of fine particles of the relevant material and in time these increase in concentration. Accretion of these particles leads first to soft, discrete nodules which consist mostly of the precipitated material that cement soil particles. Gradually, these nodules coalesce into a sponge-like, hard mass full of small cavities, the whole mass having a honeycomb structure. The cavities are usually filled with remnants of the host soil although the cementing material may already have become quite hard.
The filling of these cavities with the precipitate eventually results in rock-like hardpan. Hardpan can also develop without passing through a nodular or honeycomb stage. The development of these materials can come to an end at any stage and not all stages need to be passed through during the process of formation.
The occurrence of shallow hardpan pedogenic materials may severely affect the surfaces of gravel roads due to the presence of softer patches in the hardpan material, because the softer patches are removed by the passing traffic leaving a very uneven road surface. This occurs on many gravel roads in the arid western parts of South Africa, due to the shallow occurrence of hardpan calcrete.
6.5.6 Slope Instability
Earth failures mean the movement of a large mass of soil along a more or less definite surface. In most cases the earth mass remains intact during the first stages of movement, but finally it becomes distorted and broken up as movement progresses. Anything that results in a decrease in soil strength or an increase in soil stress contributes to instability.
Planar failure can also occur on the soil/rock contact where the underlying rock mass has steeply dipping bedding planes. Wedge failures are common in rock that is highly jointed (e.g. underlying granite near the Glen Austin water pan).
6.6 Hydrogeology
The Johannesburg Dome represents a typical hard rock environment with three potential aquifer systems namely; a shallow primary, weathered aquifer system; a deep aquifer system in unweathered granitoids and associated fractures, joints, discontinuities within the rock mass and; a perched aquifer occurring in hardpan ferricrete and shallow bedrock units.
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In addition to shallow bedrock conditions, groundwater is sometimes perched on low- permeability hardpan ferricrete and clayey layers (such as low permeability clayey, residual, ultramafic rocks and greenstone remnants). The perched aquifer found along hardpan ferricrete often discharges groundwater into drainage channels.
Generally, surface water shows a close relationship with the groundwater occurrences. In retrospect, the shallow weathered aquifer exhibits a close relationship with seasonal effects. Groundwater discharge areas are mainly associated with drainage channels, flood plains and water pans. The remainder of the area may be classified as a recharge zone. Within the project area, slow groundwater seepage was encountered in TP10 and also from two historic test pits (OTP2 and OTP3).
Subsurface attenuation layers (such as shallow bedrock, pedogenic horizons/pebble marker and clayey alluvial soils) are potential areas for perched water levels during the wetter months. The average groundwater seepage level is recorded at 0.72m. However, no groundwater level information was available from the existing boreholes on site.
6.7 Structural Foundations & Sidewall Stability
Existing slopes and embankments or newly exposed deep cuts or excavations are all susceptible to slides, slumps or failures. No areas of potential ground instability were noted during the site investigation phase. The general founding conditions on the project are apparently favourable. However, the stability of a sidewall remains a function of the moisture content of the soil. If the moisture content of the soil increases due to poor surface drainage, unstable conditions may occur. In addition, the presence of seepage water within an excavation must be regarded as a warning sign of unstable sidewall.
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7 INTERPRETATIONS AND DESIGN RECOMMENDATIONS
7.1 Site Preparation
Generally, the soil profile is fairly uniform and as such, the project site was not divided into different engineering geological zones. The excavatability characteristics based on the TLB refusal and an inspection of the test pits indicate that founding penetration will be limited from an average of 0.85m and a minimum of 0.60m.
The pedogenic materials encountered as pebble marker may be a clear indicator that a perched water table should be expected during and after periods of high rainfall. Appropriate surface and subsurface drainage will be required in all areas, especially where the subgrade material is comprised of impermeable clayey soils, with the aim of preventing the artificial development of a perched water table under the road surface.
7.2 Earth Works
From the generally moderate slope of the site, it is anticipated that cuts and fills will be of the order of less than 1m. Any surplus material from the weathered granite and residual soil may be stockpiled and used directly. Basic sorting may be required during the bulk earthworks operation with the aim of excluding larger boulder materials in isolated areas on site. Cuts and fills deeper than 2m will generally begin to encounter hard, weathered, fractured granite.
The fills should be placed in layers not exceeding 0.20m loose thickness and compacted to a minimum of 93% Modified AASHTO maximum dry density at 2% wet of optimum moisture content. Boulders larger two-thirds of the layer thickness must not be included in the fill material. Both during and after the road construction, the site should be well graded to permit water drain away readily and prevent ponding anywhere on the ground surface. All terraces and earthworks in general should be sloped to a gradient of not less than 1 vertical in 50 horizontal, to prevent water ingress into the subsoil since most of these soils are significantly permeable.
7.3 Geotechnical Recommendations
Roads can be seriously affected by the collapse of underlying soils caused by the dynamic loads imparted by the traffic. Prevention of water ingress to the road foundation is not necessarily the appropriate solution to prevent damage. Interpreting the results of the laboratory tests has established the presence and extent of collapsible soils along the proposed route. The reduction of the in situ material volume due to collapse must be included into the calculation of the required volumes of road construction materials.
. Appropriate surface and subsurface drainage is required to be provided in all cut areas, especially where the subgrade material is comprised of impermeable clayey soils. Cut off drains should be provided with the aim of diverting surface water away from the pavement. Run-off from building roofs should be piped from gutters, through down-pipes and discharged into the stormwater reticulation system.
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Disposal of stormwater should be conducted in conformity to the local administering authority regulations. . Specific attention is required where drainage structures pass underneath the road to prevent ponding of water. Fill areas should be similarly drained and all culverts should be adequately sized to take into account, the increasingly impermeability of the road reserve area. All road cuts should be inspected for stability soon after the excavations. . Certain expansive clay horizons (if of limited thickness), should be removed completely and replaced with suitable imported material. The cuts should be provided with nominal slope angles and protected from erosion by grassing or other means. This action is important especially in the highly erodable areas where highly micaceous, clayey- to sandy-silts was observed. Any blasting that may take place should be controlled. . No large trees should be allowed to grow inside the road reserve. Damming of the embankments in the watercourse areas during high rainfall periods, caused by inadequate culvert design, should be avoided. . Road embankments can be severely affected by settlement and instability due to the presence of soft clays. The solution to stability problems will mostly be to either flatten the side slopes of the embankment or to provide stabilising berms to act as counterweights. . Appropriate construction procedures to monitor settlement and possible instability should be conducted during the entire road construction period.
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8 CONCLUSIONS
This report contains the results of a site geotechnical investigation carried out on the portion ear-marked for the construction of the K109 Road in the Midrand Area.
. The area earmarked for the K109 road construction lies within the Glen Austin Agricultural Holdings of the Midrand Area.
. The project area is underlain by weathered granites, granodiorites and remnants of mafic and ultramafic intrusives assigned to the Halfway House Granite Group of the Basement Complex.
. Locally, the residual, reworked granites are intensely to moderately weathered and often associated with a thin, colluvial sandy gravel and a thick sandy hillwash. The near surface hill wash is a low density, partly saturated soil of significant collapse potential whilst some of the weathered granites have produced clay-rich, loamy soil having significant plasticity and are often of medium swelling/shrinkage potential.
. Most of the soils sitting on top of the weathered granites are ranked between G5 to G10 (under the COLTO materials classification system).
. Based on the results obtained from the geotechnical investigations on the site, it is highly considered that the prevailing conditions at the proposed site are generally favourable for the structural elements of the development, provided the recommendations given in this report are adhered to.
. The ground conditions described in this report refer specifically to those encountered in the trial pits and adjacent exposure localities. It is therefore quite possible that variance conditions with those discussed above should be expected elsewhere on site.
. In shallow cuts or where the road levels are close to the natural ground, the pavement can be subjected to swell movements of the order of 20-30mm or collapse settlements of similar magnitude except under the embankments where these can increase to levels of between 50-100mm. Most of these movements can be differential because of the non-uniform nature of the problem soils. In addition, the potentially collapsible hillwash should be typified either with heavy vibratory rollers when thin or impact roller.
. Appropriate surface and subsurface drainages will be required (especially in the cut areas) in order to prevent the development of perched water tables existing under the road. Cut slopes require protection due to the presence of the highly erodible micaceous granites. Strict geotechnical supervision will be required during the construction phase.
Detailed Design of the Midrand K109 Road Project Page: 44 Site Geotechnical Investigations Report
. Roadlab acknowledges that the information contained in this report can be used for urban planning, construction costing and detailed architectural/structural design. However, a detailed geotechnical site investigation incorporating boring, trenching and specific foundation investigations may be carried out for specific purposes.
Detailed Design of the Midrand K109 Road Project Page: 45 Site Geotechnical Investigations Report
REFERENCES
Vermeulen, N; Wardle, G; Berry, A; Parrock, A; Vorster, E; Davis, G; Heymann, G; Grabe, H; Stiff, J; Day, P; Modishane, T; Pape, T; (2010); Site Investigations Code of Practice; The South African Institute of Civil Engineering; pp57
Fakir, S; Broomhall, L; (1999); Midrand State of the Environment Report; World Conversation Union; pp84
Detailed Design of the Midrand K109 Road Project Page: 0 Site Geotechnical Investigations Report
Appendix A
Midrand K109 Road Project
Detailed Design of the Midrand K109 Road Page A-0 Geotechnical Investigations
Appendix A_1 Drawing GRP02/21/1Ply: Sheet 1 of 8-Preliminary Design of the K109 Road from Kaalfontein to K54 Layout and Services Plan from Stations 3.1 to 4.7km [Scale: 1:1,000]
Detailed Design of the Midrand K109 Road Project Page: A-1 Site Geotechnical Investigations Report
Appendix A_2 Drawing GRP02/21/2Ply: Sheet 2 of 8-Preliminary Design of the K109 Road from Kaalfontein to K54 Layout and Services Plan from Stations 4.0 to 5.7km [Scale: 1:1,000]
Detailed Design of the Midrand K109 Road Project Page: A-2 Site Geotechnical Investigations Report
Appendix A_3 Drawing GRP02/21/3Ply: Sheet 3 of 8Preliminary Design of the K109 Road from Kaalfontein to K54 Layout and Services Plan from Stations 5.7 to 7.4km [Scale: 1:1,000]
Detailed Design of the Midrand K109 Road Project Page: A-3 Site Geotechnical Investigations Report
Appendix A_4 Drawing GRP02/21/4Ply: Sheet 4 of 8-Preliminary Design of the K109 Road from Kaalfontein to K54 Layout and Services Plan from Stations 7.4 to 9.1km [Scale: 1:1,000]