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SITE SELECTION STUDY FOR

PROPOSED NEW TRANSMISSION

SUBSTATION IN THE ESKOM

NORTH EASTERN REGION

GEOTECHNICAL REPORT

PRELIMINARY GEOTECHNICAL INVESTIGATION FOR THE

SELECTION OF A SITE FOR THE PROPOSED NEW WOLWEKRAAL

SUBSTATION

February 2010

*(27(&+1,&$/,19(67,*$7,216 64#05/+55+106'%*01.1);


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CONTENTS

1.0 INTRODUCTION

2.0 THE NATURE OF THE PROJECT

3.0 OBJECTIVES OF INVESTIGATION

4.0 LOCALITY OF STUDY AREAS

5.0 DESK STUDY

5.1 Maps Consulted

5.2 Aerial Photographic Interpretation

5.3 Review of Desk Study and Selection of Sites

5.4 Seismic Zoning

6.0 REGIONAL ENVIRONMENT

6.1 Geography

6.1.1 Topography and Drainage6.1.2 Flood Line6.1.3 Climate

6.2 Geology

6.3 Water Table

7.0 SITE INVESTIGATION

7.1

Topographical Survey7.2 Geometric Design

7.3 Exploratory Work

7.4 Laboratory Testing

8.0 GEOTECHNICAL EVALUATION

8.1 Site-I and II

8.2 Site-III

8.3 Water Table

8.4 Topography - Preliminary Substation Positioning, Geometry

(Earthworks Volumes) and Access Roads

8.5 Flood-Line Studies

9.0 CONCLUSIONS AND RECOMMENDATIONS

10.0 REFERENCES


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APPENDICES

A Flood Line Studies

B Test Pit Profiles

C Laboratory Test Results

D Contour Plans, Preliminary Geometric Designs and Sections


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TITLE :GEOTECHNICAL REPORT

PRELIMINARY GEOTECHNICAL INVESTIGATION FOR THESELECTION OF SITES FOR THE PROPOSED NEW WOLWEKRAAL

SUBSTATION

PREPARED BY: Geotechnical InvestigationsTransmission Technology

CLIENT : Land and RightsTransmission

PROJECT TEAM: F A GrovDr Johan LourensP GreybeD AngoveTyris Plant HireSoillab

REPORT NO: GR02-2010

DATE : February 2010

Approved :

F A Grov

Senior Specialist ConsultantGeotechnical Investigations


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1.0 INTRODUCTION

Eskom plans to construct a new 400/132 kV Substation near Marble Hall in the North Eastern

Region (Mpumalanga). (TheHighveld North and Lowveld Northwest Project)

A Site for the planned development is urgently required in the area near Marble Hall. The firstphase of this investigation included extensive desk studies, where a total number of three most

suitable sites were identified for the substation. For the selection of these possible sites during

the desk study, factors such as the geology, topography, farming activities, mining activities,

Eskom installations and power line servitude routes were considered. It should be noted that

options for suitable sites are limited in the Marble Hall area due to intensive irrigation farming

activities.

Information collected during this investigation is suitable for site selection purposes, and

once the final design is required, a Detailed Geotechnical Investigation will be required to

provide design parameters and confirm findings of this investigation..

2.0 THE NATURE OF PROJECT

The project comprises the construction of a Substation in the Marble Hall area (Mpumalanga).

The development would include the installation of typical equipment such as:

Electrical transformers Circuit breakers or line termination structures High-voltage switchgear Low voltage switchgear Surge & lightning protection equipment Control and metering equipment Access roads and buildings

3.0 OBJECTIVES OF INVESTIGATION

The objectives of this investigation were defined as follows:

- Conduct intensive desk studies of the area to identify a total number of three mostsuitable sites for the proposed new substation

- Obtain geotechnical information during a Preliminary Geotechnical Investigation ofeach selected site to confirm findings of the desk study for suitability evaluation of

sites

4.0 LOCALITY OF STUDY AREAS FOR PROPOSED NEW SUBSTATION

It was requested by System Planning Transmission, to find a suitable site for this substation

within a radius of 10km from the coordinate of the existing substation

S 25 00 19.7 E 29 18 9.63

Three most suitable areas were identified, namely, Site-I; Site-II and Site-III, and are located

at:

Site-I S 25 04 24 E 29 16` 57

Site-II S 25 04 12 E 29 17` 24

Site-III S 25 05 16 E 29 18` 08


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LOCALITY OF SITES FIGURE-I

5.0 DESK STUDY

5.1 Maps Consulted

An attempt was made to collect as much information as possible of the study area

demarcated by Transmission System Planning, for the proposed new substation

during the desk study. For this purpose the following maps were consulted:

i)`Topographical Maps 2429CD Marble Hall; 2529AB Groblersdal;

2529AA Siyabuswa; 2429CC Rathoke

ii) Ortho Photos Covering the area within a 10km radius from the existing

Substation

iii) Geological Maps 2528 Pretoria ; 2428 Nylstroom

iv) Mineral Map - Mineral Map of the Bushveld Complex South Africa

With Special reference to Platinum and Chrome

v) Mining - Simplified Geology, Selected Mines and Mineral Deposits South

Africa, Lesotho and Swaziland

5.2 Aerial Photographic Interpretation

In principle the following features are being studied, information being obtained and

interpreted when studying aerial photographs for geotechnical purposes:

- Reflection of the action of nature in creating the existing conditions

- Grouping of materials according to certain patterns

- Definition of various boundaries and linear features of

significance

- Field checking by visual inspection

Stereo-interpretation has a great advantage over interpretation of a single photograph,because it is better able to identify topographical and erosion features, grey tones, and

textures have greater requisite clarity contrasts. Basically, two aspects of the air photo


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image are revealed in the stereo-model of a given area, and these are surface form and

grey tone, which could be subdivided as:

a) Elements of Surface Form

- Topographic form

- Drainage form

- Erosion form

b) Elements of Grey tone and Texture of :

- vegetation

- due to land use

- soil and rock material

Geotechnical information obtained in this way was correlated with Geological Map

data.

5.3 Review of Desk Study and Selection of Sites

The final electrical design of the substations was not finalised at the time of this

investigation and it was proposed by the electrical designers to use an area of 400 x

400m for the proposed platform. Initially the desk study was performed to identify

sites of 600m x 600m. The area for suitable sites is limited due to the presence of

dolomite and the densely developed irrigation scheme in the area of study.

For the purpose of the evaluation study, three sites were identified during the desk

study, taking into account present Eskom installations, geology, established

developments and geographical constraints.

5.4 Seismic Zoning

The South African loading code, SANS 10160 1969 (Figure-IIa and IIb) , shows

that the proposed sites for this study are situated in an area where the peak groundacceleration with a 10% probability of being exceeded in a 50 year period is less than

50cm/sec. Figure-IIb also shows the zones where detailed seismic design (Zone-I)

SEISMIC HAZARD MAP OF SA FIGURE-IIa

Wolwekraal SS


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SEISMIC HAZARD ZONES OF SA FIGURE-IIb

and compliance with minimum requirements (Zone-II) are specified by the code. Theproposed Wolwekraal sites fall outside of these Zones.

Wolwekraal Sites


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More recent data produced by the Council of Geoscience place the sites within the

zone where the minimum seismic event, with a 10% probability of being exceeded in

a 50 year period, falls in the range of 0,07g to 0,09g (Figure-III). This data however,

still needs to be verified.

6.0 REGIONAL ENVIRONMENT

6.1 Geography

6.1.1 Topography and Drainage

The three sites selected for evaluation purposes are located within a 1 km radius and

are considered to be subject to the same regional topographic and drainage influences

(See appendix-A).

Site-I and II are located on the northern slopes of the same hill and Site-III is on

the ridge of the hill. The topography of the three sites forms part of the regional flat

topography, with slopes traversing Site-I (1,5%) and Site-II (1,2%) from south to

north. Site-III is traversed in no definite pattern with flat slopes of the order of2%.

Site-I and Site-II drains to the north into a vlei area. The Sites are located on portions

of the farm Loskop Noord.

6.1.2 Flood line

Flood line studies carried out favours Site-III, having the least slopes and run-offs,

with no watercourse near the site. Site-I is largely affected by the irrigation scheme of

the region, which will require major irrigation channels to be diverted and Site-II is a

risk with regards to the 1:50year flood line.(See Appendix-A)

6.1.3 Climate

N-Value

The "Weinert N-Value", that describes the climatic environment, is approximately 4

for the area. Where "N" is more than "5", disintegration is the prominent form of

weathering, and where "N" is less than "5", decomposition affects those rocks

whose minerals are liable to change chemically under atmospheric conditions.

Rainfall

This is a summer rainfall region and the average yearly rainfall is 577 mm.

. Vegetation

Sites-I and II are covered with crops and irrigation channels are traversing thesesites. Site-III is covered with medium to dense indigenous grass and bush.

6.2 Geology

All three sites are underlain by medium grained Nebo Granite of the Bushveld

Complex and Granite-Gneiss.

6.3 Water Table

A shallow perched water table is present on Site-I and Site-II


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7.0 THE INVESTIGATION

7.1 Topographical Survey

Topographical surveys of sites were carried out to enable preliminary geometric

designs, which forms an important part of the geotechnical evaluation of sites.

7.2 Geometric Design

Since the power line routes had not been fixed at the time of this investigation,

geometric designs were carried out merely to obtain an idea of volumes of earthworks

that could be expected at each site.

7.3 Exploratory Work

Site-I and II

The above sites are subject to similar constraints, re densely cultivated and traversed

by irrigation waterlines in all directions. Test pits were excavated randomly with aTLB (Cat 416) to confirm findings of the desk study. The Granite Gneiss was found

deeply weathered due to the apparent flat topography which resulted in poor

drainage of both sites.

It was found that the test pits were mostly water logged near surface and thus not

suitable for the construction of an earth platform.

Site-III

Test pits were excavated randomly to confirm findings of the desk study.

The profile showed relatively shallow weathering down to anticipated depths of theconstruction of an earth platform. It is well known that this material is of excellent

quality for the construction of the earth platform for the substation.

7.4 Laboratory Testing

Laboratory tests on soil samples were primarily conducted to determine Geotechnical

properties of the soil, confirming findings of the desk study.

The following tests were carried out:

- Grading (Mechanical and Hydrometer)

- Atterberg Limits

- Moisture Content

- Electrical Conductivity

8.0 GEOTECHNICAL EVALUATION

8.1 Site-I and II

The soil profile of the above sites is similar. Laboratory testing confirmed geotechnical

properties and findings during profiling of test pits.

Climatic factors have combined to create a mode of decomposition characterised by

chemical disintegration of the profile. Therefore, the Granite/ Gneiss have decomposed down

to depths ofat least 1,5 to 2,0 m. The Granite Gneiss, due to its composition, resisted these

climatic factors to a fair extend with depth, limiting decomposition to these shallow depths.


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Geology Influences on Construction

It is believed that the ground conditions of the above sites would have a great affect on

conventional construction methods. De-watering and diverting all irrigation channels of the

areas will be required prior to any construction taking place. Provision for flooding during

construction will also be required which might turn out to be highly costly. This could result inyears delay of the construction of the substation, since careful irrigation studies will be

required not to disturbed the integrated irrigation system of the region.

Though the material properties have been changed drastically (reworked/residual material),

most of the materials are considered suitable for civil construction.

8.2 Site-III

The granite profile show to be extremely less weathered than the profiles of Sites-I and II.

The material found on this site is considered an excellent material for the construction of a

substation platform. Inspection of the existing quarry on the property and test pits excavated

confirms the soil profile to be uniform present over area. Laboratory test results confirmed the

findings during profiling test pits.

Geology Influences on Construction

The soil profiles proved that materials from this site are of an excellent construction quality.

8.3 Water Table

There is a shallow perched water tablepresent on Site-I and Site-II, which would result in

major design measures to be taken. It is anticipated that this will result in a highly costly

exercise.

8.4 Topography - Preliminary Substation Positioning, Geometry (Earthworks

Volumes) and Access Roads

An attempt was made to position and simulate platforms for each site.

Topographical features and present soil information of each site were taken into account

during this exercise. The following volumes for earthworks were obtained during this exercise

for each site:

Site Strip m Cut m Fill m Special Measures

Site-I 25 215 23 640 18 215 De-watering import fill

Rerouting Regional IrrigationSite-II 25 215 23 250 21 130 De-watering import fill

Rerouting Regional Irrigation

Site-III 25 215 38 200 37 000 None

All three sites are accessed rather easily, with similar lengths of access roads to be

constructed.

Attached to this report are preliminary geometric designs, indicating optimised platform

positioning for each site (Appendix-C).


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8.5 Flood Line Studies

Flood line studies have revealed that Sites-I and II are not suitable for this development. Site-I

will require major construction measures to divert irrigation channels which will have an effect

on the region, Site-II has a risk of being flooded during a 1: 50 year flood.

9.0 CONCLUSIONS AND RECOMMENDATIONS

Considering the results of all the studies carried out during this investigation it is clear that

Site-III is recommended as the suitable site. Sites-I and II are not considered suitable.


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10.0 REFERENCES

10.1 Jennings Brink & Williams (1973). Revised Guide to Soil Profiling for Civil

Engineering purposes in South Africa. The civil Engineer in S.A. Jan. 1973.

10.2 Site Selection Desk Studies Dr J Lourens

10.3 Flood-line Studies Peter Greybe February 2010-03-04


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APPENDIX-A

Flood line Studies

Wolwekraal


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