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Jeffares & Green (Pty) Ltd ESKOM

W:\Earth Sciences\2518 - Various Geotechnical Investigations for Eskom (CC)\62 – Jericho SS

JERICHO TELECOMMUNICATION TOWER

GEOTECHNICAL REPORT

CONTENTS

1. INTRODUCTION ....................................................................................................... 1

2. APPOINTMENT ......................................................................................................... 1

2.1. Information Available .......................................................................................... 1

3. SITE LOCATION ....................................................................................................... 1

3.1. Topography and Drainage .................................................................................. 3

3.2. Vegetation, Land Use and Existing Infrastructure ............................................ 3

3.3. Access ................................................................................................................. 3

4. GEOLOGY ................................................................................................................ 3

5. CLIMATE ................................................................................................................... 4

6. FIELDWORK ............................................................................................................. 4

6.1. Trial Pits ............................................................................................................... 4

6.2. DCP Tests ............................................................................................................ 5

7. LABORATORY TESTING ......................................................................................... 5

8. GENERAL ASSESSMENT OF THE TOWER SITE ................................................... 6

8.1. Ground Conditions.............................................................................................. 6 8.1.1. Fill ............................................................................................................... 6 8.1.2. Colluvial soil ............................................................................................... 6 8.1.3. Pebble marker ............................................................................................ 6 8.1.4. Residual granite ......................................................................................... 6

8.2. Groundwater ........................................................................................................ 6

8.3. Expansive, Collapsible and Dispersive soils .................................................... 6

9. RECOMMENDATIONS ............................................................................................. 6

9.1. Foundations ........................................................................................................ 7

9.2. Drainage ............................................................................................................... 8

9.3. Cut and Fill Design .............................................................................................. 8

9.4. Ease of Excavation ............................................................................................. 8

9.5. Trench Stability ................................................................................................... 8

10. CONCLUSIONS ........................................................................................................ 9

11. REFERENCES ........................................................................................................ 10

APPENDIX A: TRIAL PIT LOG & PHOTOGRAPH ............................................................. i

APPENDIX B: DCP TEST RESULTS ................................................................................ iii

APPENDIX C: SITE PHOTOGRAPHS ............................................................................... v


W:\Earth Sciences\2518 - Various Geotechnical Investigations for Eskom (CC)\62 – Jericho SS

APPENDIX D: LABORATORY RESULTS ....................................................................... vii


2518/62 1 Jericho SS Geotechnical Investigation Report January 2014

JERICHO SS TELECOMMUNICATION TOWER

GEOTECHNICAL REPORT

1. INTRODUCTION This report presents the results of a geotechnical investigation undertaken for the proposed construction of a communication tower at the Eskom Jericho Substation (SS). The site is located approximately 50 km east of Ermelo in the Mpumalanga Province of South Africa. The objectives of the investigation are to assess the suitability of the site from a geotechnical perspective, provide an overview of the founding conditions for the proposed tower, identify the presence of problematic ground conditions, assess the excavation conditions for earthworks and assess the suitability of the in-situ materials for use during construction. The field investigation was carried out on the 10th of December 2013 and entailed the following:

The excavation of one trial pit

The execution of one dynamic cone penetrometer test

The retrieval of one disturbed sample for laboratory testing It is recommended that the foundation excavations are inspected during construction by a competent person prior to casting any concrete in order to verify the assumptions made in this report. Should conditions at variance from those described in this report be encountered, then the services of a geotechnical professional must be sought. 2. APPOINTMENT The Task Order was received from Eskom on the 21st of November 2013, order number 3070161030.

2.1. Information Available

The exact tower position was indicated to the Jeffares and Green Engineering Geologist by Eskom’s Mr Mboneni Ngwenyama prior to the commencement of the investigation. The trial pit (TP) was executed directly on the footprint of the proposed tower, as can be seen in Figure 3 overleaf. In the purchase order it is indicated that a 21 m tower is to be erected, installed with a 1.8 m diameter parabolic antenna at 21 m height.

3. SITE LOCATION The Jericho SS is accessed via a paved road off the R65 heading east from Ermelo in the Mpumalanga Province of South Africa. The locality plans and site layout plan can be seen in Figures 1 through 3, overleaf.



Figure 1: Locality Plan – Small scale

Figure 2: Locality Plan – Large scale



Figure 3: Site Plan

3.1. Topography and Drainage

The topography of the surrounding area is generally flat. The Jericho Dam wall is approximately 100 m to the north west, as can be seen above on Figure 3: Site Plan. No drainage features were observed in the immediate vicinity of the site.

3.2. Vegetation, Land Use and Existing Infrastructure

This investigation area falls within the Jericho Dam’s development area where a variety of infrastructure and developments are present. However, the excavation of the trial pit was done through fill material for the first 300 mm; where after natural ground was encountered. The area falls under the “Mesic Highveld Grassland Bioregion” which can be described as grassland. The proposed tower position does not fall within the substation grounds, as can be seen from the photographs give in Appendix C.

3.3. Access

The site is easily accessible using a paved road from the south. However, during the wetter summer months, rainfall can soften the surface soils that can lead to difficult driving conditions.

4. GEOLOGY According to the 1:250 000 scale Geological Map 2630 Mbabane, the site is underlain by the porphyritic (describes a rock texture consisting of larger mineral grains in a finer matrix) leucocratic (light coloured) biotite granite from the Anhalt Granitoid Suite from the Basement Complex and is from the Archean Age. The regional geology of the proposed tower position and the surrounding area can be seen in Figure 4.



Figure 4: Geological map

Symbol Stratigraphy Lithology

Anhalt Granitoid Suite, Basement Complex

Leucocratic biotite granite, porphyritic

5. CLIMATE The climatic regime plays a fundamental role in the development of a soil profile. Weinert (1964) demonstrated that mechanical disintegration is the predominant mode of rock weathering in areas where his climatic “N-value” is greater than 5, while chemical decomposition predominates where the N-value is less than 5. Weinert’s climatic N-value for the study area is approximately 2.5. This implies that chemical decomposition is the dominant mode of weathering at this site. 6. FIELDWORK The fieldwork was undertaken on the 10th of December 2013 in the middle of the wetter, summer season.

6.1. Trial Pits

One trial pit (TP) was excavated on the proposed tower footprint. The trial pit was excavated by hand to a depth of 1.50 m, and advanced to a depth of 1.85 m by means of a hand auger. The trial pit was profiled immediately after excavation by our Engineering Geologist and photographed. The trial pit profile and photographs are contained in Appendix A.

Extracted from 1:250 000 scale Geological Map 2630 Mbabane. Council for Geoscience



6.2. DCP Tests

One in-situ Dynamic Cone Penetrometer (DCP) test was carried out prior to the excavation of the trial pit on the proposed tower footprint. The DCP test was undertaken from the natural ground level (ngl) to a depth of 3.00 m. No refusal occurred. The results have been used to derive, empirically, Estimated Allowable Safe Bearing Pressures (EASBP) for the soils. The estimation of the EASBPs is based on shear strengths, obtained using empirical methods from the DCP test results. The interpretation of the DCP test results must take into account the condition of the soil profile through which the probe is advanced. Based on the trial pit profile, the DCP test was advanced through mostly sandy clays, and therefore a cohesive soil profile is assumed for the interpretation of the DCP results. The DCP test results indicate these soils will have approximate EASBPs of between 60 – 80 kPa. The moisture content of the soil, as well as any gravel, concretions, or boulders in the soil profile affect the results of a DCP test. As can be seen from the results, the EASBPs at depths where the pebble marker is encountered are higher, possibly due to the gravel in the horizon. Furthermore, a wet soil horizon will provide lower consistencies than a similar test undertaken during the drier season, as percolating water softens the subsoils. Moisture content should thus always be noted and made mention of in any DCP investigation. The DCP test was undertaken on soil that was observed to have a “very moist” moisture content. As such the DCP test results are thought to be an accurate reflection of the soil strength. Estimation of EASBPs from DCP probes in gravelly soils may also be unreliable, and unrealistically high EASBPs may be obtained, due to the apparatus striking gravel, concretions or boulders. The DCP test result is given in Appendix B.

7. LABORATORY TESTING One disturbed sample was recovered from the residual granitic soil and submitted for foundation indicator tests, which comprised sieve and hydrometer analysis and Atterberg Limit testing. The test results are summarized in Table 1 and the full results are included in Appendix D:

Table 1: Grading and Atterberg Limit Determinations

Pit No

Depth (m)

Description Particle Size (%)

Atterberg Limits (%) Heave

Potential Clay Silt Sand Gravel LL PI LS

TP 1.00 – 1.20 Sandy CLAY 27 19 50 4 31 12 6 Low

LL- Liquid Limit PI - Plasticity Index LS - Linear Shrinkage

The results of the soil grading test indicate that although the soil consists predominately of sand, the sample contained a significant amount of clay. It is therefore recommended that the soil be classified as cohesive for engineering evaluation purposes.



The potential for heave related movement of the soil sample was assessed according to the Van der Merwe method of predicting potential heave (Williams and Donaldson 1980). This estimates the expansiveness from the equivalent Plasticity Index of the whole sample and the clay content of the whole sample. The laboratory test results indicate that the soils have a “low” potential for expansiveness. Significant moisture related heave and shrinkage for this soil are therefore not expected under fluctuating soil moisture conditions. 8. GENERAL ASSESSMENT OF THE TOWER SITE From a geotechnical perspective the site is suitable for the construction of a communication tower, provided that the recommendations given in this report are implemented, in order to mitigate potential geotechnical constraints.

8.1. Ground Conditions

The ground conditions at the site are described from the observations in the trial pit, the results of the DCP test and the results of the laboratory tests. It must be noted that the investigation was undertaken during the wetter summer period, and persistent light rain had been falling for approximately a week prior and during the investigation.

8.1.1. Fill

Extensive development has been undertaken in the vicinity of the proposed tower. A fill layer of loose, clayey silty fine sand was encountered from 0 – 0.30 m.

8.1.2. Colluvial soil

A hillwash layer encountered from 0.30 – 0.50 m was described as being a very moist, medium dense, intact, clayey silty fine sand.

8.1.3. Pebble marker

A pebble marker is believed to be the interface between transported and residual soils and is usually characterized by coarser material such as a gravel in a matrix of finer material. A pebble marker was encountered from 0.50 – 0.70 m and was described as a loose, intact, clayey silty fine gravelly sand.

8.1.4. Residual granite

Residual granite encountered from 0.70 – 1.80 m was generally described as being soft becoming firm with depth, pinholed, silty sandy clay. Hand auger refusal was reached at 1.85 m on firm, silty sandy clay of residual granite with a relict rock structure.

8.2. Groundwater

Good drainage conditions seemed to be prevalent throughout the profile, as persistent rain did not lead to surface water ponding or ground water seepage, and groundwater is not expected to be problematic at the site.

8.3. Expansive, Collapsible and Dispersive soils

The soils from this region are known to have a collapsible grain structure (Brink, 1985). The residual granite encountered from 0.70 to beyond 1.80 m was voided which is a good indication that the soil could have a collapsible grain structure.

9. RECOMMENDATIONS It is understood that the project involves the construction of a self-supporting lattice-type communication tower. Mr Ngwenyama indicated the proposed tower position to Jeffares and Green’s Engineering Geologist. The purchase order stipulates that a 21 m tower is to be



erected; installed with a load of a 1.80 m diameter parabolic antenna at a 21 m height. Mr Ngwenyama had, on the day of the investigation, relayed information that a 4 x 4 m square platform would possibly be used for the foundation. The foundation must be designed to resist the uplift forces imposed by wind loading on the tower itself and also on the 1.80 m diameter parabolic antenna. For the purpose of this report, it is assumed that the maximum foundation load will not exceed 150 kPa. The bearing pressures resulting from wind loading will be significantly higher that the bearing pressure imposed by the tower itself and this must be taken into account during the tower design.

9.1. Foundations

Residual soils developed from the Basement Complex Granites are known to be potentially problematic founding materials. These residual granite soils are frequently collapsible (Brink, 1985). For collapse settlement to occur, all of the following conditions must be satisfied:

The soil must have a collapsible fabric.

An initial condition of partial saturation must be present.

An increase to moisture content must occur.

An imposed pressure greater than the existent overburden pressure must be applied.

The residual soils exhibited a pinholed structure, which is an indication of a potentially collapsible fabric and these soils should therefore be considered collapsible. The soils throughout the profile were typically described as having a soft to firm consistency. Based on the DCP test results the Estimated Allowable Safe Bearing Pressure for these soils to a depth of approximately 3.00 m below ngl are in the order of 60 – 80 kPa. Due to the potentially collapsible soil fabric and the EASBPs being significantly lower than the expected foundation loads, neither the colluvial nor the residual soils are suitable founding materials. It is recommended that the tower is founded on an engineered soil raft. The poor quality soils beneath each foundation footprint should be removed to a minimum depth of 1.50 m below the base of the foundation level and replaced in layers with properly compacted imported fill material of suitable quality to support the foundation slab. The foundations loads must be limited to a maximum of 150 kPa for design purposes. For the foundation specifications detailed above, the following soil raft design is recommended:

Minimum dimensions: 1.50 m larger than footing diameter

Material Specification: G5 (According to TRH14 materials classification)

Minimum compaction: 95% of Modified AASHTO maximum dry density at Optimum Moisture Content

Should the foundation specifications vary from those detailed above then a review of the soil raft design will be required. Strict monitoring of soil raft construction should be undertaken to ensure that the design specifications outlined in this report are met.



Alternatively, a piled foundation option may be considered. Due to the high establishment costs associated with pilling equipment, this foundation method is likely to be expensive. Should piling be considered feasible, it is recommended that further investigations are undertaken to determine the ground conditions with depth. The foundation conditions must be inspected during construction by a competent person prior to casting any concrete. Should conditions at variance from those described in this report be encountered, then the services of a geotechnical professional must be sought.

9.2. Drainage

It is recommended that site drainage and landscaping is implemented, as is good engineering practice. This must also include the conveyance of all runoff away from the tower foundations and off the site. These soils could be potentially collapsible and as such water should be kept away from foundations.

9.3. Cut and Fill Design

All earthworks must be carried out in accordance with SANS 1200 (or current version).

9.4. Ease of Excavation

According to the criteria published in SANS 1200D Earthworks, as specified for restricted excavation (shown in Table 2), soft excavations conditions are expected to a depth of 3.00 m below ngl. As is the nature of these granites derived from the Basement Complex, possible corestones and Boulder (excavation class A) conditions may be encountered during construction. Table 2: SANS 1200D excavation class descriptions – restricted excavation Excavation Class Description

Soft

Excavation in material that can be efficiently removed by a back-

acting excavator of flywheel power approximately 0.10 kW per

millimetre of tined-bucket width, without the use of pneumatic tools

such as paving breakers

Intermediate Excavation in material that requires a back-acting excavator of

flywheel power exceeding 0.10 kW per millimetre of tined-bucket width

or the use of pneumatic tools before removal by equipment equivalent

to that specified for soft excavation.

Hard Hard rock excavation shall be excavation in material (excluding

boulder excavation) that cannot be efficiently removed without blasting

or wedging and splitting.

Boulder (excavation

class A)

Excavation in material containing more than 40% by volume of

boulders of size in the range of 0.03 - 20m3, in a matrix of soft or

smaller boulders.

9.5. Trench Stability

The soils are not expected to be unstable, but the risk of excavation collapse will have to be assessed on site during construction and shoring must be implemented if considered necessary. It is recommended that the Contractor appoints a competent excavation supervisor in terms of Section 11 of the Construction Regulations 2003 if excavations are undertaken during construction.



10. CONCLUSIONS The geotechnical investigation undertaken indicates that the site is suitable for the construction of the proposed communication tower, from a geotechnical perspective, provided that the recommendations given in this report are implemented.

The geology consists of soils derived from granite rock of the Anhalt Granitoid Suite, Basement Complex. These soils are known to be potentially collapsible.

Soils exhibiting collapsible characteristics were encountered between 0.70 – 1.80 m and soils with low bearing capacities were encountered to a depth of 3.00 m below ngl. These soils are therefore unsuitable founding materials.

It is recommended that the tower is founded on an engineered soil raft. The specifications for the soil raft are outlined in this report.

The presence of core stones may become problematic during excavation.

It is essential that water be diverted away from foundations at the site.

Groundwater seepage was not observed in the trial pit and shallow groundwater conditions are not expected to be problematic at the site.



11. REFERENCES 1. Brink, A.B.A. (1985). Engineering Geology of South Africa Volume 1. Building

Publications Pretoria. 2. Core Logging Committee of the South African Section of the Association of Engineering

Geologists (1976). A Guide to Core Logging for Rock Engineering. Proceedings of the Symposium on Exploration for Rock Engineering, Johannesburg.

3. Jennings, J.E., Brink, A.B.A. and Williams, A.A.B. (1973). Revised Guide to Soil Profiling

for Civil Engineering Purposes in Southern Africa. Transactions of the South African Institution of Civil Engineers, Vol. 15.

4. Johnson, M.R., Anhausser, C.R., Thomas, R.J. (1996). The Geology of South Africa. The

Geological Society of South Africa and the Council for Geoscience. 5. Williams, A.A.B. & Donaldson, G. (1980). Building on Expansive Soils in South Africa.

Expansive Soils of the 4th International Conference on Expansive Soils, June 16-18, 1980, Denver, Colorado, American Society of Civil Engineers, 2, 834-844.


2518/62 i Jericho SS Geotechnical Investigation Report January 2014

APPENDIX A: TRIAL PIT LOG & PHOTOGRAPH


2518/62 i Jericho SS Geotechnical Investigation Report January 2014


2518/62 ii Jericho SS Geotechnical Investigation Report January 2014

Photograph 1: Trial pit profile

Photograph 2: Firm residual granite with relict rock structure recovered 1.80 – 1.85 m.


2518/62 iii Jericho SS Geotechnical Investigation Report January 2014

APPENDIX B: DCP TEST RESULTS


2518/62 iv Jericho SS Geotechnical Investigation Report January 2014


2518/62 v Jericho SS Geotechnical Investigation Report January 2014

APPENDIX C: SITE PHOTOGRAPHS


2518/62 vi Jericho SS Geotechnical Investigation Report January 2014

Photograph 3: Location of proposed tower, next to the existing substation looking in a southern direction.

Photograph 4: Investigation area, looking in a south eastern direction with the existing Eskom Jericho Substation in the background.


2518/62 vii Jericho SS Geotechnical Investigation Report January 2014

APPENDIX D: LABORATORY RESULTS


2518/62 viii Jericho SS Geotechnical Investigation Report January 2014

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