University of Fort Hare, Alice Campus Geotechnical Investigation COMPILED FOR: MBB Consulting Engineers P O Box 509 Grahamstown 6140 Telephone: +27 (0)46 622 7223 Facsimile: +27 (0)86 570 7844 COMPILED BY: WorleyParsons RSA (Pty) Ltd ABN 61 001 279 812 Contact person: Carol White 57 Jarvis Road Berea 5241 PO Box 19829, Tecoma 5205 South Africa Telephone: +27 (0)43 721 1502 Facsimile: +27 (0)43 721 1535 email: Carol.White@worleyparsons.com www.worleyparsons.com Copyright 2013 WorleyParsons RSA (Pty) Ltd
Disclaimer This report has been prepared on behalf of and for the exclusive use of MBB Consulting Engineers, and is subject to and issued in accordance with the agreement between MBB Consulting Engineers and WorleyParsons RSA (Pty) Ltd. WorleyParsons RSA (Pty) Ltd accepts no liability or responsibility whatsoever for it in respect of any use of or reliance upon this report by any third party. Copying this report without the permission of MBB Consulting Engineers and WorleyParsons RSA (Pty) Ltd is not permitted. PROJECT 280090 - REV DESCRIPTION ORIG REVIEW WORLEY- PARSONS APPROVAL DATE CLIENT APPROVAL DATE A Preliminary Ms C White Ms A Burger Dr GV Price 2013-08-11 N/A Page i
CONTENTS 1. INTRODUCTION... 1 1.1 GENERAL... 1 1.2 WORLEYPARSONS PROPOSAL... 1 1.3 AIM OF THIS REPORT... 1 1.4 STRUCTURE OF THIS REPORT... 2 2. METHOD OF INVESTIGATION... 3 3. SITE DESCRIPTION... 4 4. GEOLOGY... 6 5. FIELD TESTING... 8 5.1 TRIAL HOLE INVESTIGATIONS... 8 5.2 DYNAMIC CONE PENETRATION TESTING... 18 6. LABORATORY TESTING... 20 6.1 INTRODUCTION... 20 6.2 TEST RESULTS... 20 7. GEOTECHNICAL APPRAISAL... 22 7.1 INTRODUCTION... 22 7.2 ENGINEERING GEOLOGY... 22 7.3 STRUCTURE FOUNDATIONS... 22 7.4 GEOTECHNICAL RECOMMENDATIONS... 23 APPENDIX 1 - TRIAL HOLE LOGS APPENDIX 2 DCP TEST RESULTS APPENDIX 3 LABORATORY TEST RESULTS Page ii
1. INTRODUCTION 1.1 GENERAL WorleyParsons RSA (Pty) Ltd was, on 10 July 2013, appointed by MBB Consulting Services (EC) (Pty) Ltd, to undertake a geotechnical investigation at the proposed new residences for the University of Fort Hare, Alice campus in Alice, Eastern Cape. This after Ms A Burger of WorleyParsons RSA (Pty) Ltd had, on 04 July 2013 provided Mr P Ellis of MBB Consulting Engineers with a methodology proposal and cost for the geotechnical investigation. The geotechnical investigation would ascertain the foundation conditions available at the new building site and provide recommendations regarding founding depths for the new structure. 1.2 WORLEYPARSONS PROPOSAL WorleyParsons proposed, on recommendation of the client, that the geotechnical investigations would proceed as follows: Field investigations comprising excavation of 19 trial holes at the site The trial holes would be excavated using a TLB Removal of disturbed samples for laboratory testing Profiling of trial holes using the method of Jennings et al with presentation using DotPlot Laboratory testing would comprise of: 9X Foundation Indicator tests including Grading; Atterberg Limits and Hydrometer analyses to determine the engineering characteristics of the unconsolidated materials, and propensity or otherwise for heave and shrinkage 1X MOD AASHTO density and CBR strength tests to determine efficacy of these materials for constructions of roads and/ or platforms at the site 3X Point Load Strength Index (PLSI) to determine strength of the foundation rock and via conversion to Unconfined Compressive Strength (UCS) the Estimated Safe Allowable Bearing Pressure (EASBP) 19X 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, and quality/ density of in situ materials. 1.3 AIM OF THIS REPORT The investigation is aimed at making an assessment of the available founding conditions at the site, with recommendations regarding suitable founding levels for the proposed new two/ three storey residence buildings. Page 1
1.4 STRUCTURE OF THIS REPORT The structure and content of the report continues as follows: Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Method of Investigation Site Description Geology Field Testing Laboratory Testing Geotechnical Appraisal Page 2
2. METHOD OF INVESTIGATION Investigations consisted of an initial desk top study reviewing geological and topographical data with the study area demarcated on geological and topographical maps. WorleyParsons established on site for field investigations on 15 July 2013, with investigations completed the following day. Ms C White and Ms A Burger of WorleyParsons RSA (Pty) Ltd profiled nineteen trial holes excavated by TLB on site, conducted DCP tests at the base of and/ or adjacent to the trial holes, and removed disturbed samples for laboratory testing. From this information a geotechnical report has been compiled outlining the findings of the investigation, with all trial holes presented as appendices in DotPlot Format, along with DCP and laboratory test results. Page 3
3. SITE DESCRIPTION The proposed residences site is situated within the confines of the University of Fort Hare property, located in the town of Alice, within the Eastern Cape Province (Figure 3.1, over page). A portion of the site is an open field directly adjacent to the existing residences, with a water tower and pumpstation centrally sited. An additional portion of the site earmarked for the development, slopes gently in a northerly direction towards a sports ground. Page 4
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4. GEOLOGY The geology of the surrounding area comprises mudstones, siltstones and sandstones of the Balfour Formation, Adelaide Subgroup, Beaufort Group, Karoo Supergroup. The mudstones comprise mostly grey mudstone, sometimes with a high silt component approaching siltstone classification. Sandstone and siltstone occurs within the argillaceous rocks where it is interspersed as individual horizons within the mudstone. Unconsolidated colluvium and alluvium blanket much of the region varying in depth from a few millimetres to several metres. Post-Karoo dolerite dykes and sills are common to the general area, as seen in the presence of a large dolerite sill to the east of the site (Figure 4.1, over page). Page 6
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5. FIELD TESTING 5.1 TRIAL HOLE INVESTIGATIONS A site plan (Figure 5.1, over page) of the new proposed residences was obtained from Mr P Ellis of MBB Consulting who indicated the proposed locations for nineteen trial holes. The trial holes were excavated by TLB on the 15/ 16 July 2013 and have been presented in DotPlot format as individual profiles as Appendix 1. Photos of each trial hole and their GPS co-ordinates are presented below, followed by a generalised profile and unconsolidated soil thickness summary of each in Table 5.1. Plate 1: Trial Hole 1 S 32 47 03.9 E 26 51 13.8 Plate 2: Trial Hole 2 Narrow Face S 32 47 07.5 E 26 51 13.5 Plate 3: Trial Hole 2 Sidewall Page 8
Plate 4: Trial Hole 3 Narrow Face S 32 47 05.6 E 26 51 13.7 Plate 5: Trial Hole 3 Sidewall Plate 6: Trial Hole 4 Narrow Face S 32 47 06.4 E 26 51 13.5 Plate 7: Trial Hole 4 Sidewall Page 9
Plate 8: Trial Hole 5 Narrow Face S 32 47 09.4 E 26 51 12.0 Plate 9: Trial Hole 5 Sidewall Plate 10: Trial Hole 6 Narrow Face S 32 47 11.5 E 26 51 09.6 Plate 11: Trial Hole 6 Sidewall Page 10
Plate 12: Trial Hole 7 Plate 13: Trial Hole 8 S 32 47 09.6 E 26 51 07.4 S 32 47 08.2 E 26 51 07.0 Plate 14: Trial Hole 9 Narrow Face S 32 47 07.6 E 26 51 07.0 Plate 15: Trial Hole 9 Sidewall Page 11
Plate 16: Trial Hole 10 Narrow Face S 32 47 06.3 E 26 51 06.3 Plate 17: Trial Hole 10 Sidewall Plate 18: Trial Hole 11 Narrow Face S 32 47 08.0 E 26 51 03.8 Plate 19: Trial Hole 11 Sidewall Page 12
Plate 20: Trial Hole 12 Narrow Face S 32 47 08.4 E 26 51 02.0 Plate 21: Trial Hole 12 Sidewall Plate 22: Trial Hole 13 Narrow Face S 32 47 08.4 E 26 51 00.8 Plate 23: Trial Hole 13 Sidewall Page 13
Plate 24: Trial Hole 14 Narrow Face S 32 47 09.1 E 26 50 59.6 Plate 25: Trial Hole 14 Sidewall Plate 26: Trial Hole 15 Narrow Face S 32 47 05.8 E 26 51 03.4 Page 14
Plate 27: Trial Hole 16 Narrow Face S 32 47 04.2 E 26 51 04.1 Plate 28: Trial Hole 16 Sidewall Plate 29: Trial Hole 17 Plate 30: Trial Hole 18 S 32 47 02.9 E 26 51 04.1 S 32 47 03.4 E 26 51 05.9 Page 15
Plate 31: Trial Hole 19 Narrow Face S 32 47 03.3 E 26 51 09.4 Plate 32: Trial Hole 19 Sidewall The nineteen Trial Holes on site intersected a relatively consistent profile type but with varying depth to rock/ TLB refusal as determined by individual locations. A generalised profile would be expected as follows: Slightly moist, grey/ dark brown, loose to medium dense, intact SILT: Colluvium overlying Slightly moist, dark/ olive brown, firm/ medium dense, intact/ slickensided, GRAVELLY CLAYEY SILT: Pedogenic Nodular Ferricrete overlying Slightly moist, dark/ olive brown, firm/ medium dense, intact/ slickensided, GRAVELLY CLAYEY SILT: Pedogenic Nodular Ferricrete with rounded gravel and cobbles which have calcified surfaces overlying Slightly moist olive brown, stiff, intact SILTY CLAY: Residual Olive brown, highly to moderately weathered, closely jointed, hard rock: MUDSTONE Individual Trial Hole profiles compiled in DotPlot format are presented as appended, with a Trial Hole Locality Plan shown as Figure 5.1 Depth to rock head is variable with depth to refusal also highly variable as tabulated over page. No groundwater seepage was intersected in any of the Trial Holes. Page 16
Table 5.1: Unconsolidated soil thickness Trial Hole Thickness of Fill (m) Thickness of Colluvium (m) Thickness of Pedogenic Nodular Ferricrete (m) Thickness of soft rock Mudstone/ Siltstone (m) Thickness of medhard rock Mudstone/ Siltstone (m) Depth of Trial Hole (m) TH1-0.15-0.15 0.30 0.70 TH2-0.40 2.30 - - 2.70 TH3-0.26-0.14 0.7 1.20 TH4-0.40 1.30-0.10 1.80 TH5 0.30 0.10 2.40 - - 2.80 TH6 0.4 0.20 1.50 - - 2.10 TH7 0.30-1.60 - - 1.90 TH8 0.15-1.40 - - 1.55 TH9 0.15 1.35 - - 1.50 TH10-0.15 1.05 1.20 TH11-0.40 1.30 - - 1.70 TH12 0.50-1.20 - - 1.70 TH13 0.50 1.30 - - - 1.80 TH14 0.40-1.00 - - 1.40 TH15-0.25 - - 0.25 0.50 TH16 0.08 0.42 1.00 - - 1.50 Page 17
Trial Hole Thickness of Fill (m) Thickness of Colluvium (m) Thickness of Pedogenic Nodular Ferricrete (m) Thickness of soft rock Mudstone/ Siltstone (m) Thickness of medhard rock Mudstone/ Siltstone (m) Depth of Trial Hole (m) TH17-0.60 1.70 - - 2.30 TH18-1.30 1.40 - - 2.70 TH19 0.70-1.20 - - 1.90 Note that Trial holes represent only point sources of information which must be kept in mind when interpreting results: depth to rockhead and TLB refusal may therefore vary, and there should be no interpolation between trial holes. 5.2 DYNAMIC CONE PENETRATION TESTING DCP tests have been undertaken adjacent to/ in most trial holes in order to estimate the bearing capacity of unconsolidated materials and underlying rock. The result of which are attached as Appendix 2. Results indicate high and consistent bearing capacities in most of the trial holes although some have very erratic and unpredictable values. Generally though the site has a good founding regime with respect to bearing capacity for the structures envisaged for the development. DCP values coinciding with the pedogenic layer yields values in excess of 300 kpa increasing with depth where harder pedogenic material is encountered and where bearing capacities can be found to be in excess of 900 kpa. The DCP test results also indicate occasional soft spots within the unconsolidated profile suggesting potential for differential settlement. It is very important to note though that DCP values should only be used for comparative purposes and not as finite standard since dynamic penetration will vary with variations in moisture content. A wet profile will therefore indicate far lower bearing capacity values. Note also that the near-surface silty and sandy materials may in the long term be compressible resulting in differential settlement under load. This too must be taken into consideration when constructing in these materials. Page 18
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6. LABORATORY TESTING 6.1 INTRODUCTION This section of the report presents the findings of laboratory testing as undertaken by Tosca Lab of Port Elizabeth on disturbed samples removed from the site. Test types and the number of tests have been undertaken according to the instructions received from the client on the day of the fieldwork conducted. Major aspects of the testing are indicated in Table 6.2, with the complete set of test results included as Appendix 3. 6.2 TEST RESULTS Laboratory foundation indicator test results are presented in Table 6.2 below. Trial Hole Number Table 6.2 Foundation indicator results Sample Depth (m) Description Equiv. PI % Clay TH2 487/2/FI/A 1.50 Clayey Silt 8.51 4 23 11.5 PI LS Heave Potential Low/ Medium 487/2/FI/B 2.10 Silty Clay 11.4 8 15 7.5 Low TH5 487/5/FI 1.50 Silty Clay 10.71 6 17 8.5 TH7 487/7/FI/A 0.80 Silty Clay 11.4 4 20 10 Low/ Medium Low/ Medium 487/7/FI/B 1.90 Silty Clay 2.1 4 5 2.5 Low TH11 487/11/FI 1.60 Silty Clay 9.15 7 15 7.5 Low TH13 487/13/FI 1.60 Silty Clay 8.68 7 14 7.0 Low TH16 487/16/FI 1.50 Silty Clay 11.05 8 13 6.5 Low TH18 487/18/FI 2.5 Silty Clay 9.96 9 12 6.0 Low Page 20
Where: Equiv. PI = Equivalent Plasticity Index of whole sample % Clay = Percentage clay PI = Plasticity Index LS = Linear Shrinkage Results reveal relatively low clay percentages yet inflated Linear Shrinkage and Plasticity Indices, as high as 11.5 and 23, respectively (hence the three low/ medium heave potential as indicated in Table 6.2). Results of clay activity have been assessed and are presented in Figure 6.2. These indicate low potential for heave: mainly as a result of the low clay content. The high Linear Shrinkage and relatively high PI suggest nonetheless that the unconsolidated materials may heave and shrink on wetting and drying respectively and therefore either avoided beneath foundations or accounted for in foundation design. Figure 6.2 Clay activity chart Page 21
7. GEOTECHNICAL APPRAISAL 7.1 INTRODUCTION This section of the report provides geotechnical findings as based on the field tests and laboratory test results. 7.2 ENGINEERING GEOLOGY Trial holes sited and excavated at positions requested by MBB Consulting Engineers indicate a site underlain by loose to medium dense colluvial silt (or fill), overlying pedogenic gravelly clayey silt ferricrete which includes occasional rounded pebbles and cobbles in some of the deeper trail holes; in turn overlying residual clay, with refusal in some trial holes on mudstone or siltstone. The nineteen trial holes generally intersect a relatively consistent profile type but with varying depth to rock/ TLB refusal as determined by individual locations. The trial holes that intersect rock are numbered 1, 3, 4, 10 and 15. These are located on slightly higher lying areas on the eastern and central parts of the site (see Figure 5.1) and suggesting thereby, especially after consideration of the expected high clay content in the unconsolidated materials, founding on rock in these zones to nullify geotechnical problems with heave and shrinkage of clay on wetting and drying. This will though require additional detailed investigation in this area, using rather an excavator to provide greater depth of penetration, to confirm any near surface rockhead. Alternatively consideration will need to be given to founding in the deeper colluvial, pedogenic, and residual soil areas with the understanding that this will require foundation methods capable of accommodating post-construction differential movements. The magnitude of the differential movements will only become known once laboratory results have been received. 7.3 STRUCTURE FOUNDATIONS The best possible geotechnical outcome would be to construct foundations for the new buildings on rock since this will provide high bearing capacity and obviate geotechnical problems derived from active clays. Possibly too, albeit of a lesser nature, differential settlement in the near-surface loose colluvium and uncompacted fill. For foundations on rock normal strip footings would be used and if the rock does prove somewhat deep: perhaps in excess of 1,5m, then a system such as trench-fill could be considered. In trench-fill excavations are taken down to rock but then backfilled using compacted inert geotechnical materials, such as weathered dolerite sabunga, or soilcrete, or low strength mass concrete, etc., to normal strip footing invert level, and then continue using standard strip footings. Also to consider could be spot bases with ground beams and suspended floors/ strengthened floor slab if the rockhead contact is not too deep say within 5m of surface. Foundations in deeper unconsolidated materials will require more intricate structural foundation solutions to accommodate the differential foundation movements that may occur, albeit the low/ medium heave potential predicted. These could include:
Relatively wider and deeper footings with steel reinforcement; brickforce in the walls; and articulation of the structure by creating preformed structural cracks as per structural design requirements Alternatively stiffened raft foundations or even piling. The latter though will require additional investigation in the form of rotary cored borehole drilling. The following precautionary procedures though should, as a general rule and irrespective of the magnitude of perceived differential movements, also be considered when founding in these materials. Ensure all surface run-off is led away from structures with no ponding up against any buildings Discourage growing of plants alongside building walls and ensure no trees are planted within 10m of structures Construct a 1,5m concrete platform around each structure to move the zone of evapotranspiration away from foundation areas, and in so doing minimise moisture fluctuations. A deep subsoil drain with plastic liner on the building side of the trench can also assist in minimising moisture changes beneath foundations Provide flexible couplings for all buried services in order to minimise chances of rupture. These various options will need to be considered by the structural engineer who will ultimately decide and be responsible for the foundation designs 7.4 GEOTECHNICAL RECOMMENDATIONS It is recommended that foundations for the new structures be taken down to rock, if possible, since this is the preferred geotechnical solution. If founding on rock is not possible, then it is recommended that foundations be constructed on reinforced strip footings a minimum of 1,5m below ground (to minimise moisture fluctuations), brickforce provided in the brickwork, articulation provided in the structure to accommodates any latent differential movements and other general recommendations including a concrete paving surround, landscaping etc. as indicated in the previous section.
Appendix 1 - Trial Hole Logs
Appendix 2 DCP Test Results
Appendix 3 Laboratory Test Results