Housing Geotechnical Report

Technical Report: 2007 / 12 / 03 / DGSI
Document version 1.0
Detailed Engineering Geological Investigation in

support of the proposed THORNHILL
MINISTERIAL HOUSING PROJECT, PORT ALFRED
Prepared for:
Bigen Africa Services (PTY) Ltd on behalf of

ABSA DevCo (PTY) Ltd
December 2007
Compiled by
FN De Jager, S Potgieter, F Calitz
Thornhill Ministerial Housing Project – Port Alfred - Detailed Engineering Geological Investigation
Technical report: 2007 / 12 / 03 / DGSI
Detailed Engineering Geological Investigation in

support of the proposed THORNHILL
MINISTERIAL HOUSING PROJECT, PORT ALFRED
November 2007
Conducted on behalf of:

Bigen Africa Services (PTY) Ltd
P.O. Bo x 2697
BEACON BAY
5205
Mr. Le Roux Niemann

Tel. No.: (043) 726 0860
Fax. No.: (043) 726 1036
Compiled by:
Project team:
FN De Jager (BSc Hons, Engineering Geology) Pr. Sci. Nat
S Potgieter (BSc Hons, Engineering Geology) Pr. Sci.Nat
F Calitz (MSc, Soil Science) Pr. Sci. Nat
Z Ngwaja (Grade 10)
J Potgieter (BTec, Civil Engineering)
EASTERN CAPE PROVINCE: 8 & 10 Sansom Road, Vinc ent, East London,
Postnet 203, Pri vate Bag X9063, East London, 5200
Tel: +27-43-726 2070 Fax: +27-43-726 9232,
www.ages-group.c om
Di rec tors : SJ Pretorius (MD ) T N goe pe J A Myburgh JJ P V ivi er R Crosby

JC V ivi er (P hD ) A Wi ere nga J B otha F C al itz K Ayi si (PhD)
FN de J ager S Potgi eter H J annasc h E van Zyl J C la rk
C va n der Li nde M H Grobl er J R Bula si gobo
REPORT DISTRIBUTION LIST
Name Institution
Le Roux Niemann Bigen Africa Services (PTY) Ltd
DOCUMENT HISTORY
Report no Date Version Status

2007 / 12 / 03 / DGSI 14 Dec 2007 1.0 Final Draft
AGES i
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Environmental Services South Africa (P ty) Ltd, which has been obtained beforehand. This document is
prepared exclusively for Bigen Africa Services (PTY) Ltd on behalf of ABSA DevCo (PTY) Ltd and is
subject to all confidentiality, copyright and trade secrets, rules, intellectual property law and practices of
South Africa.
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Table of contents
1 INTRODUCTION ............................................................................................................. 1
1.1 GENERAL....................................................................................................................... 1
1.2 T ERMS OF REFERENCE.................................................................................................... 1
1.3 SCOPE OF THE INVESTIGATION....................................................................................... 1
1.4 RESULTS OF PREVIOUS INVESTIGATIONS ........................................................................ 1
2 INFORMATION SOURCES ........................................................................................... 3
3 S ITE DES CRIPTION ....................................................................................................... 4
3.1 LOCATION OF THE STUDY AREA..................................................................................... 4
3.2 T OPOGRAPHY................................................................................................................. 5
3.3 DRAINAGE ..................................................................................................................... 5
3.4 CLIMATE........................................................................................................................ 6
3.5 VEGETATION.................................................................................................................. 6
3.6 REGIONAL SEISMIC INTENSITY....................................................................................... 7
4 NATURE OF THE IN VES TIGATION .......................................................................... 8
4.1 DESK STUDY.................................................................................................................. 8
4.2 FIELD WORK .................................................................................................................. 8
4.3 LABORATORY TESTING .................................................................................................. 8
4.4 REPORTING.................................................................................................................... 9
5 REGIONAL GEOLOGIC AL S ETTING...................................................................... 10
5.1 REGIONAL STRATIGRAPHY .......................................................................................... 10
5.2 PROMINENT GEOLOGICAL STRUCTURES ...................................................................... 10
5.3 T RENCHING.................................................................................................................. 10
5.3.1 Excavation of trial pits ......................................................................................... 10
5.3.2 Generalised engineering geological parameters ................................................. 11
5.3.3 Generalised soil profile........................................................................................ 12
5.4 GROUNDWATER OCCURRENCES .................................................................................. 13
6 GEOTECHNICAL EVALUATION.............................................................................. 14
6.1 ENGINEERING AND M ATERIAL CHARACTERISTICS....................................................... 14
6.1.1 Sampling............................................................................................................... 14
6.1.2 Soil test results: aeolian ....................................................................................... 14
6.1.3 Soil test results: colluvium / reworked aeolian (slightly ferruginised) ................ 15
6.1.4 Soil test results: pebble marker horizon .............................................................. 16
6.1.5 Soil test results: residual quartzite....................................................................... 17
6.2 DYNAMIC CONE PENETROMETER TESTING .................................................................. 18
6.3 SLOPE STABILITY AND EROSION.................................................................................. 19
6.4 EXCAVATION CLASSIFICATION – BULK SERVICES ....................................................... 19
6.5 IMPACT OF GEOTECHNICAL CHARACTER ON SUBSIDY HOUSING DEVELOPMENT ........ 20
7 S ITE CLASS IFICATION .............................................................................................. 22
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7.1 GENERAL..................................................................................................................... 22
7.2 M OST FAVOURABLE FOR RESIDENTIAL DEVELOPMENT ................................................ 22
7.2.1 Zone A1 ................................................................................................................ 22
7.2.2 Zone A2 ................................................................................................................ 22
7.3 LEAST FAVOURABLE FOR RESIDENTIAL DEVELOPMENT ............................................... 23
7.3.1 Zone B .................................................................................................................. 23
8 FOUNDATION RECOMMENDATIONS & SOLUTIONS ....................................... 24
8.1 Z ONE A1...................................................................................................................... 24
8.2 Z ONE A2...................................................................................................................... 25
9 DRAINAGE ..................................................................................................................... 26
9.1 ALL ZONES................................................................................................................... 26
10 S PECIAL PRECAUTIONARY MEAS URES........................................................... 27
10.1 ON-SITE SANITATION SYSTEMS................................................................................. 27
10.2 CONSTRUCTION MATERIAL SOURCES........................................................................ 27
10.2.1 Building material .............................................................................................. 27
10.2.2 Road construction ............................................................................................. 27
11 CONCLUS IONS & RECOMMENDATIONS .......................................................... 29
12 BIBLIOGRAPHY ........................................................................................................ 32
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Appendixes
APPENDIX A – Detailed trial pit profile logs
APPENDIX B – Detailed Dynamic Cone Penetrometer data (DCP data)
APPENDIX C – Laboratory analysis results
List of Maps
MAP 1: Regional Geology and Locality Map
MAP 2: Detailed Site Layout Map
MAP 3: Development Potential Zonation Map
List of Tables
Table 1: Summarised soil test results – Aeolian 15
Table 2: Summarised soil test results – reworked aeolian / colluvium (slightly ferruginised) 16
Table 3: Summarised soil test results – Pebble marker horizon 17
Table 4: Summarised soil test results – Residual quartzite 18
Table 5: Summarised processed soil test results 84
List of Figures
Figure 1: Regional site locality (Google Earth) 4
List of Photos
Photo 1: General topography – very gentle to gentle slopes 5
Photo 2: General study area vegetation 7
Photo 3: Excavation of trial pit in progress 11
Photo 4: General soil conditions encountered on site – aeolian (left) & residual quartzite (right) 13
Photo 5: Dynamic Cone Penetrometer (DCP) test in progress 19
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1 INTRODUCTION
1.1 General
A detailed engineering geological investigation was conducted on a single farm portion known as the
Remainder Portion 4 of The Farm “Thornhill” Location No. 388. with the aim of determining and
evaluating the engineering geological characteristics of the in-situ soil material underlying the project
area with regard to the proposed residential development. This investigation was done on
approximately 50% of the total study area as a first phase on request of Bigen Africa Services (Pty) Ltd.
1.2 Terms of reference

The investigation was requested by Messrs. Bigen Africa Services (Pty) Ltd and Absa Property
Development (Absa DevCo (Pty) Ltd), as confirmed in the Letter of Appointment dated 11 September
2007 (Ref No 1012/00). The study was conducted based on the guidelines set by the National
Department of Housing (GFSH-2, 2002) with regard to geotechnical investigations for residential
development.
1.3 Scope of the investigation

The investigation had the following aims:
• to determine and evaluate the mechanical properties of the soil material occurring within the
boundaries of the study area with regard to the construction of residential buildings
• to determine the suitability of the natural soil materials for use as compacted fill
• to evaluate site excavatability
• to recommend measures to be implemented during design and development of the area
1.4 Results of previous investigations

The results of a detailed geotechnical site investigation conducted directly to the west to southwest of
the present study area reveal the following (Bopite Engineering Geologists cc, Report no. BEG/97024,
1997):
• Fifty trial pits were excavated and 30 disturbed soil samples were taken for analysis
• The investigation revealed fairly homogenous sub-soil conditions and the following soil or rock
horizons were identified;
o Fill with rubbish, ash and rubble
o Silty sand topsoil of Aeolian origin
o Sandy clay colluvium
o Gleyed sandy clay, also of colluvial origin
o Calcrete
o Weathered shale and quartzite
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• The investigation facilitated subdivision of the study area into three development potential
zones (no zonation map available):
o Zone A – Areas underlain by clayey material over weathered bedrock (developable
with moderate precaution)
o Zone B – Areas underlain by gleyed sandy clay colluvium (developable with
precaution)
o Zone C – Areas underlain by sandy clay colluvium (developable with extreme
precaution)
• The above-mentioned zonal sub-divisions show that a number of engineering geological
constraints exist in the study area which could have a restricting affect on the proposed
housing development
• Major constraints include medium expansive clay and collapsible soil throughout the study
area. Other hazards include low bearing capacities at the normal founding depth, dispersive
and compressible soil, differential settlement, perched water tables and patches of shallow
bedrock
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2 INFORMATION SOURCES
The following sources of information were used during the investigation:
Geological maps
- Geological map of the Republic of South Africa and the Kingdoms of Lesotho and
Swaziland, 1997; scale 1 : 1 000 000.
- 3326 GRAHAMSTOWN, scale 1 : 250 000.
Hydrogeological maps
- 3126 QUEENSTOWN, scale 1 : 500 000.
Topographical map
- 3326 DB PORT ALFRED, Third Edition, 1998; scale 1: 50 000.
Electronic maps
- Site layout maps supplied by Bigen Africa Services (Pty) Ltd in hardcopy and electronic
format
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3 SITE DESCRIPTION
3.1 Location of the study area

The project area is located on the remainder Portion 4 of The Farm “Thornhill” Location No. 388.
approximately 3.5 km to the north northeast of Port Alfred in the Ndlambe Local Municipality of the
Cacadu District Municipality, Eastern Cape Province. The project area is situated adjacent to the
eastern side of the main tar road that connects Port Alfred with Bathurst in the direct vicinity of Nemato
township. The regional locality of the project area is indicated in the Figure 1 below, as exported from
Google Earth.
The central point of the project is roughly defined by the following coordinate (geographic, WGS84):
Latitude: 33.561786 ° S
Longitude: 26.902380 ° E
Figure 1: Regional site locality (Google Earth)
AGES 4
3.2 Topography
The general topography of the area can be characterized as slightly undulating hills with flat to
moderate slopes and small drainages. The highest topographical point is situated to the northeast of
the project area at an elevation of 110 mamsl. The study area is located at an elevation of between 70
and 95 m above mean sea level.
The proposed development is situated on the central upper and southeastern portion of the weakly
defined ridge crest. The steepest slopes occur in the upper western portion of the area associated with
the tributaries of the Kowie River. A study of the topographical map indicated slopes of between 1.5 and
3 degrees over the majority of the study area with up to 7 degrees calculated in the upper western
portion.
The study area does not exhibit any significant topographical features.
Photo 1: General topography – very gentle to gentle slopes
3.3 Drainage
The project area is drained by means of surface flow and sheet wash to the southeast and southwest
into the tributaries of the Rufane- and Kowie Rivers respectively. The area is situated approximately 4
km from the Indian Ocean.
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No prominent drainage features occur in the direct vicinity of the proposed site. The position of the
1:100 year flood line was not available as part of this investigation. No development should take place
below this flood line. It is however expected that this will not influence the proposed development.
3.4 Climate
The study area is located in the Summer Rainfall Zone of the Republic of South Africa in quaternary
catchment P40C within the Bushmans Catchment Management area. The eastern boundary of the
project area is located on the watershed and subsequent boundary of quaternary catchments P40C and
P40D. The area is expected to receive a mean annual precipitation of between 612 and 665 mm, and
has an annual evaporation of between 1300 and 1500 mm (Midgley et al, 1994).
The climatic N-value (Weinert, 1980) of the area is less than 5, indicating that chemical decomposition
of the constituent minerals of the underlying bedrock, rather than mechanical disintegration, is the
dominant mode of weathering.
3.5 Vegetation
The natural vegetation occurring in the study area can be classified as Alexandria Forest according to
Acocks. The natural vegetation has not been disturbed extensively due to urban development. The
general vegetation is indicated in Photo 2 below.
AGES 6
Photo 2: General study area vegetation
3.6 Regional seismic intensity

According to Fernandez et al (1979) the regional seismic hazard in the project area can be defined as
follows:
The area exhibits a 90 % probability of the occurrence of a seismic event not exceeding Class
V to VI-intensity [Strong] (i.e.: equivalent to a seismic event registering 4. 9 to 5.4 on the Richter
Scale) within a period of 100 years.
The area exhibits a 90 % probability of the occurrence of a seismic event not exceeding VI to
VII-intensity1 [Very Strong] (i.e.: equivalent to a seismic event registering approximately 5.5 to
6.1 on the Richter Scale) within a period of 500 years.
In this light, the seismic risk of the study area can be classified as SLIGHT, and as such requires that
Masonry Class B design and construction measures be implemented, incorporating good workmanship
and reinforced mortar work, but specific design and construction measures to resist the effect of lateral
forces on the proposed development is not deemed necessary.
1 The effects of a Class VII-intensity event (categorized as strong to very strong) can be summarized as follows:
- Difficult to stand
- Noticed by drivers of motorcars
- Hanging objects quiver
- Furniture broken
- Damage to weak materials (such as adobe: poor mortar; low standards of workmanship; weak horizontally ) including
cracks
- Weak chimney s broken at roof line
- Fall of plaster, loose bricks, stones, tiles, cornices, unbraced parapets and architectural ornaments
- Some cracks in ordinary workmanship and mortar
- Small slides and caving-in along sand or gravel banks and concrete irrigation ditches will be damaged
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4 NATURE OF THE INVESTIGATION
4.1 Desk study

The investigation commenced with the conducting of the following actions:
• the collation and evaluation of available geological and geotechnical information
• the compilation of base map showing identified land forms, regional geological setting and soils
classification
• the conducting of a preliminary slope analysis to delineate areas with either steep- or very
gentle slopes
During this phase, the results of engineering geological investigations conducted in the vicinity of the
study area were evaluated and collated, in order to determine the level of work to be conducted during
this study.
4.2 Field work

Trial pits were placed on an open grid spacing throughout the study area in such a way as to accurately
describe the general soil conditions occurring within the boundaries of the study area. The succession
of soil and rock layers exposed within these pits were logged according to the industry-standard method
proposed by Jennings et al (1973), and samples were taken of the soil material deemed to be important
to the proposed development.
It must be noted that the investigation was conducted based on a land facet approach, where the study
area was divided into land forms by grouping together areas exhibiting similar geology, topography and
drainage.
Dynamic Cone Penetrometer (DCP) tests were conducted at surface level at each trial pit.
4.3 Laboratory testing

The following tests were conducted on soil samples taken during the field work phase by a properly
accredited soils laboratory (Messrs. Controlab, East London):
Standard foundation indicator tests were conducted on disturbed soil samples in order to determine its
composition, to evaluate the heave and compressibility potential of these soils, and to calculate the
maximum heave and/or differential settlement that can be expected. The following tests were
conducted:
• Atterberg Limits (Liquid Limit and Plasticity Index) and Linear Shrinkage
• Particle-size distribution (utilizing both sieve- and hydrometer methods)
• Soil moisture chemistry (pH, Electrical Conductivity & % water saturation)
AGES 8
Standard road indicator tests were conducted on a bulk soil samples in order to determine its
composition (i.e.: the relative percentages of gravel, sand, silt and clay present within each sample),
and to evaluate the suitability of these materials for use in the construction of roads within the township,
as well as the construction of compacted and layered fills. The following additional tests were
conducted:
• Maximum Dry Density versus Optimum Moisture Content
• Californian Bearing Ratio versus Compaction Effort (MOD AASHTO method)
• Soil moisture chemistry (pH, Electrical Conductivity & % water saturation)
The undisturbed soil samples were tested for its Unconfined Compressive Strength test (UCS) in kPa in
order to determine and verify the accuracy and validity of DCP testing and to obtain a generalised
indication of the bearing capacity of the soils.
4.4 Reporting
The investigation concluded with the compilation of a technical report detailing all methodology utilised
during the study and all results obtained. This report includes a detailed potential evaluation of the site
in terms of residential development, based on the results of the geotechnical investigation, with
recommendations regarding foundation design and construction, excavatability, and the presence of
construction material sources on site
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5 REGIONAL GEOLOGICAL SETTING
5.1 Regional Stratigraphy

According to the available geological information, the study area is underlain by shale and quartzite of
the Weltevrede Formation2 of the Witteberg Group that is part of the Cape Supergroup sequence of
rocks. The geology dip to the northeast at an angle of between 25 and 35 degrees.
No dolerite dyke or sill intrusions occur within the surroundings of the study area.
The area does not reflect any risk for the formation of sinkholes or subsidence’s caused by the
presence of water-soluble rocks (for example: dolomite or limestone). Rocks from the surrounding
geological formations of the Algoa Group are comprised mostly of calcareous sandstones and
limestones and are deemed to be soluble. Small outliers of the Alexandria- and Nanaga Formation
occurs directly to the south of the study area. If any of these formations are exposed during
development further investigation will be required.
The regional geology of the study area and its surroundings are indicated in Map 1.
5.2 Prominent Geological Structures

The available geological information does not indicate the presence of any prominent geological
structures within the vicinity of the study area.
5.3 Trenching
5.3.1 Excavation of trial pits

A total of 40 trial pits, numbered BT1/ TP/01 to BT1/ TP/40 (Map 3), was excavated by means of a Volvo
RL 70 TLB-type light mechanical excavator on 29 and 30 October 2007, at which time the exposed soil
layers were profiled and soil material sampled.
Detailed trial pit profile logs are included as Appendix A.
2 The lithology of the Weltevred e Formation clos ely res embles that o f the Sandpoo rt Formation o f the
Bokkeveld Group, the main di fference being th at sandstone is more abund ant, paler in colour and virtually
feldspar free. Plant stems, particularly protolcopods and psilophytes, occur sporadically. Some small, poorly
preserv ed marin e inverteb rate fossils were found just below the top o f the Weltevrede in Howieson’s Poort,
southwest of Grahamstown. The sediments were probably deposited under the same conditions of the Sandpoort
Formation of the Bokkev eld Group. (The shale appears to represent upper prodelta slope, outer delta-front
platform, interdistributary bay and tidal-flat sediments, while the sandstone represent coalescent distributary
mouth-bar deposits and coalescent delta-ront sheet sands).
AGES 10
Photo 3: Excavation of trial pit in progress
5.3.2 Generalised engineering geological parameters

The following general engineering geological characteristics were noted:
• Excavatability
It was possible to excavate the trial pits to a depth of between 2.00 and 3.60 m (mean 2.70 m)
by means of a TLB-type excavator without difficulty.
• Rock and pedocrete outcrops

No rock and pedocrete outcrop was noted in the study area.
• Sidewall stability
Localised collapse and overbreak of trial pit side walls occurred during profiling and sampling.
• Groundwater seepage
Groundwater seepage was not encountered in the trial pits. Moist soil conditions were
encountered over the majority of the area.
AGES 11
5.3.3 Generalised soil profile

Note: this description is based on field observations, and does not reflect the results of any laboratory
tests.
The results of the trenching phase indicate that the study area is covered by a layer of aeolian material.
This material consists of several horizons exhibiting slightly different characteristics. The top horison
consists of silty sand exhibiting a loose to very loose consistency and little or no structure with a
thickness of between 0. 30 and 1. 00 m (mean 0.60 m). This horizon is underlain by clayey sand
exhibiting a soft consistency and micro shattered structure with a thickness of between 0.20 and 1.30 m
(mean 0.50 m). The bottom aeolian horizon consists of clayey sand with a firm to stiff consistency and
shattered structure and a thickness of between 0.20 and 2.80 m (mean 1. 4 m). In localised areas this
horizon consists of sandy clay with scattered ferricrete nodules with a diameter of up to 5 mm exhibiting
a firm consistency and shattered and weakly slickensided structure.
The aeolian material is mainly underlain by a Pebble Marker Horizon composed of clayey sand with
frequent to abundant quartz gravel with a diameter of up to 60 mm. This layer exhibits a firm
consistency, and is between 0.10 and 0.70 m thick (mean 0.25 m). This horizon indicates the bottom of
the transported soil material.
The transported cover is underlain from a depth of between 0.90 and 2.60 m (mean 1.80 m) by residual
sandstone / quartzite composed of clayey sand with a firm consistency and little or no structure.
Highly weathered quartzite bedrock was encountered in only two trial pits from a depth of between 1.30
and 2.0 m, exhibiting a very soft to moderately hard rock consistency. Joint surfaces are narrow,
stained and medium rough.
The general soil conditions as observed on site is indicated in Photo 4 below.
AGES 12
Photo 4: General soil conditions encountered on site – aeolian (left) & residual quartzite
(right)
5.4 Groundwater Occurrences

Groundwater seepage was not encountered in the trial pits. However, the localised presence of
ferruginized material at relatively shallow depth indicates the seasonal formation of perched water
tables directly after heavy precipitation events.
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6 GEOTECHNICAL EVALUATION
6.1 Engineering and Material Characteristics
6.1.1 Sampling
The following samples were taken during the site investigation and trial pit profiling:
• Aeolian : 16 disturbed samples
: 6 bulk samples
: X undisturbed samples
• Reworked Aeolian / Colluvium (slightly ferruginised) : 1 disturbed sample
• Pebble Marker Horizon : 1 disturbed sample
• Residual quartzite : 2 disturbed samples
Laboratory soil test data are included as Appendix B.
6.1.2 Soil test results: aeolian

The results of foundation indicator tests conducted on disturbed samples of the aeolian soil material are
summarized in Table 1 below. It is evident that this material exhibits a highly variable composition and a
diverse range of geotechnical characteristics.
In the light of the soil test results and visual observation, the aeolian material is deemed to be
potentially slightly to very highly compressible / collapsible, and potentially slightly to moderately
expansive. This material exhibits a calculated settlement due to collapse / compression of up to and
greatly in excess of 10 mm (up to 90 mm) and a calculated heave of between and potentially in excess
of 15 and 30 mm (20 mm calculated). The aeolian material was not tested for but is deemed potentially
highly dispersive based on available information from previous investigations.
It must be noted that the aeolian material is deemed neutral to slightly alkaline and highly to very highly
saline.
The results of road indicator tests conducted on 6 bulk samples of this material are summarized in
Table 1. The material is deemed moderately suitable for use in the construction of layered fills,
classifying as a G7 to weaker than G10 (<G10) type material. The results of these tests indicate that
this material’s reaction to compaction is highly variable, with CBR-values in excess of between 1 and 27
(mean 12) recorded at compaction efforts of 95% MOD AASHTO and between 2 and 59 (mean 24 ) at
compaction efforts of 100% MOD AASHTO.
The Unconfined Compressive Strength (UCS) of the material varies between 110 and 470 kPa from a
depth of between 0.75 to 2.00 mbgl.
AGES 14
Table 1: Summarised soil test results – Aeolian
6.1.3 Soil test results: colluvium / rew orked aeolian (slightly ferruginised)
The results of foundation indicator tests conducted on the disturbed sample of the slightly ferruginised
colluvium / reworked aeolian material are summarized in Table 2 below. It is expected that this material
will exhibit a diverse range of geotechnical characteristics depending on the degree of ferruginisation
and general composition.
In the light of the soil test results and visual observation, the material is deemed to be potentially
moderately collapsible / compressible. The material is not deemed to be potentially expansive. The
material was not tested for but is deemed potentially highly dispersive based on available information
from previous investigations.
It must be noted that the material is deemed neutral to slightly alkaline and very highly saline.
AGES 15
Table 2: Summarised soil test results – rew orked aeolian / colluv ium (slightly ferruginised)
6.1.4 Soil test results: pebble marker horizon

The results of foundation indicator tests conducted on the disturbed sample of the pebble marker
horizon are summarized in Table 3 below. It is expected that due to the composition of this material will
exhibit a diverse range of geotechnical characteristics.
In the light of the soil test results and visual observation, the pebble marker horizon material is deemed
to be potentially slightly compressible. The material is not deemed to be potentially collapsible or
expansive. The material was not tested for but is deemed potentially highly dispersive based on
available information from previous investigations.
It must be noted that the pebble marker horizon material is deemed neutral to slightly acidic and very
highly saline.
AGES 16
Table 3: Summarised soil test results – Pebble marker horizon
6.1.5 Soil test results: residual quartzite

The results of foundation indicator tests conducted on the disturbed sample of the residual quartzite are
summarized in Table 4 below. The composition of this material does not vary significantly and therefore
the material is not expected to exhibit a diverse range of geotechnical characteristics.
In the light of the soil test results and visual observation, the residual quartzite material is deemed to be
potentially moderately to very highly collapsible / compressible. The material is not deemed to be
potentially expansive. The material was not tested for but is deemed potentially highly dispersive based
on available information from previous investigations.
It must be noted that the residual quartzite material is deemed neutral to slightly alkaline and very highly
saline.
AGES 17
Table 4: Summarised soil test results – Residual quartzite
6.2 Dynamic Cone Penetrometer testing

A total of 40 Dynamic Cone Penetrometer (DCP) tests were conducted within a distance of 1 m from
trial pit sidewalls up to a depth of approximately 1 mbgl (Map 2). Results are summarised below with
detailed DCP data and graphs attached in Appendix B for reference.
• Aeolian material was intersected at all 40 DCP tests. Data obtained from the DCP testing on
the aeolian soil material occurring from ground level to 1 mbgl revealed calculated minimum
and maximum UCS values of between 19 and 816 kPa (mean 40 to 241 kPa).
• Pebble marker horizon material was intersected at 3 of the 40 DCP tests. Data obtained from
DCP testing on the pebble marker horizon soil material occurring from a depth of approximately
0.9 mbgl revealed calculated minimum and maximum UCS values of between 141 and 1362
kPa (mean 262 to 645 kPa).
• Colluvium / Reworked Aeolian material was intersected at 3 of the 40 DCP tests. Data obtained
from DCP testing on the soil material occurring from a depth of between 0.5 to 0.9 mbgl
revealed calculated minimum and maximum UCS values of between 52 and 193 kPa (mean
AGES 18
111 to 144 kPa).
• Residual quartzite was intersected at only 1 of the 40 DCP tests from a depth of approximately
0.9 mbgl. Data obtained from DCP testing revealed a calculated UCS of approximately 84 kPa.
Photo 5: Dynamic Cone Penetrometer (DCP) test in progress
6.3 Slope Stability and Erosion

In the light of the very gentle to moderate slopes present across the site, specialised methods for the
stabilisation of cuts into the natural slopes are not deemed necessary.
The potential dispersivity of the transported and residual materials are indicative thereof that the soil
material covering and underlying the whole study area may be prone to surface- and sub-surface (i.e.:
pipe-) erosion.
6.4 Excavation Classification – Bulk Services

No significant problems are foreseen within the aeolian, pebble marker horizon and residual quartzite
material occurring from a depth of between surface and 3.5 m over the majority of the project area
AGES 19
during the excavation of bulk service or foundation trenches by means of pick-and-shovel or a light
mechanical excavator (soft excavation class).
The weathered quartzite bedrock with a very soft- to soft rock consistency occurring from a depth of
between 0.1.3 and 2. 0 m may hamper the excavation of service trenches by hand, requiring the use of
a light mechanical excavator, power tools, or possibly a heavy mechanical excavator to remove
material (soft to intermediate excavation class).
The following additional comments on excavation of service trenches apply:
• Trenches may have to be dewatered, due to the seasonal formation of perched water tables in
localised areas of the site at relatively shallow depth, especially after heavy precipitation
events.
• The side walls of excavations in excess of 1.0 m should be shored to prevent injury or death
due to the high risk and probability of side wall failure by collapse and/or overbreak.
6.5 Impact of Geotechnical Character on Subsidy Housing Development

The geotechnical characteristics exhibited by the soil material covering the study area will have the
following effects with regard to implementation of subsidy housing developments:
1. Seepage / groundwater
The area exhibits the potential for the seasonal occurrence of perched water tables at a depth
of less than 1.0 m beneath ground surface in localised areas (Category 1).
= Subsurface drainage / improved damp-proofing measures to be implemented

beneath structures
= Service trenches to be dewatered during construction
2. Erodability of soil
The majority of the uppermost soil horizon (0 to 750 mm) over the project area classify as SM
and CL according to the Unified Soil Classification. The average slope measured in any
direction is however less than 1: 7,5 (± 7.5°).
= No significant effect
3. Difficulty of servicing of land due to slopes

The average calculated slopes across the majority of the project area (utilising the 1: 50 000
topographical map) are Type 2 (1:20 to 1: 10) with large portions less than 1:20 but steeper
than 1:100. The steepest occur associated with the drainages of the Kowie River, nl Type 3
(1:7,5 to 1: 10).
AGES 20
= Difficulties associated with the provision of waterborne sanitation and the

drainage of sites / provision of pump stations may be encountered
= Terracing for houses / additional masonry units in foundation walls required
= Terracing for houses required. Additional earthworks to roads and storm water
control measures.
4. Difficulty of excavation
The average slopes within the study area is less than 1:10, between 80 and 100% of the
material occurring to a depth of 1.5 m beneath the pre-development level classifies as soft rock
excavation.
= No applicable
5. Precautionary measures in sites underlain by dolomite/limestone

The geological map does not indicate the presence of soluble rock material (ie limestone /
dolomite) within the project area but well on the outskirts of the site. This material was not
encountered in any of the trial pits. Should this material be encountered during the excavation
of bulk service or foundation trenches, further investigation will be required and necessary
precautionary measures implemented.
= Not applicable (pending verification in Phase 2 investigation)
6. Founding conditions
The soil material covering and underlying the area is deemed potentially moderately expansive
(Class H2) and very highly compressible and/or collapsible (Class H3) as indicated in Map 3.
= Masonry houses will require foundation design, building procedures and

precautionary measures to be in accordance with Tables 5, 6 and 7 of Part 1
Section 2 of the NHBRC Home Building Manual
AGES 21
7 SITE CLASSIFICATION
7.1 General
The study area can be divided into three development potential zones (Map 3), based on the regional
physiographic- and geological setting, and the geotechnical characteristics of the soil material exposed
in each test pit. Although the study area exhibits some geotechnical characteristics deemed to have an
adverse effect on residential development, these characteristics do not disqualify the area from being
used for the proposed development, but rather require the implementation of site-specific precautionary
measures with regard to design and construction of the proposed structures.
7.2 Most favourable for residential de velopment
7.2.1 Zone A1
This zone is covered by a thick layer of aeolian topsoil with varying thicknesses that is underlain in
localised areas by a pebble marker horizon, residual quartzite and highly weathered quartzite bedrock
and is deemed suitable for residential development (ZONE A1), provided due cognisance is given to
the following adverse geotechnical characteristics:
• The occurrence of a thick layer of aeolian material of variable thickness of potentially slightly to
very highly compressible & collapsible soil with a maximum differential settlement greatly in
excess of 10 mm, and potentially slightly to moderately expansive soil with an expected heave
of up to 15 mm, requiring the implementation of strengthened foundations and masonry
construction
• The seasonal occurrence of perched water tables at relatively shallow depth, requiring the
implementation of damp coarse and an efficient surface drainage system and/or sub-surface
drains
• The occurrence of potentially erodable topsoil that may lead to severe surface erosion in areas
where the natural drainage paths have been disturbed or where a concentration of surface
water occurs, requiring the implementation of an efficient surface drainage system
Zone A1 classifies as NHBRC Site Class C2-H1 – P(perched water table).
7.2.2 Zone A2
This zone is covered by a thick layer of aeolian topsoil with varying thicknesses that is underlain in
localised areas by a pebble marker horizon and residual quartzite and is deemed suitable for residential
development (ZONE A2), provided due cognisance is given to the following adverse geotechnical
characteristics:
AGES 22
• The occurrence of a thick layer of aeolian material of variable thickness of potentially slightly to
excess of 10 mm, and potentially moderately expansive soil with an expected heave of up to 30
mm, requiring the implementation of strengthened foundations and masonry construction
• The occurrence of potentially erodable topsoil that may lead to severe surface erosion in areas
Zone A2 classifies as NHBRC Site Class C2-H2.
7.3 Least favourable for residential development
7.3.1 Zone B
The upper western portion of the study area located within the drainage of the non-perennial tributary of
the Kowie River is deemed the least suitable for residential development (ZONE B), due to a periodic
saturation of the sub-surface material for prolonged periods of time.
In the light of the above-mentioned geotechnical characteristics, it is recommended that this zone be
used as a “green zone” or “stormwater retention zone”, and that no structures be constructed in Zone B.
AGES 23
8 FOUNDATION RECOMMENDATIONS & SOLUTIONS
8.1 Zone A1
It is recommended that EITHER of the following foundation designs be utilised for structures to be
placed within this zone: (Please note that the competent horizon in this zone is composed of aeolian
material occurring from an average depth of 0. 75 to 1.10 mgbl with a UCS of between 110 and 470
kPa.
• OPTION 1 – Stiffened strip footings / Stiffened or Cellular raft

- articulation joints or solid lightly reinforced masonry,
- bearing pressure not to exceed 50 kPa,
- fabric pressure not to exceed 50 kPa,
- Site drainage and service / plumbing precautions
• OPTION 2 – Deep strip foundations

- normal construction with drainage requirements
- fabric reinforcement in floor slabs
- founding on competent horizon
• OPTION 3 – Compaction of in-situ soils below individual footings

- remove in-situ material below foundations to a depth and width of 1.5 times the
foundation width or to a competent horizon and replace with material compacted to
93% MOD AASHTO density at -1% to +2% of optimum moisture content
- Normal construction with lightly reinforced strip foundation and light reinforcement in
masonry
• OPTION 4 – Piled or pier foundations

- reinforced concrete ground beams or solid slabs on piled or pier foundations
- ground slabs with fabric reinforcement
- good site drainage
• OPTION 5 – Soil raft

- remove in-situ material to 1.0m beyond perimeter of building to a depth of 1. 5 times the
widest foundation or to a competent horizon and replace with material compacted to
- Normal construction with lightly reinforced strip footings and light reinforcement in
masonry
AGES 24
8.2 Zone A2
It is recommended that EITHER of the following foundation designs be utilised for structures to be
placed within this zone: (Please note that the competent horizon in this zone is composed of aeolian
material occurring from an average depth of 0. 75 to 1.10 mgbl with a UCS of between 110 and 470
kPa.
• OPTION 1 – Stiffened strip footings / Stiffened or Cellular raft

- articulation joints or solid lightly reinforced masonry,
- bearing pressure not to exceed 50 kPa,
- fabric pressure not to exceed 50 kPa,
- Site drainage and service / plumbing precautions
• OPTION 2 – Piled or pier foundations

- reinforced concrete ground beams or solid slabs on piled or pier foundations
- ground slabs with fabric reinforcement
- good site drainage
• OPTION 3 – Soil raft

- remove in-situ material to 1.0m beyond perimeter of building to a depth of 1. 5 times the
widest foundation or to a competent horizon and replace with material compacted to
- Normal construction with lightly reinforced strip footings and light reinforcement in
masonry / construction type appropriate to residual movements.
- Site drainage and plumbing / service precautions
AGES 25
9 DRAINAGE
9.1 All zones

It is recommended that an efficient surface drainage system be installed around all structures and along
all roads throughout the project area in order to:
• prevent the ponding of water at the surface next to structures directly after heavy precipitation
events, as this may lead to differential settlement under the footings as the saturated material
undergoes densification
• prevent large-scale changes in soil moisture beneath the structures on a seasonal basis
• prevent the seasonal formation of perched water tables (i.e.: short-term groundwater seepage)
within the soil material at shallow depth
• prevent the possible lateral movement of liquids within the upper soil horizons
• reduce the risk of surface erosion in the light of the presence of erodible soil material
The precautionary measures should ideally include:
• the sealing of open ground surfaces by means of either of the following:

- the cultivation of a natural soil cover (e.g.: grass)
- compaction of the soil surface
- bitumen or concrete paving
• the removal of surface water to a distance of at least 1 m beyond structures by means of

watertight paving
• the removal of surface run-off by means of an efficient surface drainage system
• roads should preferably be constructed parallel to the natural surface elevation contours rather
than perpendicular to it, in order to reduce run-off velocities
AGES 26
10 SPECIAL PRECAUTIONARY MEASURES
10.1 On-site sanitation systems

It is recommended that the proposed township be connected to the municipal sewerage removal
system.
Alternatively use can be made of either individual- or communal package plants that yield purified water
for irrigation purposes.
Please note that the use of on-site sanitation systems that relies on seepage for the disposal of liquid
wastes (i.e.: septic tanks equipped with “French Drain”-type soak-away) should be avoided, due to both
an enhanced risk of groundwater pollution due to the seasonal occurrence of perched water tables at
shallow depth, and the impaired functioning thereof due to the perceived low permeability of the
underlying soil and weathered bedrock material.
10.2 Construction material sources
10.2.1 Building material

Guidelines for the different application of sand along with a brief evaluation of the sampled material is
given in the tables below:
The material is classified as suitable to marginally suitable for use as internal plaster due to the high
percentage of material passing the 0. 15 mm sieve. It is recommended that the fraction passing 0. 075
mm be removed by screening prior to use. This fraction will be approximately 14 % of the excavated
material.
The material is classified as marginally to poorly suitable for use as external plaster and high strength
mortar due to the lack of sand material with a nominal size in excess of 0.3 mm and due to the high
percentage of material finer than 0. 15 mm. Even with the material finer as 0.15 mm removed, the
material is still deemed to be marginally suitable, and ideally the material should not be utilised for this
purposed, pending further testing.
The material is classified as suitable to marginally suitable for use as general purpose mortar. I t is
however recommended that the fines fraction be removed prior to utilisation by screening the material
with a 0.075 mm sieve.
10.2.2 Road construction

Based on the results of the laboratory tests, it can be stated that the in-situ soil material covering and
underlying the project area generally rate as excellent to poor for use in the construction of the sub-
AGES 27
base layer of roads. This is due to the depositional character of the soils that resulted in a variable
composition and grading of the materials. The material generally classifies as A-2-4 to A-6 according to
AASHTO.
The aeolian material that covers and underlies the project area generally rate marginally suitable to
unsuitable for use in the construction of the subbase- and selected layers of roads, with TRH14
classifications of G7 to < G10 – type material.
AGES 28
11 CONCLUSIONS & RECOMMENDATIONS

1) A detailed engineering geological investigation was conducted on a single farm portion known as
the Remainder Portion 4 of The Farm “Thornhill” Location No. 388. with the aim of determining and
evaluating the engineering geological characteristics of the in-situ soil material underlying the
project area with regard to the proposed residential development. This investigation was done on
approximately 50% of the total study area as a first phase on request of Bigen Africa Services (Pty)
Ltd.
2) According to the available geological information, the study area is underlain by shale and quartzite
of the Weltevrede Formation of the Witteberg Group that is part of the Cape Supergroup. The site
does not reflect any risk for the formation of sinkholes or subsidences caused by the presence of
water-soluble rocks (dolomite or limestone), and no evidence of mining activity beneath the study
area has been revealed. No geological structures such as fault zones, lineaments or dykes occur in
the project area.
3) The results of this study reveal that the soil material underlying the study area exhibits adverse
geotechnical characteristics that may require the implementation of specific design and/or
precautionary measures to reduce the risk of structural damage, including:
a) The occurrence of a thick layer of aeolian material of variable thickness of potentially slightly to
excess of 10 mm, and potentially moderately expansive soil with an expected heave of up to 30
mm, requiring the implementation of strengthened foundations and masonry construction
b) The seasonal occurrence of perched water tables at relatively shallow depth, requiring the
implementation of damp coarse and an efficient surface drainage system and/or sub-surface
drains
c) The occurrence of potentially erodable topsoil that may lead to severe surface erosion in areas
4) However, these characteristics do not disqualify the whole site from being used for the proposed
development, but rather require the implementation of site-specific precautionary measures with
regard to design and construction of the proposed residential structures.
5) The study area was divided into the following development potential zones, based mainly on the
regional physiographic- and geological setting, and the geotechnical characteristics of the soil
material exposed in each trial pit:
a) Those portions of the project area covered by a thick layer of aeolian topsoil with varying
thicknesses that is underlain in localised areas by a pebble marker horizon, residual quartzite
and highly weathered quartzite bedrock and is deemed suitable for residential development,
AGES 29
but requiring the implementation of precautionary measures to prevent structural damage due
to the occurrence of soils exhibiting adverse geotechnical characteristics. These areas are
defined as Zone A1, and classify as NHBRC Site Class C2 –H1 – P (perched water tables).
b) Those portions of the study area covered by a thick layer of aeolian topsoil with varying
thicknesses that is underlain in localised areas by a pebble marker horizon and residual
quartzite and is deemed suitable for residential development, but requiring the implementation
of precautionary measures to prevent structural damage due to the occurrence of soils
exhibiting adverse geotechnical characteristics. These areas are defined as Zone A2, and
classify as NHBRC Site Class C2 – H2 – P (perched water tables).
c) The upper western portion of the study area located within the drainage of the non-perennial
tributary of the Kowie River is deemed the least suitable for residential development (ZONE B),
due to a periodic saturation of the sub-surface material for prolonged periods of time, is
deemed marginally suitable to unsuitable for residential development. It is recommended that
this zone be used as a “green zone” or “stormwater retention zone”, and that no structures be
constructed within Zone B
6) The effects of adverse geotechnical characteristics exhibited by the soil- and/or rock underlying
Zones A 1, A2 and B with regard to the proposed residential development can is summarised in
Chapters 8, 9 and 10 of this report.
7) The implementation of an efficient surface drainage system is deemed essential around all
structures and along all roads throughout the study area. The implementation of an efficient sub-
surface drainage system is deemed necessary along all roads placed in Zone B.
8) It is assumed that the sanitation needs of the proposed development will be serviced by the existing
municipal sewerage system. Alternatively, use can be made of either individual- or communal
package plants.
9) It is recommended that suitable precautionary measures be taken to protect bulk services and
concrete works against potentially slightly acidic and very highly saline soil material
10) The soil material covering and underlying the project area is classified as marginally suitable for
use as internal and external plaster and as high strength and general purpose mortar, due to the
relatively high percentage of material passing the 0.15 mm sieve. It is recommended that the
fraction passing 0.075 mm be removed by screening prior to use and further testing be conducted.
11) Based on the results of the laboratory tests, it can be stated that the in-situ soil material covering
and underlying the project area generally rate as:
a) excellent to poor for use in the construction of the sub-base layer of roads. This is due to the
AGES 30
depositional character of the soils that resulted in a variable composition and grading of the
materials. The material generally classifies as A-2-4 to A-6 according to AASHTO.
b) marginally suitable to unsuitable for use in the construction of the subbase- and selected layers
of roads, with TRH14 classifications of G7 to < G10 – type material.
12) It is recommended that an engineering geologist or geotechnical engineer inspect all foundation
trenches prior to construction in order to identify and evaluate any soil characteristics in variance
with that found during this investigation.
AGES 31
12 BIBLIOGRAPHY
BYRNE, G, EVERETT, J P and SCHWARTZ, K , 1995.

A guide to practical geotechnical engineering in Southern Africa. Third Edition, Franki.
CALITZ, F, 1998.
The adaptation of ex isting terrain evaluation techniques for application in engineering geological reconnaissance investigations in
developing countries. M.Sc.-thesis, Potchefstroomse Universiteit vir Christelike Hoër Onderwys.
CALITZ, F, 2000.
Technical report on the engineering geological investigation: Proposed Pietersburg Extension 65 middle-income residential development
on a portion of the farm Doornk raal 680-LS. Unpublished Southern Africa GeoConsultants (AGES) report NP/2000/10/02, October 2000.
COMMITTEE OF STATE R OAD AUTHORITIES, 1985.

Technical Recommendations for Highways (TRH) 14: Guidelines for road construction materials.
DEPARTMENT OF WATER AFFAIR S AND FOR ESTR Y, 1997.

A protocol to manage the potential of groundwater contamination from on site sanitation. National Sanitation Co-ordination Office,
Directorate of Geohydrology, Edition 1.
LOW, A B and REB ELO, A G, 1996.

Vegetation of South Africa, Lesotho and Swaziland. The Department of Environmental Affairs and Tourism.
MIDGLEY, D C, PITMAN, W V and MIDDLETON, B J, 1994.

Surface water resources of South Africa 1990, Book of Maps. Water Research Commission report number 298/1.2/9 4.
NATIONAL DATA BANK FOR R OADS, 1974.

List of descriptive land form terms for the naming of land facets. National Institute for Road Research, C.S.I. R., Pretoria.
NATIONAL HOME BUILDERS REGISTRATION COUNCIL, 1999.

Standards and guidelines. Revision 1, February 1999.
SOUTH AFRICAN COMMITTEE FOR STRATIGRAPH Y (SAC S), 1980.

Stratigraphy of South Africa. Part 1 (Comp. L E Kent). Lithostratigraphy of the Republic of South Africa, South West Africa/Namibia, and
the Republics of Bophuthatswana, Transkei and Venda. Handbook of the Geological Survey of South Africa, No. 8, Government Printer,
Pretoria.
THORNBURY, W D, 1969.
Principles of geomorphology, second edition. John Wiley and Sons.
VISSER, D J L, 1989.
“Toeligting tot die 1 : 1 000 000 Geologiese Kaart _ vierde uitgawe, 1984: Die geologie van die Republieke van Suid_Af rika, Transkei en
Bophuthatswana, Venda en Ciskei, en die Koninkryke van Lesotho en Swaziland”. The Government Printer, Pretoria.
WEINERT, H H, 1980.
The natural road construction materials of Southern Af rica. Academia, Cape Town.
AGES 32

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Technical Report: 2007 / 12 / 03 / DGSI

Document version 1.0

Detailed Engineering Geological Investigation in

Bigen Africa Services (PTY) Ltd on behalf of

Technical report: 2007 / 12 / 03 / DGSI

Detailed Engineering Geological Investigation in

Conducted on behalf of:

Mr. Le Roux Niemann

Di rec tors : SJ Pretorius (MD ) T N goe pe J A Myburgh JJ P V ivi er R Crosby

REPORT DISTRIBUTION LIST

Report no Date Version Status

1.2 Terms of reference

1.3 Scope of the investigation

1.4 Results of previous investigations

3.1 Location of the study area

Figure 1: Regional site locality (Google Earth)

Photo 1: General topography – very gentle to gentle slopes

Photo 2: General study area vegetation

3.6 Regional seismic intensity

4 NATURE OF THE INVESTIGATION

4.1 Desk study

4.2 Field work

4.3 Laboratory testing

5 REGIONAL GEOLOGICAL SETTING

5.1 Regional Stratigraphy

5.2 Prominent Geological Structures

5.3.1 Excavation of trial pits

Detailed trial pit profile logs are included as Appendix A.

Photo 3: Excavation of trial pit in progress

5.3.2 Generalised engineering geological parameters

• Rock and pedocrete outcrops

5.3.3 Generalised soil profile

The general soil conditions as observed on site is indicated in Photo 4 below.

5.4 Groundwater Occurrences

6.1 Engineering and Material Characteristics

Laboratory soil test data are included as Appendix B.

6.1.2 Soil test results: aeolian

Table 1: Summarised soil test results – Aeolian

6.1.4 Soil test results: pebble marker horizon

Table 3: Summarised soil test results – Pebble marker horizon

6.1.5 Soil test results: residual quartzite

Table 4: Summarised soil test results – Residual quartzite

6.2 Dynamic Cone Penetrometer testing

Photo 5: Dynamic Cone Penetrometer (DCP) test in progress

6.3 Slope Stability and Erosion

6.4 Excavation Classification – Bulk Services

The following additional comments on excavation of service trenches apply:

6.5 Impact of Geotechnical Character on Subsidy Housing Development

= Subsurface drainage / improved damp-proofing measures to be implemented

3. Difficulty of servicing of land due to slopes

= Difficulties associated with the provision of waterborne sanitation and the

5. Precautionary measures in sites underlain by dolomite/limestone

= Not applicable (pending verification in Phase 2 investigation)

= Masonry houses will require foundation design, building procedures and

7.2 Most favourable for residential de velopment

Zone A1 classifies as NHBRC Site Class C2-H1 – P(perched water table).