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Soilkraft cc
Reg no CK 96/08031/23
PO Box 73478
Lynnwood Ridge
0040
Tel : 012-9910426
Fax : 012-9912555
Email: [email protected]
GEOTECHNICAL CONDITIONS ON A PART OF PORTION 164 OF THE FARM KLIPFONTEIN 268JR : A REPORT FOR THE ESTABLISHMENT OF ROSSLYN EXTENSION 14
1 INTRODUCTION

Appointment : It is envisaged to establish a new urban development on a part of Portion 164 of the
farm Klipfontein 268-JR as Rosslyn Extension 14. To this end Soilkraft cc was appointed by Mr B
Falkson of Big Cedar Trading 22 (Pty) Ltd on 14 June 2006 to undertake a geotechnical survey
complying with the requirements of the Council for Geoscience
Reference 9.1
and other relevant
authorities. The purpose of such an investigation is to:


identify possible relevant geotechnical constraints;

make certain recommendations regarding the founding of structures and

to identify other factors that could possibly influence the future development of the area.
Reporting : Five printed and bound copies and the original of the report are supplied to the client.
An electronic copy of the entire report is also supplied to enable the client to adjust the site plans
to a scale convenient to him and to provide additional copies of the report, should it be required.
All printed drawings in the hard copies are in A2 or A4 format, and serve for illustrative purposes
only.

Scope of Investigation : The report reflects the geotechnical conditions as determined for township
development purposes. The report shall therefore under no circumstances be regarded as the
results of a detailed geotechnical investigation as far as zoning of individual stands, materials
utilization, depth of excavation or other related matters are concerned. These issues shall be
determined by purpose specific investigations and the results there of be evaluated by a suitably
qualified professional person.
2 AVAILABLE INFORMATION
The following sources of information were consulted :

1 : 50 000 geology map, 2528CA Pretoria published in 1973.

The document Materials Report for the Extension of an Existing Borrow Pit on the Farm Klipfontein
286-JK, issued by Soilkraft cc on behalf of Pave Show Civils on 9 June 2004.
3 SITE DESCRIPTION
3.1 Site Location
The property under discussion encompasses 141,4 hectare of land located approximately 25
kilometers to the northwest of the Tshwane city centre. It is situated on the southwestern perimeter of
the existing Rosslyn industrial area. The boundaries of the property are formed by provincial road
R566 to the south, Helium road to the north, Kitshoff Road to the east and a tributary of the Sandspruit
to the west.
Refer to the attached Figure 1 : Locality Plan.
3.2 Topography and Drainage
The property is located between 1273 meters sloping to 1235 meters above mean sea level. The
topography is characterized by the presence a flat, inland plain. It slopes from southeast to northwest
at approximately 2,9 %. The even land surface is abberated by small hillocks formed by outcrops of
norite and hortonolite-dunite.
Drainage takes place by means of surface sheetwash and becomes concentrated in the Sandspruit
just to the west of the property, or in the municipal stormwater disposal system.
3.3 Flora
The original flora of the land consisted of especially Acacia karoo trees and an undergrowth of
scattered grass. Some examples of various bushveld trees are still present on the property. Towards
the east natural flora have been removed for the present land utilization, but over the larger part of the
property natural vegetation has remained intact.
3.4 Climate and Weather Conditions
The site is located in an area with an approximate Weinert N-value of 2,4 and a Thornthwaite Moisture
Index between 0 and -20. Climatically the area may thus be described as subhumid. The importance
of this is that chemical weathering of rock material will take place, rather than mechanical breakdown
there of, resulting in the formation of active clays if the suitable parent material is available. Minerals
2
like amphiboles, pyroxenes and olivine are especially susceptible to such weathering.
The area receives summer rainfall at a mean annual precipitation of 664mm, generally in the form of
thunderstorms. The average maximum summer temperature of approximately 29,0°C occurs in
January. Winters are mild and frost is not common. The average minimum winter temperature of
4,0°C occurs in June.
4 EXISTING FACILITIES
At the time of investigation the larger part of the property was vacant. Some remains of old structures
are present in the western parts of the land. A soil removal operation for construction purposes, and
backfilling of the void with waste soil originating from construction projects, is in evidence on the
property.
Two major services traverse the property, namely an overhead Escom power transmission line close
to the western boundary and a Randwater pipeline just to the west of the soil removal operation. In
addition, the road reserve of the future PWV 7 is present along the western boundary of the land.
Site conditions are illustrated on the attached Photo 1 : Site Conditions.
5 SITE INVESTIGATION
5.1 Test Pitting

Trenching : For the purposes of the survey 68 test pits were excavated for this investigation. The
test pits were excavated with a various TLB’s provided by Pave Show Civils. The trenching was
undertaken from 11 July to 17 July 2006. The trenches were excavated up to refusal or at least
2000mm deep. The profiles of the trenches may be found in Addendum A to this report.

Auger Drilling : In some locations the vertical extent of the fill material exceeded the capacity of the
TLB. Eight test pits were thus drilled in the fill with a 700mm diameter auger. For this purpose a
Soilmech auger was made available by Gauteng Piling and the investigation done on 20 July
2006. The profiles of the auger holes may be found in Addendum B to this report.
The positions of the test pits are indicated on the site plans for this survey as contained in this report.
GPS grid references for the test pits are indicated on the profile sheets. The test pits were profiled by a
geotechnical engineer according to the guidelines of SAICE and SAIG
Reference 9.2
. For the benefit of the
non-geotechnical reader, these guidelines are summarized in the attached Table 1 : Soil Profiling
Parameters. The profile descriptions as per the test pits reflect the impressions created by the
pedological conditions and may sometimes be in slight variance with the results of the soil testing.
3
TABLE 1 : SOIL PROFILING PARAMETERS
CONSISTENCY : GRANULAR SOILS
SPT
N
<4
4-10
10-30
GRAVELS & SANDS
Generally free draining soils
Very
loose
Loose
Medium
dense
Dense
30-50
>50
Very
dense
Crumbles very easily when scraped with
geological pick. Requires power tools for
Small resistance to penetration by sharp
pick point. requires many blows by pick point
Considerable resistance to penetration by
sharp pick point.
Very high resistance to penetration by sharp
pick point. Requires many blows by pick point
for excavation.
High resistance to repeated blows of
geological pick. Requires power tools for
excavation.
CONSISTENCY : COHESIVE SOILS
DRY
DENSITY
(kg/m^3)
SPT
N
SILTS & CLAYS and combinations with
SANDS.
Generally slow draining soils
<1450
<2
1450-1600
2-4
Very
soft
Soft
1600-1750
4-8
Firm
1750-1925
8-15
Stiff
>1925
15-30
Very
stiff
Pick point easlily pushed in 100mm.
Easily moulded by fingers.
Pick point easlily pushed in 30mm to 40mm.
Moulded by fingers with some pressure.
Pick point penetrates to 10mm.
Very difficult to mould with fingers.
Slight indentation by pick point.
Cannot be moulded by fingers. Penetrated
by thumb nail.
Slight indentation by blow of pick point.
Requires power tools for excavation.
SOIL TYPE
SOIL TYPE
UCS
(kPa)
<50
50-125
125-250
250-500
500-1000
MOISTURE CONDITION
PARTICLE SIZE(mm)
Dry
No water detectable
Clay
<0,002
Slightly moist
Water just discernable
Silt
0,002-0,06
Moist
Water easily discernable
Sand
0,06-2,0
Very moist
Water can be squeezed out
Gravel
2,0-60,0
Wet
Generally below water table
Cobbles
60,0-200,0
Boulders
>200,0
SOIL STRUCTURE
COLOUR
Speckled
Mottled
Blotched
Banded
Streaked
Stained
Very small patches of colour <2mm
Irregular patches of colour 2-6mm
Large irregular patches 6-20mm
Approximately parallel bands of varying colours
Randomly orientated streaks of colour
Local colour variations : Associated with discontinuity
surfaces
Intact
Fissured
No structure present.
Presence of discontinuities, possibly cemented.
Slickensided
Very smooth, glossy, often striated discontinuity
planes.
Presence of open fissures. Soil break into gravel size
blocks.
Small scale shattering, very closely spaced open
fissures. Soil breaks into sand size crumbs.
Residual bedding, laminations, foliations etc.
Shattered
Micro shattered
Residual structures
ORIGIN
Transported
Residual
Pedocretes
Alluvium, hillwash, talus etc.
Weathered from parent rock, eg residual granite
Ferricrete, silcrete, calcrete etc.
DEGREE OF CEMENTATION OF PEDOCRETES
TERM
DESCRIPTION
UCS
(MPa)
Very weakly cemented
Weakly cemented
0,1-0,5
0,5-2,0
Cemented
Strongly cemented
Some material can be crumbled between finger and thumb. Disintegrates under knife blade to a friable state.
Cannot be crumbled between strong fingers. Some material can be crumbled by strong pressure between thumb and hard surface.
Under light hammer blows disintegrate to a friable state.
Material crumbles under firm blows of sharp pick point. Grains can be dislodged with some difficulty by a knife blade.
Firm blows of sharp pick point on hand-held specimen show 1-3mm indentations. Grains cannot be dislodged by knife blade.
2,0-5,0
5,0-10,0
Very strongly cemented
Hand-held specimen can be broken by single firm blow of hammer head. Similar appearance to concrete.
10,0-25
5.2 Materials Testing
Soil testing was done by the laboratory facilities of Civilab. The following soil tests were done :
4

Foundation indicators on samples of the residual and transported soils encountered during the
investigation.

California Bearing Ratio tests on samples of the in-situ soils.

Conductivity and pH determinations on samples of the in-situ soils.
The results of the soil testing are summarized in the attached Table 2 : Results of Soil Testing. The
results of the soil testing as received from the laboratory can be found in Addendum C.
6 DISCUSSION
6.1 Geology
The regional geology of the area is indicated on the attached Figure 2 : Regional Geology. This is an
extract of the geology map 2528CA Pretoria.
The property is located on the boundary of norite of the Main Zone, Rustenburg Layered Suite,
Bushveld Complex ; and hortonolite-dunite of the Bushveld Complex. From a stratigraphic viewpoint,
the hortonolite-dunite can be regarded as the younger material.
Norite is regarded as a plutonic, intrusive, basic, igneous rock. The mineral assemblage consists
predominantly of plagioclase and pyroxene. In an unweathered form norite can be described as a
coarse grained, light grey to dark grey and often speckled white, very hard rock. The individual mineral
grains can easily be discerned by the naked eye. Several outcrops and sub outcrops of norite were
encountered during the investigation.
Hortonolite-dunite is regarded as a plutonic, intrusive, ultra-basic, igneous rock. The mineral
assemblage consists predominantly of pyroxene and olivine. In an unweathered form hortonolitedunite can be described as a very coarse grained, dark grey to blue-black, rock. Platelets of biotite
were clearly discernable in the rock matrix during the investigation. It is hard to define the residual
hortonolite-dunite encountered during the investigation as rock. While the individual material particles
may be considered as rock, the matrix is very closely fractured and the materials encountered
behaved like soil rather than rock.
Under the given climatic conditions both the norite and the hortonolite-dunite are highly susceptible to
chemical decomposition and the formation of expansive clays as indicated in section 3.2 of this report.
The presence of fault zones is not indicated in the area. The attached Figure 3 : Site Geology allows
an overview of the geology of the property.
5
6.2 Soil Profiles
Natural soil profiles on site consist of colluvial argillaceous soil materials overlying the pebblestone
marker and various horizons of residual sand derived from the weathering of norite or hortonolitedunite. Fill materials encountered on site vary from clay to artificial materials. The following materials
were encountered during the survey :

Dark Red and Brown Colluvial Clayey Sand : A surface horizon of brownish colluvial, clayey sand
is present over the western part of the property. It covers the larger part of the property. The
vertical extent of the horizon is highly variable, ranging from only 200mm to more than 2000mm.
The soil matrix is typically desiccated and of medium dense consistency. The results of the
materials testing on samples of the colluvium indicate the grading modulus to vary between 0,12
and 0,14 ; and the plasticity index between 19 and 20. It contains 41% to 50% expansive clay. The
PRA materials classification is A-7-6(20 to 21). The material is regarded as moderately expansive.

Black Colluvial Sandy Clay : A surface horizon of black, colluvial, sandy clay was encountered in
the eastern parts of the property. Some isolated locations of the material were also encountered
close to the western perimeter of the property. This is the traditional black “turf” commonly present
in the area. Vertically the horizon extended between 400mm and 1400mm. The matrix of the clay
is typically fissured and slickensided, and of soft consistency. The results of the materials testing
on samples of the clay indicate the grading modulus to vary between 0,26 and 0,39 ; and the
plasticity index between 25 and 32. It contains 52% to 59% expansive clay. The PRA materials
classification is A-7-5(21 to 35). The material is regarded as moderately to highly expansive.

Pebblestone Marker : The pebblestone marker is the demarcating soils horizon between the
transported soil above it, and the residual soil below it. On site it was encountered mostly in the
western parts of the property underlying the red and brown colluvial clayey sand. Close to the soil
removal operation it is in several places exposed at the surface. It consists of red and brown
clayey sand, with a high content of medium coarse to coarse, black, magnetite gravel. The
presence of this gravel is quite a unique feature of the soil profile. Vertically the pebblestone
marker extended between 200mm and 800mm in the test pits. The material is regarded as non
expansive.

Residual Norite Clayey Sand : A well developed horizon of reddish clayey sand derived from the
weathering of norite is present in the western part of the property. It is usually encountered below
the pebblestone marker. The vertical extent of the horizon is highly variable, ranging from only
300mm to 1400mm. The soil matrix is typically intact to fissured and of medium dense
consistency. The results of the materials testing on samples of the sand indicate the grading
modulus to vary between 0,11 and 0,26 ; and the plasticity index between 22 and 24. It contains
32% to 65% expansive clay. The PRA materials classification is A-7-5(23) to A-7-6(25). The
material is regarded as moderately expansive.

Residual Fine to Coarse Norite Sand : This is the most widely distributed soils horizon on the
property, and it consists of fine sand to coarse sand. It is present directly underneath the colluvium
6
in the east, or underneath the residual clayey sand towards the west. The horizon extends
vertically up to bedrock. A gradual transition form soil to bedrock of norite is usually encountered,
associated with an improvement in consistency of loose and medium dense sand, to very dense
sand and bedrock of norite. The soil matrix is typically relic jointed. The results of the materials
testing on samples of the sand indicate the grading modulus to vary between 1,64 and 2,43 ; and
the plasticity index between 10 and 18. It contains 2% to 8% expansive clay. The PRA materials
classification is A-2-4(0) to A-2-7(0). The material is regarded as non-expansive.

Residual Hortonolite-dunite Clayey Sand : An irregularly developed horizon of reddish soil is
present as an upper residual soils horizon in the area underlain by bedrock of hortonolite-dunite.
As hortonolite-dunite is extremely susceptible to weathering, the soils occur as fine sand to clayey
sand, with some gravels of the more resistant minerals contained in the soil matrix. The vertical
extent of the horizon is highly variable, ranging from only 300mm to 1500mm. The soil matrix is
typically intact and of medium dense consistency. The results of the materials testing on a sample
of the sand indicate a grading modulus of 2,23 ; and a plasticity index of 15. It contains 4%
expansive clay. The PRA materials classification is A-2-7(0). The material is regarded as mostly
non-expansive, tending to slightly expansive.

Residual Coarse Hortonolite-dunite Sand : This is the lower most soil horizon in the area of
hortonolite-dunite, and it consists of dark yellow mottled dark blue stained light red, sandy gravel.
The horizon extends vertically up to bedrock. A gradual transition form soil to bedrock is usually
encountered, associated with an improvement in consistency with a diminishing extent of
discontinuities in the material matrix. The soil matrix is typically relic jointed. The results of the
materials testing on samples of the soil indicate the grading modulus to vary between 2,36 and
2,61 ; and the plasticity index between 13 and 23. It contains 3% to 5% expansive clay. The PRA
materials classification is A-2-7(0). The material is regarded as non-expansive.

Fill : Fill material is present in the northern and central parts of the property. The fill is imported
from construction sites to replace especially the residual hortonolite-dunite removed for
construction material. The fill consists mostly of bands of black sandy clay and clayey sand. Of
importance is that the fill can not be regarded as a material of homogenous composition, as it
contains abundant quantities of foreign matter like organic material, builders rubble, fibre glass,
discarded asbestos pipes etc. In the trenches and auger holes the vertical extent of the fill varied
between 400mm and 10900mm. Although the placement of the fill is an operation carried out with
circumspect, the fill can not be regarded as an engineered unit of material.
6.3 Hydrology

Perched Water : The investigation was conducted after a season of exceptional high rainfall, yet
perched water was encountered in test pit 59 only at a depth exceeding 2000mm. It is expected
that the presence of this perched water table may be associated with the presence of the spruit
close by. It must be stressed that the presence of perched water is a seasonal phenomenon and
the extent there of depends on precipitation, time of the year etc. In other words, it is possible that
7
in the middle of winter, much less perched water may be present in the area than in summer.
Considering the situation, it is expected that the extent of perched water occurrences on site will
be limited.

Permanent Water : Vegter
Reference 9.3
indicates the probability for drilling successfully for water in the
-1
area to be less than 40%, and the probability that such a borehole will yield more than 2ls to be
between 20% and 30%. Ground water is expected to occur at depths between 20 and 30 meters
in fractures restricted to a zone directly below ground water level.
6.4 Geotechnical Zoning
When discussing the engineering properties of the materials on site, it is important to bear the
following issues in mind :

Properties of Heave : Using the results of the soil testing in the parametric heave calculation
method as proposed by Van der Merwe
Reference 9.4
as per the RAFT software compiled by the CSIR,
unrestrained heave was calculated for all test pits where potentially expansive soil conditions
prevail. The calculated unrestrained heave was found to vary between 7,5mm and 42mm for these
test pits.

Properties of Settlement : Although the fill is compacted to some extent during the placing there
of, it is not an engineered operation, and the degree of compaction can not be guaranteed. The fill
further consists of materials of variable composition. Even if the fill may be in place for several
years, it is still subject to possible settlement if external stresses are applied. The extent of such
settlements can not be determined by simple methods of investigation, and is dependent on
material quality, compaction and vertical extent of the horizon. The fill is thus regarded as subject
to highly variable soil movements, but mostly settlement, due to applied external stresses.
The soil engineering classification of the area is in accordance with the guidelines of the
Reference 9.5
NHBRC
and is applicable to single storey structures of masonry construction. Based on the
principles as explained above, the following five geotechnical zones are distinguished :

Geotechnical Zone I : This is the central northern part of the property. It covers approximately
11,7% of the site and is considered as being of intermediate development potential. It is
characterized by a soil profile of reddish colluvial clayey sand overlying the various horizons of
residual hortonolite-dunite. The anticipated soil movement in the area consists of 7,5mm to 15mm
unrestrained heave. The area is consequently zoned as H1.

Geotechnical Zone II : This is the central western part of the property. It covers approximately
41,9% of the site and are considered as being of intermediate development potential. It is
characterized by a soil profile of reddish colluvial clayey sand overlying the pebblestone marker
and the various horizons of residual norite. The anticipated soil movement in the area consists of
15mm to 30mm unrestrained heave. The area is consequently zoned as H2.
8

Geotechnical Zone III : Three parcels of land, namely the southeastern, southwestern and
northwestern corners of the property are of similar engineering properties. These areas cover
approximately 29,7% of the site and is considered as being of intermediate development potential.
It is characterized by a soil profile of black colluvial sandy clay directly overlying residual norite
sand. The anticipated soil movement in the area consists of 30mm to 50mm unrestrained heave.
The area is consequently zoned as H3.

Geotechnical Zone IV : This is the small parcel of land close to the northwestern corner of the
property. It covers approximately 1,3% of the site and is considered as being of intermediate to
poor development potential. It is characterized by a soil profile of reddish colluvial clayey sand
overlying the various horizons of residual norite. However, it is distinguished from the remainder of
the site by the abundant presence of norite corestones, sub outcrops and outcrops of norite. The
anticipated soil movement in the area consists of 7,5mm to 15mm unrestrained heave. The area
is consequently zoned as P(Boulders)/H1. Conditions in this zone are illustrated on the attached
Photo 2.

Geotechnical Zone V : This is the area of land subject to soil removal and backfilling of the
excavated void. Initially it was considered to distinguish between the areas of excavation and
backfilling, but it is a continuous process and conditions can not be regarded as static. The
processes of excavation and backfilling are thus considered as one, and the area zoned as
P(Fill)/P(Mining). It covers approximately 15,4% of the site and is considered as being of poor
development potential. The estimation of possible soil movements is not regarded as applicable.
Conditions in this zone are illustrated on the attached Photo 3.
The geotechnical zoning of the site is indicated on the attached Figure 4 : Geotechnical Zoning Map.
6.5 Construction Material
Most of the materials encountered on the property are not suitable to be utilized for road construction.
The following conditions prevail :

Transported Soils : None of the transported soils are suitable to be utilized as material for road
construction.

Argillaceous Residual Soils : These materials are the upper horizons of residual norite and
hortonolite-dunite with a high clayey content. The materials are not suitable to be utilized for road
construction.

Residual Sand Derived from Norite : The results of the CBR and indicator testing indicate the
samples tested to be of G7 to G9 quality as per TRH classification. These materials may thus be
regarded as suitable for the construction of road layerworks up to upper selected layer for lightly
trafficked roads
Reference 9.6
. The material is known to improve with depth to G5 quality, and is a
sought after source of gravel for road construction.
9

Residual Sandy Gravel Derived from Hortonolite-dunite : The results of the CBR and indicator
testing indicate the samples tested to be of G6 to G7 quality as per TRH classification. These
materials may thus be regarded as suitable for the construction of road layerworks up to upper
selected layer for lightly trafficked roads as above.
6.6 Conditions of Excavation

Geotechnical Zone I : It is expected that it will be possible to excavate to a depth of at least
2000mm without encountering undue occurrences of hard rock. The sidewalls of excavations are
expected to be stable.

Geotechnical Zone II : It is expected that it will be possible to excavate to a depth of at least
1500mm without encountering undue occurrences of hard rock. The sidewalls of excavations are
expected to be stable. Corestones of norite may be present in the soil profile.

Geotechnical Zone III : It is expected that it will be possible to excavate to a depth of at least
1500mm without encountering undue occurrences of hard rock. The sidewalls of excavations are
expected to be stable. Corestones of norite may be present in the soil profile. Conditions of
excavation can generally be regarded as clayey.

Geotechnical Zone IV : It is expected that depth of excavation will be limited to less than 1000mm
prior to encountering bedrock of norite. Abundant corestones of norite are contained in the soil
profile. The sidewalls of excavations are expected to be stable.

Geotechnical Zone V : A typical description of conditions of excavation can not be provided for this
zone. Conditions of shallow excavation with early refusal of large blocks of concrete may occur,
likewise was it possible to penetrate with the 700mm auger to a depth of nearly 11 meters. In a
similar way can sidewalls of excavations be considered as stable in the argillaceous material, but
excavations in loose builders rubble may collapse.
6.7 Soil Corrosivity
When discussing soil corrosivity, it is important to consider the guidelines as proposed by
Evans
Reference 9.7
. The corrosivity of a soil towards buried, exposed, metallic surfaces is dependent on
the following properties of the soil :

Electrical conductivity;

Chemical properties of the soil;

Ability of the soil to support sulphate reducing bacteria and

Heterogeneity of the soil.
The tests carried out for the compilation of this report must be considered as indicative of the soil
conditions only. The pH of a soil gives an indication of potential acid related problems. Should the soil
10
pH be less than 6,0, corrosion may take place ; and should the pH be less than 4,50, the problem of
-1
corrosion may be serious. If the conductivity of the soil is less than 0,1mScm , corrosivity is generally
not a problem. However, the corrosion potential of the soil increases with an increase in conductivity.
-1
Should the conductivity of the soil exceed 0,5mScm , the soil can be regarded as very corrosive.
Should exposed metal pipes pass from argillaceous soils to arenaceous soils or vice versa,
electrochemical cells are set up due to the different rates of oxygen diffusion of the soils. Sulphate
reducing bacteria is usually present under anaerobic conditions, that is, typically saturated or
waterlogged clays.

Chemical Properties of the Soil : The results of the chemical testing of the soil sampling indicate
that none of the soils can be regarded as corrosive due to the inherent acidity there of. However,
all soils can be regarded as corrosive due to the content of soluble salts.

Heterogeneity of the Soil : There is a transition from mostly argillaceous soil to arenaceous soil on
the interface between the transported and residual soils. Electrochemical cells can thus be set up
due to the different rates of oxygen diffusion of the soils along this boundary, resulting in
chemically corrosive soil conditions.

Water Logged Soils : Conditions of water logged soils may occur along the western perimeter of
the property in the vicinity of the spruit.
6.8 Cemetery Sites
There are no cemeteries or graves on the site. Taking the guidelines of Fischer
Reference 9.8
into account,
Zones I, II and II may provisionally be regarded as suitable for the development of a cemetery site.
This excludes areas close to the spruit.
6.9 Seismicity
Reference 9.9
Kijko
indicates the annual probability for an earthquake with intensity of 4,2 on the Modified
0
Mercalli Scale to occur in the area to be less than 10 ; and with an intensity of 7,1 to occur the
-3
probability is 10 . A 10% probability exists that an earthquake with Peak Ground Acceleration of
0,12g to 0,16g may take place once in 50 years.
To put the above information into perspective, Table 3 : Earthquake and Magnitude and Intensity, is
attached to this report.
6.10 Other Considerations

Dolomite Stability : The site is not subject to instabilities due to the presence of dolomite.

Historic Monuments : There are no historic monuments on the site.
11
TABLE 3 : EARTHQUAKE MAGNITUDE AND INTENSITY
MODIFIED MERCALLI INTENSITY
INTENSITY SCALE
DESCRIPTION
RICHTER SCALE
MAGNITUDE
RADIUS OF
PERCEPTIBILITY (km)
3.5 to 4.2
3 to 24
4.3 to 4.8
24 to 48
I
Instrumental
Detected only by seismography
II
Feeble
Noted only by sensitive people
III
Slight
Like the vibrations due to a
passing lorry. Felt by people at
rest, especially on upper floors
IV
Moderate
Felt by people while walking.
Rocking of loose objects,
including vehicles
V
Rather
strong
Felt generally ; most sleepers
are awakened and bells ring
VI
Strong
Trees sway and suspended
objects swing ; damage by
overturning and flling of loose
objects
4.9 to 5.4
48 to 112
VII
Very strong
General public alarm ; walls
crack ; plaster falls
5.5 to 6.1
110 to 200
VIII
Destructive
Car drivers seriously disturbed;
masonry fissured ; buildings
damaged
6.2 to 6.9
200 to 400
IX
Ruinous
Houses collapse ; pipes break
X
Disasterous
Ground cracks badly ; buildings
destroyed ; railway lines bent ;
landslides on steep slopes
7.0 to 7.3
400 to 700
XI
Very
disasterous
Few buildings remain standing;
bridges destroyed ; all services
out of action ; great landslides
and floods
7.4 to 8.1
400 to 700
XII
Catastrophic
Total destruction ; objects
thrown into the air; ground
rises and falls in waves
>8.1
400 to 700
12

Undermining : The area is not subject to undermining.
7 CONCLUSIONS
Based on geotechnical considerations the area is partially suitable for urban development. The
following must be taken into account:

Geology : The property is located on norite and hortonolite-dunite of the Bushveld Complex.

Soil Profiles : The general, natural soil profile on the property consists of transported argillaceous
material overlying the pebblestone marker and argillaceous residual material, becoming
arenaceous soil at depth. Areas of borrow pitting and fill have altered this soil profile.

Groundwater : It is expected that seasonal perched water will not be present on site, except along
the western perimeter in the vicinity of the spruit.

Founding Conditions : The property is divided into the following geotechnical zones : H1 covering
11,7% of the land, H2 covering 41,9% of the land, H3 covering 29,7% of the land, P(Boulders)/H1
covering 1,3% of the land ; and P(Fill)/P(Mining) covering 15,4% of the land.

Conditions of Excavation : Conditions of excavation vary across the property. It is generally
possible to excavate to a depth of 1500mm, except in Zone P(Boulders)/H1, where abundant
corestones and bedrock of norite is present close to the surface. While the fill may generally be
stable in excavations, the condition there of must be monitored on an ad-hoc basis to ensure the
stability there of.

Materials Utilization : The residual norite sand and residual hortonolite-dunite gravel are suitable to
be used for road construction up to selected layer level. The quality of the norite improves with
depth.

Soil Corrosivity : Soil corrosivity is a factor to consider in the area.

Historic Monuments : There are no historic monuments on the site.

Cemetery Sites : There are no cemeteries or graves on the site. Parts of the property are
provisionally regarded as suitable for cemetery site development.

Dolomite Stability : The site is not subject to instabilities due to the presence of dolomite.

Undermining : The area is not subject to undermining, but large-scale excavation of surface soils
has not taken place for road building purposes.

Seismicity : The annual probability for an earthquake with intensity of 4,2 on the Modified Mercalli
0
Scale to occur in the area is less than 10 ; and with an intensity of 7,1 to occur the probability is
-3
10 . A 10% probability exists that an earthquake with Peak Ground Acceleration of 0,12g to 0,16g
may take place once in 50 years.
13
8 RECOMMENDATIONS
8.1 Road Construction
The residual norite sand and residual hortonolite-dunite can be stockpiled for the construction of road
layerworks up to selected layer level. Although these materials can be regarded as suitable for road
construction, they are usually located at such depth in the soil profile that it will not be possible to
incorporate them as in-situ material into the pavement prism. It thus appears as if all materials for road
construction will have to be obtained from commercial sources.
Over and above these proposals, the following must be considered to ensure the long-term
serviceability of the road structure :

Geotechnical Zones II and III : The argillaceous soil may be removed and the pavement prism
undercut to minimize the influence of expansive soil on the pavement prism.

Geotechnical Zone IV : The presence of boulders, bedrock at shallow levels and outcrops may
require careful horizontal alignment of the access ways to minimize construction costs.

Geotechnical Zone V : Conditions not conducive for road construction are encountered in this
zone. Specialist knowledge in pavement design must be obtained in this area. Pavement design
may include extensive undercutting, dynamic compaction or the provision of pioneer layers.
8.2 Preliminary Proposals for Founding and Construction
As this document serves as a guideline for the purposes of township development, it is proposed that
the site of each structure be investigated prior to construction regarding the conditions of founding. A
competent person should evaluate the results of such an investigation to ensure that there is no local
discrepancy on site between the conditions actually encountered and those detailed in this document.
The recommendations below are given in accordance with the existing guidelines
Reference 9.10
. For the
purposes of this document and township development the following alternatives are recommended
regarding structural design :
 Geotechnical Zone H1 : Modified normal construction procedures of superstructures is proposed.
Construction of the superstructure must include articulation joints at some internal and all external
doors, light reinforcement in the masonry, site drainage and service/plumbing precautions.
Foundations should be designed to accommodate unrestrained heave of up to 15mm. The use of
reinforced strip foundations is proposed.
 Geotechnical Zone H2 : Modified normal construction procedures of superstructures is proposed.
Construction of the superstructure must include articulation joints at some internal and all external
doors, light reinforcement in the masonry, site drainage and service/plumbing precautions.
14
Foundations should be designed to accommodate unrestrained heave of up to 30mm. Either
reinforced strip foundations or reinforced concrete rafts may be considered. As an alternative, the
option of soil replacement rafts may be considered. The excavations for a soil replacement raft
shall extend through the argillaceous soil into the inert norite derived soil. Such excavation must be
backfilled with compacted material of G5 quality.
 Geotechnical Zone H3 : Modified normal construction procedures of superstructures are proposed.
Construction of the superstructure must include articulation joints at some internal and all external
doors, light reinforcement in the masonry, site drainage and service/plumbing precautions.
Foundations can consist of reinforced concrete rafts or soil replacement rafts. The excavations for
a soil replacement raft shall extend through the argillaceous soil at least 300mm deep into the
residual norite sand, or to 2000mm deep maximum. Such excavation must be backfilled with
compacted material of G5 quality. Reinforced concrete raft foundations shall be designed to
accommodate 50mm unrestrained heave.
 Geotechnical Zone P(Boulders)/H1 : Modified normal construction procedures of superstructures
are proposed. Construction of the superstructure must include articulation joints at some internal
and all external doors, light reinforcement in the masonry, site drainage and service/plumbing
precautions. Due to the dissimilarity in material characteristics in the area, each stand shall be
evaluated by a competent person and a foundation design be done based on his
recommendations. As a minimum it is foreseen that foundations should be designed to
accommodate unrestrained heave of up to 15mm. However, provision must be made for the slope
across the area, presence of boulders and rock outcrops. The structures may thus be founded by
reinforced strip foundations carrying high plinths with reinforced cavity walls, or similar solutions.
 Geotechnical Zone V : It is recommended that this zone be set aside as public open space.
However, it is possible to develop it on an economical basis, the site for each strucutre shall be
investigated on an individual basis. At this stage it is foreseen that strucutres may be founded by
variations of pile designs, making provision for uplift due to the clay and considering the presence
of large, foreign objects in the fill.
As far as the choice between reinforced concrete rafts and soil replacement rafts is concerned, the
financial break even point between soil replacement rafts and concrete rafts is between 800mm and
1000mm of expansive soil : Should the thickness of the expansive soil horizon be less than this figure,
it is usually more cost effective to excavate and replace the expansive soil with a controlled fill ; and
should the expansive horizon be thicker than this figure, it is cheaper to use a reinforced concrete raft
as founding system for the future structure.
The decision of which founding system to use is the responsibility of the consulting engineer. The
above proposals are given in good faith, but the final decision must be made based on financial
constraints and experience of similar conditions.
15
The anticipated soil movements, soil zoning and foundation alternatives are summarized in the
attached Table 4 : Foundation Design, Building Procedures and Precautionary Measures. Detailed
proposals for foundation and superstructure construction as approved by the Joint Structural Division
of SAECI and IstructE and published by the NHBRC, are attached as Addendum D.
8.3 Conditions of Excavation
The anticipated depths of excavation and slope stabilities are clearly discussed in section 6.6 of this
report. Cognizance must be taken of these guidelines. Under the heading of “Conditions of
Excavation”, SABS 1200 allows, amongst others, the following :

Soil : It is proposed that all soils be considered as soft to excavate, becoming very dense with
depth.

Rock : Where rock is encountered, it will be hard and provision must be made for hard excavation
or blasting.

Boulder Excavation : The presence of boulders and corestones is expected across the entire site,
and especially in zone IV. Provision must be made for the removal of such materials.

Fill : The fill contains foreign matter and special precaution must be taken with excavations in the
material. The stability of slopes in the fill must be monitored at all times.
8.4 Seismicity
The guidelines of the National Housing Board
Reference 9.11
indicate the level of seismicity of the area to
be within acceptable limits. In terms of seismicity the development potential of the area is regarded as
favourable.
8.5 Corrosive Soil
Conditions of corrosive soil prevail on the site. It is therefore recommended that non-metallic
subsurface materials be used for services, or, if the use of metallic materials cannot be avoided, the
materials must be coated or protected against corrosion.
9 SOURCES OF REFERENCE
9.1 South African Institute of Engineering Geologists : Guidelines for Urban Engineering Geological
Investigations, pages 2 to 8, published in 1997.
9.2 SAIEG-AEG-SAICE : Guidelines for Soil and Rock Logging – Proceedings of the 1990
Geoterminology Workshop.
16
9.3 Vegter JR : An Explanation of a Set of National Ground Water Maps, published by the Water
Research Commission, in August 1995.
9.4 Van der Merwe D : The Prediction of Heave from the Plasticity Index and Percentage Clay
Fraction of Soils, published in the Civil Engineer in South Africa, June 1964, pages 103 to 107.
9.5 NHBRC : Home Building Manual Part 1 & 2, Revision 1, page 18, published in February 1999.
9.6 Committee of Urban Transport Authorities : Structural Design of Urban Roads (Draft UTG 3), page
68, published in 1993.
9.7 Evans UR : The Corrosion and Oxidation of Metals, published by Edward Arnold in 1971.
9.8 Fischer GJ : The Selection of Cemetery Sites in South Africa, published by the Council of
Geoscience.
9.9 Kijko A et al : Probabilistic Peak Ground Acceleration and Spectral Seismic Hazard Maps for South
Africa, Report 2003-0053 by the Council for Geoscience.
9.10 SAICE/IstructE : Code of Practice for Foundations and Superstructures for Single Storey
Residential Buildings of Masonry Construction, Tables 5 to 7, published in August 1995.
9.11 National Department of Housing : Geotechnical Site Investigations for Housing Developments –
Generic Specifications GFSH-2, table 3 page 27, published in September 2002.
FJ Breytenbach, Pr Eng
21 September 2006
For Soilkraft cc
17