GEO PROJECT
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DECLARATION
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INTRODUCTION
SITE DESCRIPTION
The approximate location of the site is 29°52'39.3"S (-29.8775700°)
26°24'42.5"E (26.4118000°).
Lying even further east of Pretoria than Silver Lakes, the site is situated right out in the 'country', a
burgeoning neighbourhood that started with a series of smallholdings and country estates and is fast
becoming something of a suburb, with beautiful views and any number of hiking opportunities.
Spatially heterogeneous landscapes provide larger habitat variations than a spatially homogenous
landscape, and thus the importance of ridges as biodiversity hotspots cannot be replicated. Spatially,
the orientation of ridges is important. The orientation of the ridge in relation to the sun will influence
the vegetation composition on the different sides of the ridge, since the duration of daylight varies
according to the spatial aspect of the ridge. The orientation of the ridge will also influence the rainfall
pattern across the ridge. The geology and erodibility of the soils, as well as the slope, will influence
the water velocity, retention and nutrient leaching rates.
Proposed site
CLIMATIC AND TOPOGRAPHIC DATA
At Pretoria, the summers are long, warm, and partly cloudy and the winters are short, cold, dry, and
clear. Over the course of the year, the temperature typically varies from 42°F to 83°F and is rarely
below 36°F or above 90°F.Based on the tourism score, the best times of year to visit Pretoria for warmweather activities are from late February to mid-May and from mid-August to late October.
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Average Temperature at Pretoria
The warm season lasts for 5.9 months, from September 24 to March 20, with an average daily high
temperature above 79°F. The hottest month of the year at Pretoria is January, with an average high
of 83°F and low of 64°F. The cool season lasts for 2.1 months, from May 27 to July 31, with an average
daily high temperature below 69°F. The coldest month of the year at Pretoria is June, with an average
low of 43°F and high of 66°F.
Clouds
At Pretoria, the average percentage of the sky covered by clouds experiences significant seasonal
variation over the course of the year. The clearer part of the year at Pretoria begins around March 28
and lasts for 6.4 months, ending around October 10. The clearest month of the year at Pretoria is July,
during which on average the sky is clear, mostly clear, or partly cloudy 92% of the time. The cloudier
part of the year begins around October 10 and lasts for 5.6 months, ending around March 28. The
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cloudiest month of the year at Pretoria is November, during which on average the sky is overcast or
mostly cloudy 36% of the time.
Precipitation
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of
wet days at Pretoria varies very significantly throughout the year. The wetter season lasts 5.5 months,
from October 17 to April 1, with a greater than 26% chance of a given day being a wet day. The month
with the wet days at Pretoria is December, with an average of 15.6 days with at least 0.04 inches of
precipitation. The drier season lasts 6.5 months, from April 1 to October 17. The month with the
fewest wet days at Pretoria is July, with an average of 0.4 days with at least 0.04 inches of
precipitation. Among wet days, we distinguish between those that experience rain alone, snow alone,
or a mixture of the two. The month with the most days of rain alone at Pretoria is December, with an
average of 15.6 days. Based on this categorization, the most common form of precipitation throughout
the year is rain alone, with a peak probability of 52% on December 18.
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Rainfall
To show variation within the months and not just the monthly totals, we show the rainfall accumulated
over a sliding 31-day period centered around each day of the year. Pretoria experiences significant
seasonal variation in monthly rainfall. The rainy period of the year lasts for 8.1 months, from
September 9 to May 11, with a sliding 31-day rainfall of at least 0.5 inches. The month with the most
rain at Pretoria is January, with an average rainfall of 3.8 inches. The rainless period of the year lasts
for 3.9 months, from May 11 to September 9. The month with the least rain at Pretoria is July, with an
average rainfall of 0.1 inches.
TOPOGRAPHY OF THE PROPOSED AREA
For the purposes of this report, the geographical coordinates of Pretoria are -25.733 deg latitude,
28.183 deg longitude, and 4,327 ft elevation. The topography within 2 miles of Pretoria contains
significant variations in elevation, with a maximum elevation change of 574 feet and an average
elevation above sea level of 4,284 feet. Within 10 miles contains significant variations in elevation
(1,342 feet). Within 50 miles contains very significant variations in elevation (2,927 feet). The area
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within 2 miles of Pretoria is covered by artificial surfaces (100%), within 10 miles by artificial surfaces
(69%) and grassland (13%), and within 50 miles by grassland (34%) and cropland (26%). The most
elevated portion of the area is situated along its southern boundary. The country displays a gradual
regional slope to the north, the continuity of which is locally broken by hills and ridges of resistant
rocks such as the chert bands in the upper Dolomite Series and the quartzite bands of the Pretoria
Series. Prominent quartzite ridges are the Magaliesberg and Witwatersberg. The southern portion of
the area approaches the Highveld in its characteristics, and forms undulating to hilly country. The
western, central and eastern portions largely fall in the Middleveld and are also called "Bankeveld".
This is characterized by roughly parallel hills, ridges and escarpments with longitudinal valleys
between. The northern portion forms part of the Bushveld, which in this area is occupied by
comparatively flat to undulating country, the monotony of which is relieved by ridges of granophyre
and gabbro. The "Pyramid" line of hills increases in height above the surrounding flats from east to
west, i.e. from 120 m at Bon Accord to 300 m at Kareepoortberg.
VEGETATION
The landscape is highly variable, with extensive sloping plains and a series of ridges slightly elevated
over undulating surrounding plains. The vegetation is species-rich, wiry, sour grassland alternating
with low, sour shrubland on rocky outcrops and steeper slopes. Most common grasses on the plains
belong to the genera Themeda, Eragrostis, Heteropogon and Elionurus. A high diversity of herbs, many
of which belong to the Asteraceae, is also a typical feature. Rocky hills and ridges carry sparse
(savannoid) woodlands with Protea caffra subsp. caffra, P. welwitschii, Acacia caffra and Celtis
africana, accompanied by a rich suite of shrubs among which the genus Searsia (especially S.
magalismonata) is prominent.
FIELD AND LAB WORK PROPOSAL
Field testing is done at the project site. Certified professionals carry out field testing services for
various construction projects that can include roadways, bridges, utility projects, airports, and building
developments. Typically, soil sampling is a method of removing sub-surface earth materials. These soil
samples can be evaluated in the field or taken back to the lab for further testing. The technicians check
for moisture and compaction, which will affect the building's foundation.
It seems obvious, but it is critical to have a strong foundation, without issues, before construction
begins. This includes the ground to be built upon and the materials used to build the structure.
Material testing ensures that the project will be successful before the foundation is laid. Without this
testing, builders and engineers will not be aware of the quality of the sub-surface and materials and
whether they will meet the project's requirements. Other types of field testing include:
Soil and Aggregate Sampling and Testing
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Compaction and Density
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Bearing Ratio
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Permeability Testing
Lab testing is when material samples are taken back to an off-site location or lab to review and analyze.
Don't confuse this with product testing, which is also done in a lab and involves reviewing, testing, and
providing reports on finished products, such as doors, windows, curtainwalls, and roofing products.
Pre-testing finished products and how they perform in a lab does not guarantee how well they will
perform in the field, especially if the construction materials that support the finished products have
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not been properly tested and inspected. Lab testing on material samples such as soil, asphalt,
aggregate, concrete, and masonry taken from the field site is a reliable method to provide detailed
analysis on the materials, ensuring that the materials on a job site will not cause any project-related
issues. Lab tests can also be performed if the field testing results prove inconclusive or a more detailed
analysis is needed.
Unconfined Compression Test on Rock
The unconfined compression test is the type of laboratory test that is used to determine the strength
of rocks. Unconfirmed compressive strength of rocks may be defined as the maximum axial
compressive stress that the specimen can withstand under zero confining stress. This test is used
extensively in geotechnical designs and construction.
Triaxial Compression Test on Rock
Triaxial Compression Test may be defined as the type of compression test in which the cylindrical rock
specimen is encased in an impervious membrane and is subjected to a confining pressure and finally
loaded axially to failure. It is very similar to the triaxial compression test carried out on the soil. Since
the test procedure involves the application of lateral pressure and deviator stress thus a special type
of equipment is necessary for encompassing the large stresses. In general, the specimen of rock is first
subjected to confining pressure then gradually the deviatoric stress is applied to keep the confining
pressure constant. The specimen is usually enclosed in a jacket that is made up of polyurethane which
is oil resistant.
Ultrasonic Testing
Is used to determine the pulse velocities of compression and shear waves in intact rock and the
ultrasonic elastic constants of isotropic rock. Ultrasound waves are transmitted through a carefully
prepared rock specimen. The ultrasonic elastic constants are calculated from the measured travel time
and distance of compression and shear waves in a rock specimen. The ultrasonic evaluation of elastic
rock properties of intact specimens is useful for rock classification purposes and the evaluation of
static and dynamic properties at small strains (shear strains < 10-4 %). Older equipment only provides
ultrasonic P-waves measurements, while new designs obtain both P- and S-wave velocites. When
compared with wave velocities obtained from field geophysical tests, the ultrasonics results provide
an index of the degree of fissuring within the rock mass. This test is relatively inexpensive to perform
and is nondestructive, thus may be conducted prior to strength testing of intact cores to optimize data
collection
ASSUMPTIONS AND LIMITATIONS
Even though every care is taken to ensure the accuracy of this report, environmental assessment
studies are limited in scope, time and budget and therefore largely subjective. Discussions and
proposed mitigations are to some extent made on reasonable and informed assumptions, built on
bone fide information sources, and deductive reasoning and personal experience. The interpretation
of the overall geotechnical conditions along the powerline route is based upon a review of available
information on the project area. Subsurface and geotechnical conditions have been inferred at a
desktop level from available information, past experience in the project area and professional
judgement. The information and interpretations are given as a guideline only and there is no
guarantee that the information given is totally representative of the entire area in every respect.
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OHS REQUIREMENTS
The Site Investigation Code of Practice establishes a standard of "acceptable engineering practice" to
assist the construction industry (client, project manager, consultant, contractor) in the planning,
design and execution of geotechnical site investigations in southern Africa. the following legislation
should be considered:
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Mine Health and Safety Act, No. 29 of 1996.
National Water Act, No. 36 of 1998.
Occupational Health and Safety Act, No 85 of 1993.
Housing Consumers Protection Measures Act, No. 95 of 1998.
National Building Regulations and Building Standards Act, No. 103 of 1977.
Natural Scientific Professions Act, No. 106 of 1993.
Engineering Professions Act, No. 114 of 1990.
Minerals Act, No. 50 of 1991.
STOME WATER DRAINAGE CONCEPTS
All the main streams flow to the north in conformity with the general "lope. They are the Crocodile,
Magalies, Jukskei, Hennops, Apies and I'ienaars Rivers and their tributaries. The main streams and
some of their tributaries are frequently undeflected in their courses by prominent ridges and locally
they have incised steep gorges or valleys in the resistant beds at right angles or oblique to the strike.
Some of the gaps in the ridges have been predetermined by faults, for instance on Zwavelpoort 373
JR, Tiegerpoort 371 JR and at Hartbeespoort Dam, but most of the steep valleys formed by the
Crocodile, Hennops and Skeerpoort Rivers bear no relationship to pre-existing faults. The drainage has
evidently been predetermined by the erosion pattern of the Karoo beds prior to denudation; in other
words, the drainage is superimposed on the pre-Karoo structures. Subsequent younger drainage by
longitudinal streams on less resistant shaly beds has given rise to the formation of broad valleys
between the ridges. Resequent tributaries have incised the dip slopes on the northern side of the
ridges, and the steeper slopes to escarpments on the southern side. Some of these streams have cut
across the crest line and smaller catchment areas have been formed on the other side. The erosional
power of these streams is evidently not caused by the supply of water from the catchment areas, but
by cutting and lowering of their base levels. A more advanced stage is displayed by the Skeerpoort
River and the upper course of the Magalies River, which during the process of back cutting have
reached the dolomite. Sources of underground water in the dolomite were tapped, which increased
the erosional power of the streams and their tributaries. Stream capture may also have played a role;
for instance the former course of the Magalies River probably more or less coincided with the
Swartspruit, whereas its present course may have been originally a tributary, which cut backward on
Zeekoehoek 509 JQ and Doornbosch 508 JQ until it captured the upper course of the Swartspruit north
of Magaliesburg. Rejuvenation of the entire stream pattern and a general lowering of the main base
levels probably took place during uplift of the continent in late post-Karoo times. The formation of
local base levels is rather exceptional, but well illustrated by the Hennops River. The gradient of the
latter between Wierda Bridge and the upper chert zone in the dolomite is 1:277 and between the
chert zone and the Crocodile River 1:181. The gradients of the Swartbooispruit and Rietspruit,
however, decrease downstream in a normal way_
UNDERGROUND WATER RESOURCES
Pretoria owes its initial development to the so-called IIfountains" or springs that rise in the dolomite
south of the city. Even today about 20% of the city's water requirements of some 200 000 mJjday are
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obtained from dolomite springs in the Fountains, Kafferspruit and Sterkspruit valleys. The rest is
supplied by the Rand Water Board from the Vaal River catchment on the other side of the continental
divide. Because of the duplication of outcrops by a strike overthrust there are two bodies of dolomite
south of Pretoria separated by rocks of the Pretoria Series. The lowest part of the outcrop of the
eastern body of dolomite lies in the Kafferspruit valley upstream of the Rietvlei Dam and there
groundwater overflows from the dolomite at several widely separated springs. The exact position of
each spring is probably determined by the disposition of the various dykes that occur there in relation
to the topographical relief. The western body of dolomite is divided by the Pretoria dyke into an
eastern and a western part and, as this dyke is the locus of the deep ,Fountains valley drained by the
headwater of the Apies River, the lowest points of the outcrops of both parts of the dolomite are on
either side of the Pretoria dyke in this valley as indicated by the geological map after Cilliers (1953),
figure 5. Overflow of groundwater from the eastern part of the western dolomite body at the
Sterkfontein springs near Olifantsfontein also contributes to the Pretoria city's supply. Available data
on groundwater in the Pretoria area are presently (1975) being assembled and processed (and will
form the subject of a proposed separate Geological Survey publication).
GEOLOGY OF THE AREA
The Donkerhoek batholith comprises mainly metaluminous to strongly peraluminous granites.
Numerous late-tectonic dykes, pegmatites, and aplites occur also (Clemens et al. 2017; Miller 2008).
The Donkerhoek batholith also includes minor volumes of magnesian, metaluminous to peraluminous
calc-alkaline rocks, such as quartz diorites, monzogranites, granodiorite, and tonalite (Clemens et al.
2017; McDermott et al. 1996). The Kurikaub granodiorites and tonalites and the Nomatsaus granites
are part of this suite. Exposures of the rock types are generally in the form of few isolated small-scale
domes and flat-lying outcrops near river banks. Textures of the Nomatsaus granite are equigranular
with generally no preferred orientation of the rock-forming minerals. Although outcrop evidence is
restricted to small-scale domes at the river bank, the intrusion appears structureless. Enclaves are
absent. The host rocks of the Nomatsaus intrusion are other granites of the Donkerhoek batholith,
however, due to coverage of the area with gravel and sometimes grass beds contacts are not exposed.
PROBLEM SOILS IN THE AREA
Field observation and laboratory test can be useful to identify problematic soils. Some properties of
soils such as dry density and liquid limit are helpful to estimate collapsibility potential of soils. In this
regard, it was done a series laboratory tests to evaluate the collapsibility rate. Problem soils can be
naturally occurring or man-made soils. This includes soils that have been displaced naturally or by
man. Problem soils can give rise to many geotechnical difficulties including inadequate bearing
capacity, the potential for unacceptable settlements and slope instability. There are many types of
problem soils, some of the most noteworthy being expansive soils, collapsible soils, soft clays and
dispersive soils. Most of the damage to structures in South Africa is related to soil characteristics, with
expansive and collapsing soils causing the most problems. In addition to the well documented historic
concerns dealing with specific problem soils, recent encounters with significant situations have
highlighted the need for a comprehensive documentation on the role of remote sensing and GIS
technologies for mapping, characterizing and monitoring problem soils in South Africa. In Gauteng,
but more specifically in Tshwane, the primary causes of sinkholes are concentrated stormwater
ingress, especially after heavy rains, or leaking water-bearing infrastructure. Decline of water levels drought, groundwater pumping (wells, quarries, mines) Disturbance of the soil - digging through soil
layers, soil removal, drilling. Point-source of water - leaking water/sewer pipes, injection of water.
Colluvium and Alluvium
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Colluvium is an all-embracing term that includes all soils on hill or mountain slopes that have moved
down-slope under the influence of gravity and un-concentrated surface wash. Coarse colluvium
includes talus, slide debris and colluvial gravel whilst fine grained hill wash consists of clayey or silty
composition with variable amounts of sand. Slope instability is the main concern on talus slopes whilst
silty or clayey hill wash exhibit potential expansive characteristics with soil moisture fluctuations or
might be potentially collapsible and compressible when subject to load. Alluvial deposits result from
the transportation and deposition of sediment by rivers. Within the channel sediment accumulations
are of limited areal extent and include transitory bedload deposits and alluvial islands, formed initially
of coarse sediment and subsequently overlain by finer material. Along the margins of channels there
are lateral deposits in the form of discontinuous bars in straight channels, or point bars on the convex
of meanders. Accumulations of sediment in aggrading or abandoned channels are termed channel
fills.
ENVIRONMENTAL CONSIDERATIONS
Environmental considerations include strategies, development guidelines and land use plans related
to greenspaces, derelict and contaminated land, nature conservation and biodiversity, flooding, air
and water quality, green design and climate change. The impact of the development from a
geotechnical perspective will be restricted to the removal and displacement of soil, boulders and
bedrock referred to in this report as “subsoils”. The levelling of areas to create building platforms will
also result in the displacement and exposure of subsoils. These impacts will have a negative visual
impact on the environment, which in some cases can be remediated. The project requires extensive
earthworks to meet the required horizontal and vertical alignments and curvatures for roads, so the
aesthetic impact is significant. Every stage of any construction project has a measurable impact on the
environment: the use of raw materials, transportation of materials from source to the building site,
the environmental footprint of the construction site, use of water, as well as waste removal and
disposal. Trees and other plants near the wires have to be maintained to keep them from touching
the wires. On some power line corridors, herbicides are used to control vegetation. When power lines
and their access roads are placed in undeveloped areas, they can disturb forests, wetlands, and other
natural areas. Emissions of greenhouse gases and other air pollutants, especially when a fuel is burned.
Use of water resources to produce steam, provide cooling, and serve other functions. Discharges of
pollution into water bodies, including thermal pollution (water that is hotter than the original
temperature of the water body).
RECOMMENDATIONS AND CONCLUSION
The project is moderately complex due to three alternatives and all have the same geotechnical
constraints as there are no changes in the geology. The geotechnical constraints can only be verified
and described in detail after the fieldwork phase, i.e. excavation of test pits etc. It is recommended
that a detail geotechnical investigation be conducted along the power line routes as well as substation
site in order to verify this desk study and to provide site specific appropriate founding solutions. The
recurrence interval of mining induced seismic events and potential undermining should be
determined and taken into consideration for the design of pylons and the substation.
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REFERENCES
Diop, S., Stapelberg, F., Tegegn K., Ngubelanga, S. & Heath, L. 2011. A review of problem soils in South
Africa. Council for Geoscience Report Number: 2011-0062.
Guidelines for Urban Engineering Geological Investigations 1995. Published by SAIEG & SAICE.
National Home Builders Registration Council (NHBRC). Home Building Manual, part 1 & 2, first
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