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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