University of Pretoria GEOLOGICAL PROCESSES AND MATERIALS SGM210 22 April 2014 1 GEOLOGICAL MAPS 1. Dip 2. Strike 3. Faults 2 1
2
FAULTS 3 San Andreas Fault 3
14 18" 26" JJJ' 22 4 (.) 5I cr w o(aigcegroup, tic.) 65 DKelahal1Group Urtenhage ond Zulullllld Gtoopt Dml<6nlbergend lebombo M*no,Eliot end a..-fomebonl Karoo SIMPLIFIED GEOLOGY OF SOUTH AFRICA LESOTHO AND SWAZILAND llofswana t,. 0?' Uḻ 0 crn ze Q. 250 I Cepe lleuor1gtajp Dwpca end EoceGtoupe Sope<vroup, Notal Group Cape GraniteSuite, etc. 5<15 DVnnrhyntdolp end NarneG!ouJ.e NA 11BlA D Alkaline cortlliox" 2050 l!ultmiid c:ornpex (folllc) '> /'!.!.. t- N JfJ" \ 0 80 160 240 320km 34' l'o'iipiulir\ ' U:Ysta (dp"tkicj)ft ('1X,'0ltt*CHO 'I('f 1e -------- ------ ------------ ---------------- 22' ----------- FORMASIE FORMATION SEOIMENTE " RE KOLOM/SEOIMENTARY COLUMN (IHStUITEIIDE VUOO!i!ESE GESTEENTES/IIIClUDDIG vot.cawic IHOS) UTOLOGIEI LITHOLOGY Silverton Daspoort Skalie, plek-plek koolstofhoudend; horingfels, chert Shale, carbonaceous in places; hornfels, chert Kwartsiet Quartzite Ysi VAALIUM VAALIAN SWAIIUM SWAZIAN Subgroep Malmani{ Malmani Subgroup Strubenkop Skalie plek-plek vsterhoudend Shale in places ferruginous Kwartsiet, chert, jaspihet Dwaalheuwel Quartzite, chert, iaspilile Hekpoort Vulkaniese oesteentes Volcanic rocks Boshoek Kwartsiet Quartzite. Skalie, sliksteen, plek-plek konglomeraat ; kwartsiet ( Timeball Htll Shale, siltstone, conglomerate in places: quartzite ( Duitschland Penoe Konglomeraat Conglomerate Ysterryke skalie Iron-rich shale Oolomiet ; chert ( Dolomite; chert ( ) ) Kwartsiet. konglomeraat, skalie; kwartsiet ( );dolomitiese Black Reef kalksteen ensblie(: : :-:); onsuiwer kwartsiet en konglomeraat ( ).. Quartzite, conglomerate, shale: quartzite ( ); dolomitic limestone and shale (:-:-:-:); impure quartzite and conglomerate ( ) Bloempoort Blou en geel gestreepte leiklip, kwartsiet Blue and yellow banded slate, quartzite Dennilton Granof1riese oneis: skis engranuliet ( :m: ) Granophyric gneiss; schist and granulite ( ;:;:;:;: ) Granietgneis plek-plek graniet ; gneis enamhboliet (" :) Granite-gneiss, granite in places; Qneiss and amphibolite (". : ) ) ) * 4
SGM210: INTRODUCTION TO GEOTECHNICAL ENGINEERING 1. Basic geology of South Africa 2. Description of soils and rock 3. Problem soils of South Africa 4. Geotechnical structures (practical applications) 6 SOIL A three-phase material Grain Grain Air Grain Grain Grain Grain Three phases 1. Solids 2. Water 3. Air 7 5
SOIL A three-phase material Phase 1 1. Solids material not continuous like steel, concrete or wood, material small discrete particles, only positive stresses possible, no tension unless cemented, particles assumed to be incompressible. 8 SOIL A three-phase material 9 Stress in soil 6
SOIL A three-phase material 10 Stress in soil SOIL A three-phase material d α T h c Phase 2 2. Water voids in soil saturated or unsaturated, pressure in water >0 kpa or <0 kpa, can push grains apart or pull them together, ease with which water flows through soil = permeability (measured in m/s), water assumed to be incompressible. 11 4 cos 4 cos 1 7
Stress in soil partially saturated soils cling Gravity is a myth earth sucks! 12 SOIL A three-phase material Phase 3 3. Air in unsaturated soils, compressible, air pressure usually disregarded. 13 8
SOIL A three-phase material Grain Grain Air Grain Grain Grain Grain Solids+Water+Air=SOIL A tricky material... It even has a memory!!! 14 Soil types, according to particle size Gravel Sand Silt Clay 9
Particle size Gravel >2mm Sand 0.06 2mm Silt Clay 0.002 0.06mm < 0.002mm Gravel 600mm 10
Sand Silt 11
Clay Clay 5μm 12
Sand vs Clay Cohesionless vs plastic Sieve analysis to measure particle size distribution 13
Sieve analysis Hydrometer test 14
Soil classification according to particle size 200mm 60 2 0,06 0,002mm Particle size range 60mm 2mm 60μm 2μm 15
Particle size range Cobble Clay Plate 1μm 10mm 100mm 1km 1km = Soccer City Complex Presenting particle size range % passing 100 90 80 70 60 50 40 30 20 10 0 0.001 0.01 0.1 1 Particle size (mm) 10 S1a S2 S3 S4a S5 16
Soil classification according to particle size 20 10 0 100 90 80 Example: Classification of mixture comprising 40% sand, 20% silt, 40% clay = Sandy clay 30 Clay 70 40 60 50 50 60 Sandy clay Silty clay 40 80 70 Clayey sand Clayey silt 30 20 90 Silty sand Sandy slit 10 Sand Silt 100 0 10 20 30 40 50 60 70 80 90 0 100 %Silt Soil mechanics: The scientific study of = saturated soil 17
Soil: The influence of moisture No volume change possible Shrinkage limit Plastic limit w S w P Volume change possible Liquid limit w L Dry soil SOLID SEMI SOLID PLASTIC LIQUID DRY Increasing moisture content WET Attributes of Water Content & Limits Identified as part of field profile description (MCCSSO) Simple & inexpensive to test in the field or lab Important parameter in soil classification systems Important parameter in mobilising shrink/heave of soils 18
The water content limits Dr A. Atterberg: Prof. Arthur Casagrande: 1911 1932 Atterberg Limits Liquid Limit Swell Limit w L w SW (approx 2/3 of I P ) Plastic Limit w P Shrinkage Limit w S Linear Shrinkage L S Indexes of the Atterberg Limits Plasticity Index (PI) I P =w L -w P Dry soil SOLID SEMI SOLID PLASTIC LIQUID Increasing moisture content The influence of moisture Symbol for moisture content = w Shrinkage limit w S Plastic limit w P Liquid limit w L Dry soil SOLID SEMI SOLID PLASTIC LIQUID Increasing moisture content 19
The significance of Atterberg limits Suspension Phase Water Content: w >>> w L Saturation: 100% Water Pressure: + Behaviour:liquid Dry soil SOLID SEMI SOLID PLASTIC LIQUID Increasing moisture content Slurry Phase Water Content: w>w L Saturation: 100% Water Pressure: + Behaviour:thick liquid Dry soil SOLID SEMI SOLID PLASTIC LIQUID Increasing moisture content 20
Merriespruit tailings dam failure 22/2/1994 Plastic Phase Water Content: Saturation: Water Pressure: Behaviour:Plastic w P <w<w L 100% from + to Dry soil SOLID SEMI SOLID PLASTIC LIQUID Increasing moisture content 21
Measuring liquid limit Casagrande apparatus Measuring plastic limit 3mm 22
Semi Solid Phase Water Content: w S <w< w P Saturation: ~100% Water Pressure: Negative Behaviour:Elasto-Plastic Dry soil SOLID SEMI SOLID PLASTIC LIQUID Increasing moisture content Solid Phase Water Content: Saturation: Water Pressure: Behaviour:Brittle w < w S 0% to 100% Strongly Negative Dry soil SOLID SEMI SOLID PLASTIC LIQUID Increasing moisture content 23
Water content & shrink/swell Development = changes water content Disrupt evapo-transpiration cycle -> increase moisture Removal of plants & shrubs -> increase moisture Planting of trees & shrubs -> decrease moisture Other causes of moisture changes Leaking services Excessive irrigation Seepage & moisture flow barriers IMPORTANT SOIL PROPERTIES STRENGTH (when does it fail?) STIFFNESS (how easily does it deform?) PERMEABILITY (how easily does water pass through it?) 24