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Definition of an engineering soil Soil is an uncemented (or weakly cemented) accumulation of mineral particles formed by the weathering of rocks, the void space between the particles, containing water and/or air. 1 Figure 1.1. The rock cycle 2 Scale Figure 1.6. Single grain structure 3 Figure 1.1. Clay (kaolin). 4 1 Silica sheet Gibbsite sheet Silica-gibbsite sheet 5 Figure 1.1. The rock cycle kaolinite illite 6 montmorillonite Water molecule Figure 1.8. Clay minerals. 7 8 2 Specific surface: Surface area per unit mass Sand Small Specific surface Coarse sand 0.002m2/g 1mm diameter Fine sand 0.02m2/g 0.1mm diameter Silt 0.2m2/g 0.01mm diameter Dispersed Flocculated Natural soil Figure 1.9. Clay structure Sieve analysis Clay Large Specific surface Kaolinite 10 - 20m2/g Illite 65 - 100m2/g 0.1m thick Montmorillonite up to 800m2/g 0.01m thick 9 11 1m thick 10 Hydrometer 12 3 Non-plastic Plastic 13 Plastic limit test Liquid limit test Casagrande apparatus 14 Fall cone apparatus 15 16 4 Figure 1.12. Plasticity chart 17 Figure 1.1. The rock cycle 18 Description of soil Jennings, Brink and Williams (1973) M - Moisture C - Colour C - Consistency S - Structure S - Soil type O - Origin 19 20 5 Description of soil Description of soil Structure Cemented / bonded Fissured (closed joints) Jointed Bedding planes Intact (no joints of fissures) Slickensided Moisture Dry Slightly moist Moist Very moist Wet Soil type Clay / silt / sand / gravel Consistency Coarse material Fine material Very loose Very soft Loose Soft Medium dense Firm Dense Stiff Very dense Very stiff Origin Geological origin 21 Figure 1.15. Phase diagrams 22 23 6