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90 CORRELATIONS OF SOIL PROPERTIES <br />TYPICAL ANGLES OF EFFECTIVE SHEARING RESISTANCE FOR COMPACTED CLAYS - <br />Soil description Class" (deg) <br />Silty clays, sand-silt "x SM 34 <br />Clayey sands, sand?la SC 31 <br />Silts and clayey silts ML 32 <br />Clays of low plasticity CL 28 <br />Clayey silts, elastic silts MH 25 <br />Clays of high plasticity C 19 <br />•UniGed classification system. <br />plasticity index increases and she s ngttidecreases. As described <br />previously, the strength of clay n effec 've stress terms, is basically <br />frictional so c'= 0. This is cert my the case th remoulded saturated <br />clays but partially saturat clays, where me 'sous effects draw the <br />particles together to pr uce inter-particle sty s, may appear to <br />have a small cokes' n value, though this ite is a frictional <br />phenomenon. <br />Typical values the angle of shearing resistance, q5', fo ompacted <br />clays are give to Table 6.3. Values are for soils compact to the <br />maximum d density according to the standard compactio tes <br />(AAS•HT0 9,5.51b rammer method, or BS 1377:1975 test 12, 2. <br />yammer ethod). <br />6.4 SHEAR STRENGTH OF GRANULAR SOILS <br />Because of their high permeability, pore water pressures do not build <br />up when granular soils are subjected to shearing forces, as they do <br />with clays. The complication of total and effective stresses is therefore <br />avoided and the phenomenon of apparent cohesion, or undrained <br />shear'strength, does not occur. Consequently, the shear strength of <br />granular soils is defined exclusively in terms of the frictional resistance <br />between the grains, as measured by the angle of shearing resistance.. <br />Typical values of the angle of shearing resistance for sands and <br />gravels are given in Table 6.4. <br />Typical values for compacted soils are given in Table 6.5. Values <br />refer to soil compacted to maximum dry density at optimum moisture <br />content as defined in the standard compaction test: AASHTO T99 <br />(5.5lb rammer method) or BS 1377:1975 test 12 (2.5kg rammer <br />method). <br />A relationship between dry density or relative density and the angle <br />of shearing resistance is given by the US Navy (1982), as shown in <br />R e,(-a e-/-f <br />SHEAR STRENGTH 91 <br />Table 6A TYPICAL VALUES OF THE ANGLE OF SHEARING RESISTANCE OF COHESIONLESS <br />SOILS <br /> ¢ (deg) <br />Material <br /> Loose Dense <br />Uniform sand, round grains. 27 34 <br />Well-graded sand, angular grains 33 45 <br />Sandy gravels 35 So <br />Silty sand 27-33 30-34 <br />Inorganic silt 27-30 30-35 <br />Table 6.5 TYPICAL VALUES OF THE ANGLE OF SHEARING RESISTANCE FOR COMPACTED <br />SANDS AND GRAVELS <br />Soil description Class* Angle of shearing <br /> resistance, 0 (deg) <br />Well-graded sand-gravel mixtures GW >38 <br />Poorly-graded sand gravel mixtures GP >37 <br />Silty gravels, poorly graded sand-gravel-silt GM >34 <br />Clayey gravels, poorly graded sand-gravel-clay GC >31 <br />Well-graded clean sand, gravelly sands SW 38 <br />Poorly-graded clean sands, gravelly sands SP 37 <br />Unified ela{strieation system. <br /> 50 <br /> c <br /> 0 <br /> <br /> <br />y 40 <br /> C O <br />- m a+ <br />• <br />-fLl ? O <br />V <br /> 'A 30 <br /> 0 <br /> m <br /> a 20 <br />Dry denalty - t/In3(Mq/me) <br />,Rgure 6.13 Typical values of density and angle ofshearing resistance of cohesionless <br />soils (modifted after US Navy, 1982) <br />-? 1.4 1.5 i.a 2.o 2.2 2.4