Effects of fines on monotonic undrained shear strength of sandy soils

Shear strength of liquefied sands is an important component in seismic slope stability evaluation. Experimental data on a host sand mixed with different amounts of fines content and a careful analysis of other available steady state strength (S-us) data show that fines content and relative density play important roles affecting S-us. Fines content is found to be the major factor affecting S-us. When the S-us data for sands are grouped into (a) relatively clean sands (<12% fines), (b) silty sands (12 to 32% fines), and (c) silts or sandy silts (>50% fines) at the same relative density, relatively clean sands show the highest S-us. Silts show the lowest S-us. Silty sands show intermediate strengths. Based on this data, lower-bound relationships are proposed for S-us as a function of D-r and fines content.