Effect of Fines on Sand Residual Strength after Liquefaction

The shear force on a metal coupon dragged through liquefied sand was measured in a modified triaxial apparatus. This device allowed much larger strains and strain rates to be imposed than in a conventional triaxial liquefaction test. The effect of varying fines content on the post-liquefaction large-strain residual shear resistance was measured for specimens prepared at a range of different densities, and compared with residual strength values back-calculated from field liquefaction slope failures. Increasing fines content was found to decrease the residual strength compared to that of clean sand under similar placement conditions. Values measured in the laboratory under truly undrained conditions were comparable to lower-bound values obtained from field cases, suggesting that the laboratory values represent a conservative lower bound for fully-undrained conditions during sliding.