Lateral resistance of a full-scale pile group in liquefied sand

Lateral load test was performed on a full-scale pile group following blast-induced liquefaction to evaluate pile-soil-pile interaction effects. The 3 X 3 pile group at 3.3 pile diameter spacing was driven into loose to medium dense sand. A single pile test was conducted for comparison. In contrast to preliquefaction tests, group interaction effects were insignificant after liquefaction. The lateral resistance of each pile in the group was similar and about the same as that for the single pile test. p-y curves were developed based on the bending moment versus depth data for R-u values of 95%. While the slope of p-y curves for nonliquefied sand typically decreases with continued deflection, the slope of the backcalculated p-y curves for liquefied sand increases with deflection. This phenomenon appears to be connected with load-induced dilation and a decrease in excess pore pressure locally around the pile. The p-y curves stiffened with depth and as the excess pore pressure ratio decreased. Equations were developed for p-y curves in liquefied sand which also account for the effect of variations in pile diameter.