Initial cyclic shear strain-based pore pressure generation model of saturated sands under cyclic stress loading

Abstract

The liquefaction and weakening of saturated sands under cyclic stress loading is a major concern in earthquake engineering. This study proposes a model based on initial cyclic shear strain (γ_c,i) to predict the excess pore pressure generation in undrained saturated sands. Here, γ_c,i is defined as the average cyclic shear strain prior to the significant accumulation of excess pore pressure. To calibrate and validate the model, a series of undrained stress-controlled cyclic triaxial (CTX) tests were conducted on Fujian sand with 10 % Kaolin clay (FS-10) and Silica sand no.7 with 5 % Kaolin clay (SS7-5). The FS-10 and SS7-5 specimens displayed typical flow liquefaction and cyclic mobility as they approached initial liquefaction. A critical excess pore pressure ratio (r_u,c) is introduced to characterize the effects of liquefaction failure modes on excess pore pressure generation. The model also incorporates reduction factors related to small-strain secant shear modulus and reference shear strain to account for variations in calculating γ_c,i. Ultimately, the initial cyclic shear strain-based model exhibited a strong correlation with experimental data under different confining pressures and loading cycles. In addition, it provides a critical initial cyclic shear strain for assessing soil liquefaction in engineering practices, particularly for improved ground with complex stress states.