Experimental investigation of compressional wave effects on soil liquefaction resistance

Abstract

This study addresses a critical gap in liquefaction analysis by investigating the effect of vertical motion (P-waves), which is often neglected but significant in near-fault regions. A series of advanced cyclic triaxial tests was performed to simulate liquefaction behavior under vertical wave propagation (P-wave), where the confining pressure was cyclically changed in addition to the cyclic axial loads used to simulate shear (S) waves. The test program included isotropically and anisotropically consolidated specimens subjected to P-wave, S-wave, and in-phase P + S-wave loading. The soil response under different loading conditions is then discussed and compared, revealing insightful similarities and differences from the typically observed cyclic soil behavior subjected to S-wave. The test results show that P-wave-induced porewater pressure oscillation is instantly offset by increased confining pressure, maintaining constant effective stress under isotropic conditions; thus, liquefaction evaluation must use effective stress rather than excess porewater pressure that could exceed the initial effective confining stress as soil is subjected to P-wave. Under anisotropic conditions, by contrast, very high P-wave loading could lead to soil liquefaction due to the cyclic deviatoric stress they induce. Nevertheless, the soil liquefaction resistance under P + S-wave loading is similar to that under S-wave loading alone, indicating that the current design practice of considering only S-waves may be valid.