Influences of repeated liquefaction and pulse-like ground motion on the seismic response of liquefiable ground observed in shaking table tests

Abstract

Repeated liquefaction and pulse-like ground motion have drawn considerable research attention in geotechnical earthquake engineering in the last two decades. In this study, the influences of both phenomena on the seismic response of liquefiable ground were investigated based on the observed excess pore water pressure, acceleration, and displacement of a saturated sandy ground specimen during a series of 1-g shaking table tests, including sinusoidal and earthquake excitation tests. The results indicate that repeated liquefaction somewhat reduced the severity of liquefaction, and this was probably because of the densification of soil; however, this effect was negligible when the ground excitation was sufficiently strong. Soil degradation was identified during the excitation on the basis of the stress-strain relationship of soil obtained through one-dimensional shear beam idealization; moreover, further weakening of soil in addition to that caused by soil nonlinearity due to the buildup of excess pore water pressure was noticed. However, surprisingly, the soil stiffness during a replicated excitation generally decreased, and this was possibly due to the variation in the soil fabric after post-liquefaction deposition. The pulse-like ground motion induced larger peak values of soil shear strain because of the pulse-like shear strain oscillation and caused more rapid buildup of excess pore water pressure than those observed during a non-pulse excitation. Thus, the efficiency of pulse-like ground motions in triggering liquefaction was revealed.