Response of liquefiable sloping site to mainshock-aftershock ground motions

Abstract

Aftershocks following a major earthquake can induce substantial cumulative damage in liquefiable soils, thereby posing considerable risks to critical infrastructure systems. To explore the re-liquefaction behavior and site deformation patterns of sloping sites under the combined effects of the mainshock and aftershocks, liquefiable sloping site models are established using PDMY and PIMY constitutive models to simulate the nonlinear behavior of sandy and clayey soils. Soil responses to mainshock-aftershock ground motion sequences with varying intensity ratios are analyzed and compared in terms of excess pore pressure ratio (EPPR), acceleration, residual displacement, and shear stress-strain hysteresis. The results indicate that mainshock-aftershock ground motions cause more severe liquefaction in the sand deposit than the mainshock alone, leading to greater lateral spreading of the soil. The aftershock-mainshock intensity ratio governs the degree of liquefaction and soil lateral spreading; it increases the degree of liquefaction in non-liquefied soils, while previously liquefied soils re-liquefy after initial liquefaction. However, it has a slight influence on the rise in pore water pressure. As the aftershock-mainshock intensity ratio increases from 0.5 to 2.0, the maximum attenuation of the acceleration peak in liquefied soil reaches 325.53 % and the horizontal displacement increases by 278.72 %. Similarly, the settlement at the slope crest and the uplift at the slope toe are amplified to 5.07 and 5.18 times the values from the mainshock, respectively. The shear strain of the soil demonstrates clear shear slip characteristics, indicating that the aftershock significantly enhances the shear response of liquefied soil, which further promotes the development and accumulation of deformation.