Experimental study on the reliquefaction behavior of saturated sand deposits under distinct loading frequencies

In this study, the liquefaction and reliquefaction behaviors of saturated sand deposits were investigated through two parallel 1-g shaking table tests, focusing specifically on the effects of loading frequency. It was observed that the sand exhibited a dilative tendency under lower-frequency excitations and liquefied in the mode of cyclic mobility, signaled by evident dilation spikes and acceleration amplifications. In contrast, under higher loading frequencies, the soil showed a contractive behavior characterized by acceleration attenuation and cyclic instability. A five-stage liquefaction model was proposed to describe the evolution of soil behavior throughout the entire liquefaction process. The investigation of the test results, which was based on the staged model, suggested that higher-frequency loading induced more extensive liquefaction across deeper zones but required more shear cycles to reach initial liquefaction. Analysis of the strain-stress response indicated that lower loading frequencies resulted in higher developed strain and increased soil stiffness. It was found that the distinct soil behaviors can be attributed to the compound effects of input motions in terms of both loading amplitudes and drainage conditions. However, despite the different field responses, trends in the evolution of liquefaction stages across different depths and shaking events were observed to be consistent under the varied loading frequencies. Additionally, the change in liquefaction resistance under multiple shakings was also in accordance for both tests, in which the resistance in the liquefied areas significantly reduced during the second shaking event but recovered in subsequent events, whereas the resistance in the unliquefied areas increased monotonically with each event. Regarding the ground settlement, the settlement rate remained relatively higher when the excess pore pressure ratio was maintained at 1.0, and the total settlement in each event continued to decrease as the field gradually densified.