Mesoscopic mechanism of increasing liquefaction resistance of saturated sand deposits by preshaking using centrifuge shaking table tests

Geological hazard surveys demonstrate that the history of prior seismic events could affect soil liquefaction resistance under the subsequent earthquakes. The liquefaction of soil with prior seismic history seems not sensitive to the densification after prior reconsolidation. Many attempts of the previous studies have concentrated on the mechanism, impacts, and evaluation of prior destructive seismic history, including large cyclic shear strain and liquefaction history. However, less attention has been paid to the mesoscopic mechanism of the nonliquefying histories commonly caused by weak earthquakes from an experimental view. In this study, centrifuge shaking table tests combined with an inflight mesoscopic image acquisition system were utilized to investigate the macroscopic and mesoscopic behaviors of clean sand deposits under complex seismic sequences. The sequence consisted of three types of seismic motion with different intensities that were equivalent to weak, medium, and strong earthquakes, respectively. Experimental results show multiple weak earthquakes can improve sand liquefaction resistance obviously, which was demonstrated by different evolution patterns of reliquefaction resistance during the tests with and without prior weak earthquakes. The beneficial effects of nonliquefying history were also seen in the cases of models with extensive liquefaction history. Mesoscopic images analysis revealed that multiple weak earthquakes eliminated slender voids, made the particles that constituted loose mesostructures rotate to equalize the voids distribution, and caused quick downward movement of small particles to strengthen interlocking effects among particles.