Experimental study on dynamic response law and failure mode of ice-rock composite slope under strong earthquake via shaking table test

【Objective】Ice-rock composite slopes are prone to trigger high-position, high-speed and long-runout ice-rock avalanche disaster chains under strong earthquakes, which constitutes one of the key challenges for seismic geohazard prevention in the southeastern margin of the Qinghai-Tibet Plateau. 【Methods】Taking the ice-rock composite slope at Zelongnong vally, Milin County, Linzhi City, Xizang as the geological prototype, a three-layer physical model consisting of bedrock, glacier and moraine layers is fabricated following similarity theory. Shaking table tests are performed to systematically investigate the evolution of dynamic characteristics and acceleration amplification effect of the ice-rock composite slope under strong seismic excitations, and the failure mode is analyzed by PIV measurement technique. 【Results】The results show that: (1) The initial natural vibration frequency of the moraine layer is 31.68 Hz. With the gradual increase of seismic amplitude, its natural frequency decreases continuously by a total of 62.1%, and the damage evolution presents a distinct two-stage pattern: initial damage stage and damage failure stage. (2) The PGA amplification factors of moraine and bedrock layers increase first and then decrease with rising excitation frequency, peaking near 21 Hz due to resonance. By contrast, the PGA amplification factor of the glacier layer declines monotonically with frequency and responds remarkably under low-frequency excitation. (3) A typical elevation amplification effect exists along the vertical direction of the slope. As input acceleration rises, the PGA amplification factor of the moraine layer rises first then falls, while that of the glacier layer keeps increasing; the maximum difference in dynamic acceleration response between the two layers occurs at 0.7 g. At identical excitation amplitude, PGA amplification factors under sine wave loading are notably larger than those under Wenchuan seismic wave. (4) The slope fails in a shear-tensile cracking-sliding mode. The failure evolution proceeds as initiation of superficial shear cracks in the moraine layer - crack propagation and coalescence to form sliding surface - sliding along the formed surface - overall instability. No obvious failure occurs in the glacier and bedrock layers throughout the test. 【Conclusion】This study reveals the progressive instability mechanism dominated by the moraine layer for ice-rock composite slopes under seismic loading, which can provide references for risk prevention of ice-rock avalanche hazards and major engineering construction in southeast Tibet.