Effects of coupled seepage and seismic histories on liquefaction resistance of shallow sand deposits

Seismic histories induced by minor earthquakes could improve the sand liquefaction resistance, whereas those induced by strong earthquakes could decrease the sand liquefaction resistance. The action of upward pore fluid seepage on shallow sand deposits during the post-liquefaction process was determined to be one of the mechanisms of these natural phenomena. Based on this background, a series of 1g shaking table tests were carried out to analyze the effects of pore fluid seepage on the sand reliquefaction resistance in subsequent earthquakes. Experimental results showed that the decreasing effects of the seepage history on the sand liquefaction resistance were limited by the input seismic intensities and applied hydraulic gradient (i). Weaker or more extensive seismic motions (cyclic stress ratio, CSR<0.32 or >0.67, respectively) and i values less than 0.5 would not noticeably decrease liquefaction resistance. In the case of inputting successive motions with a medium CSR and i=3.0, the liquefaction resistance of the sand deposits with seepage histories decreased in the first two shakes in comparison with the deposit models without seepage histories. A longer seepage duration correlated to a much lower liquefaction resistance. These results demonstrated that the interaction of the soil layers during reconsolidation should be considered in evaluating the liquefaction risk of the ground.