Experimental study on the mechanism of sand boils and associated settlements due to soil liquefaction in loose sand

Sand boils are a recognized phenomenon associated with soil liquefaction. However, the exact conditions required to produce sand boils remain unclear, and sand boil-induced settlement is difficult to quantify. The mechanism of sand boils and associated settlements due to soil liquefaction is investigated in this study using model testing. Loose saturated sand deposit is made in a transparent acrylic cylinder applied with torsional shaking to reproduce liquefaction and sand boils. An acrylic circular plate, whose diameter is slightly smaller than the cylinder's inner diameter, is placed on the model ground surface to mimic a non-liquefiable layer. The gap allows the liquefied sand to be ejected, leading to sand boils. The mechanism of sand boils and induced settlements is investigated by the transient variations of the measured water pressure at the sidewall, the recorded plate settlement, and the monitored video image. The influence of different thicknesses of the non-liquefiable layer, the gap sizes, and the overburden pressures on the sand boil-induced settlement is assessed quantitatively. It is found that the thicker the non-liquefied layer or the smaller ejecta gap size, the lower the amount of ejecta and associated subsidence is observed. The overburden pressure had relatively minor effect on the amount of ejecta, but it affected the amount of consolidation settlement significantly. Based on the obser-vation of test results, a theoretical ejection head is proposed to determine the condition leading to sand boils.