An experimental study of sand boiling in relation to shearing characteristics of liquefied soil

Ground settlements after liquefaction are usually evaluated based on the amount of soil contraction caused by shearing, the so-called negative dilatancy. It means that during and after an earthquake, a kind of consolidation occurs and a large percentage of the erupted material tends to be water. As such the soil particles erupted by sand boiling are usually ignored when estimating the amount of the settlement. In some special case, however, there is so much erupted soil that it cannot be ignored when evaluating ground settlement. This was the case in the liquefactions in Urayasu city during the 2011 Tohoku great earthquake and in Christchurch city during the 2011 Christchurch earthquake. In this paper, a series of shearing tests using a small shearing box were conducted to cause sand boiling using various shear strain histories and different kinds of materials. The results showed that in soils with low permeability, the amount of erupted soil is related to the critical shear strain, which is the strain required to for the recovery of the effective stress after liquefaction. It was also shown that the amount of ground settlement increases with increases in the critical strain.