Comparison of the post-liquefaction behaviour of hard-grained and crushable pumice sands

While the factors affecting the liquefaction resistance of sands have been studied by many researchers, their behaviour post liquefaction needs further examination. More specifically, understanding the effects of various parameters on the stress-strain relation of sands during the post-liquefaction stage is important not only for the purpose of assessing the magnitude of ground deformations induced by liquefaction, but also in investigating the impact of these deformations on buried structures, such as pipelines and pile foundations. In this paper, the post-liquefaction stress-strain behaviour of both hard-grained (silica) and crushable (pumice) sands is examined and attempts are made to express the stress-strain relation using a bilinear model which can be defined in terms of three parameters: initial shear modulus (G1), shear modulus at recovery (G2), and dilation shear strain (dil) when the soil starts to dilate during post-liquefaction state. For hard-grained sands, it is observed that the three parameters are dependent on the initial relative density (Dr), i.e. with the increase in Dr, G1 and G2 would increase while dil would decrease. On the other hand, test results on pumiceous sand show that, regardless of Dr, the value of G1is larger while that of G2 and dil are smaller compared to those of a hard-grained sand. This can be attributed, partly at least, to crushing of the particles and their high angularity which induce interlocking between them when monotonically sheared.