Undrained behaviour of two silica sands and practical implications for modelling SSI in liquefiable soils.

The aim of the present study is twofold. Firstly, the paper investigates the undrained cyclic and post-cyclic behaviour of two silica sands by means of multi-stage cyclic triaxial tests. Secondly, based on the post-cyclic response observed in the element test, the authors formulate a simplified stress–strain relationship that can be conveniently used for the construction of p–y curves for liquefiable soils. The multi-stage loading condition consists of an initial cyclic loading applied to cause liquefaction, followed by undrained monotonic loading that aimed to investigate the post-cyclic response of the liquefied sample. It was found that due to the tendency of the liquefied soil to dilate upon undrained shearing, the post-liquefaction strain–stress response was characterised by a distinct strain–hardening behaviour. The latter is idealized by means of a bi-linear stress–strain model, which can be conveniently formulated in terms of three parameters, i.e.: (i) take-off shear strain, γto, i.e. shear strain required to mobilize 1 kPa of shear strength; (b) initial secant shear modulus, G1, defined as 1/γto; (c) post-liquefied shear modulus at large strain, G2 (γ⪢γto). Based on the experimental results, it is concluded that these parameters are strongly influenced by the initial relative density of the sample, whereby γto decreases with increasing relative density. Differently both shear moduli (G1 and G2) increases with increasing relative density. Lastly, the construction of new p–y curves for liquefiable soils based on the idealized bi-linear model is described.