Experimental study of the effects of initial shear stress on post-liquefaction behavior of submarine liquefiable ground: An energy-based evaluation

In offshore earthquake regions, granular soils are prone to liquefaction and flow failure, resulting in imponderable damage to adjacent structures. When the foundation is constructed on inclined terrains, initial static shear stress induced by the self-weight of slope soils can significantly affect the soil behavior and liquefaction potential. This paper discusses the effects of initial shear stress on the liquefaction and post-liquefaction behavior through an energy-based approach. A series of monotonic and cyclic undrained simple shear tests are performed under various initial shear stress levels. The cumulative dissipated energy is used to evaluate the effects of initial shear stress on typical soil behaviors, including the onset of instability in monotonic tests and the liquefaction in cyclic tests. In monotonic tests, the cumulative energy required for triggering instability decreases with the initial shear stress level at the post-liquefaction stage. Moreover, at the same relative density, a strain-softening response on virgin samples can be transformed into a strain-hardening type at the post-liquefaction stage. In cyclic tests, a unique correlation is found between cumulative energy and pore water pressure and it is closely related to the initial shear stress level. Based on the test results, two relationships are proposed to estimate the cumulative energy required for liquefaction or flow-type failure at the initial liquefaction and post-liquefaction stages.