Liquefaction of sands subjected to principal stress rotation caused by generalized seismic loading

Abstract

A comprehensive experimental study that quantifies the influence of coupled compression and shear wave loading on liquefaction susceptibility of sands is presented. Such loading is typical in situ, and leads to complex principal stress rotation, which in turn impacts the potential for liquefaction in soils even if the cyclic loading intensity remains constant. The nature and degree of principal stress rotation caused by this coupled loading are significantly influenced by the initial consolidation stress state, and the cyclic shear (DS), cyclic normal (DN) stress increments, the ratio DS/DN, andthephase shift (d ) between the waves. Cyclic hollow cylinder torsional shear tests were carried out on Fraser River sand specimens isotropically consolidated to different effective mean normal stress s0mc and subjected to coupled cyclic loading with representative DS/DN. For a given cyclic stress ratio (CSR) and initial s0mc, the liquefaction resistance decreases with increasing s-wave intensity relative to p-wave intensity, which are proxies to stress increments DS and DN, respectively. Liquefaction resistance decreases with an increase in DS/DN up to a limiting value of about 2 beyond which increasing DS/DN does not significantly influence the cyclic resistance. The finding that cyclic resistance ratio CRR decreases with increasing DS/DN is consistent with the understanding that the cyclic resistance is lower under simple shear loading mode compared to triaxial shear. Tests results also demonstrate that the liquefaction resistance of sand decreases with increasing initial effective confining stress regardless of the nature of the cyclic shear. This indicates that the correction Ks factor (ratio of cyclic resistance at s0mcto resistance at s 0mc = 100 kPa) can be considered even under generalized coupled loading conditions.