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 (ΔS), cyclic normal (ΔN) stress increments, the ratio ΔS/ΔN, and the phase shift (δ) 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 [Formula: see text] and subjected to coupled cyclic loading with representative ΔS/ΔN. For a given cyclic stress ratio (CSR) and initial [Formula: see text], the liquefaction resistance decreases with increasing s-wave intensity relative to p-wave intensity, which are proxies to stress increments ΔS and ΔN, respectively. Liquefaction resistance decreases with an increase in ΔS/ΔN up to a limiting value of about 2 beyond which increasing ΔS/ΔN does not significantly influence the cyclic resistance. The finding that cyclic resistance ratio [Formula: see text] decreases with increasing ΔS/ΔN 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 Kσ factor (ratio of cyclic resistance at [Formula: see text] to resistance at [Formula: see text] = 100 kPa) can be considered even under generalized coupled loading conditions.