Cyclic liquefaction of granular materials with varied forms under multidirectional loads

Both the liquefaction resistance of granular materials under complex multidirectional cyclic loadings and the influence of particle form or morphology on that resistance are poorly understood. This paper presents an experimental investigation on this topic. Round, frosted, concave and convex glass beads as well as Hong Kong completely decomposed granite (CDG) sand were used to prepare samples with varying particle morphologies (i.e. roughness, sphericity, aspect ratio and convexity). Unidirectional and multidirectional cyclic simple shear tests were performed to examine the liquefaction susceptibility and highlight the specific role of various particle morphologies. Results show that the increase of shape irregularity and surface roughness both result in a considerable liquefaction resistance improvement. Moreover, overall shape has a more fundamental effect on liquefaction behaviour than surface roughness. An enhanced morphology index, providing a collective description for the particle geometry and surface texture, are proposed to optimise the correlation with liquefaction behaviour. In addition, it is discovered that multidirectional loading could exacerbate the generation of pore pressure and trigger a sharp increase in shear strain amplitude at a lower excess pore pressure ratio. Accordingly, a novel analytical procedure for estimating the liquefaction resistance, independent of cyclic loading patterns and particle morphology, is developed and validated by additional data in the literature.