Effect of fabric on shear wave velocity in granular soils

Abstract

The small-strain elastic shear wave velocity (V_S) is a basic mechanical property of soils and is an important parameter in geotechnical engineering. Recently, V_S has been adopted as one of the indices for development of liquefaction charts. This implies that if a parameter affects V_S, it may also affect liquefaction resistance. Some of the parameters whose effects have been accounted for include relative density, stress state and geologic age. An important parameter that affects both liquefaction resistance and VS is fabric. Quantification of in situ fabric is still an open problem and hence, considerable judgement is needed in order to map laboratory test results to field conditions. In this paper, we conduct numerical simulations at the grain-scale to investigate the effect of fabric on V_S. We start by showing that two granular assemblies, with the same stress state and void ratio but different fabrics, can exhibit different trends in liquefaction behavior. Furthermore, via a numerical implementation of the bender element test, we obtain two distinct trends of V_S anisotropy for the two granular assemblies. Finally, we consider three different fabric measures based on contact properties and explore correlations between V_S anisotropy and fabric anisotropy. We also look at fabric tensors of the ‘strong’ and ‘weak’ network, respectively, of the granular assemblies. Our results suggest that for liquefiable soils, i.e., recent Holocene-age deposits with negligible cementation and with a stress history of seismic loading, a knowledge of V_S anisotropy can give information about fabric anisotropy. A knowledge of in situ fabric could help in more accurately mapping laboratory test results to field conditions.