Exploring the Effects of Initial Fabric Anisotropy due to Preshearing Stress History in Different Directions on the Undrained Behavior of Loose Sands

Abstract

The main objective of this study was to investigate the response of uniform sand under constant volume (i.e., undrained) conditions and how it is influenced by the initial anisotropy induced in the soil fabric due to preshearing stress history. The experimental program explored a range of parameters, including stress–strain response, tendency to volume change, phase transformation, flow instability, noncoaxiality between stress and strain rate, and the critical state line. To induce initial anisotropy, samples were presheared along different directions and subsequently tested using an Swedish Geotechnical Institute (SGI)-type bidirectional direct simple shear apparatus. The testing program focused on the effects of initial anisotropy that were induced by preshearing, resulting from the application of initial shear stress in various directions relative to the subsequent shearing direction. To interpret the variations of stresses within the samples, Budhu's approach for stress state determination in simple shear specimens was adopted. The results demonstrate that the stress–strain behavior and global volume change tendency of the soil are heavily influenced by the magnitude and direction of the preshearing stress history. Furthermore, the study reveals that the effects of stress history significantly diminish at large shear strains as the samples approach the critical state.