Bidirectional Shear Wave Velocity Measurements to Track Fabric Anisotropy Evolution of a Crushed Silica Sand during Shearing

Abstract

Continuous bidirectional shear wave velocity measurements were performed in the vertical ($V$ ) and horizontal ($H$ ) directions to characterize fabric evolution of triaxial soil specimens during shear, wherein, in addition to the vertical direction, two specially designed horizontal bender elements’ housings were mounted on samples using a new measurement technique. The specimens were prepared using moist tamping and water sedimentation methods and then subjected to strain-controlled triaxial compression shear under drained condition. Different sets of stress paths were applied to uncover the evolution of fabric during consolidation and shearing. The magnitudes of the shear wave velocities in different directions highlighted severe soil anisotropy at the critical state. It was found that the shear wave velocities were governed by void ratio, effective stress, and sand fabric. Interpretation of results shows the limited accuracy of the conventional empirical functions to predict the initial shear modulus in the consolidation stage. A fabric function taking into consideration the role of the soil fabric on soil elastic moduli was proposed, and its variations were traced during shear. Variations of the fabric function underline that there exists a unique anisotropic fabric at the critical state.