Wave velocities and their relation to fabric evolution during the shearing of sands

The fabric of a sand strongly dominates its stress–strain behavior during monotonic and cyclic shearing. In this study, two pairs of piezoelectric ceramic transducers built into a triaxial cell, which are capable of measuring the compressive and shear wave velocities propagating in the axial direction, were developed. A series of triaxial tests using different stress paths were conducted on sand to investigate their mechanical properties and to simultaneously measure the compressive and shear wave velocities. The measured wave velocities varied, depending on stress path and stress state. A new measure, referred to as the fabric index, was derived using elastic theory for a cross-anisotropic material in association with a micromechanics-based stress–strain model. This index was used to evaluate fabric evolution along various stress paths in three types of sand. The effects of confining pressure, current stress ratio, stress path, and stress history on the fabric index are discussed in detail.