Laboratory measurements of stress-induced velocity anisotropy in unconsolidated sands

Abstract

An experimental device for measuring the transverse isotropic (TI) elastic properties of sediments under uniaxial strain conditions has been developed. The phased array compaction cell utilizes matched sets of P- and S-wave ultrasonic transducers located along the sides of the sample and an ultrasonic P-wave phased array source with pinducer receiver on the ends of the sample. The phased array provides plane P-waves that are used to measure phase velocities over a range of angles. From these measurements, the five elastic constants for TI media can be recovered as the sediment is compacted, without the need for sample unloading or reorienting. Descriptions of the apparatus and data processing and an application to an unconsolidated sand sample are provided in this paper. P-wave anisotropy of 20% has been observed in dry sand under an axial stress of 5 MPa.