Characterization of transverse anisotropy in Poisson's ratio using three-point radial deformation measurements

¹ Middle East Technical University, Department of Civil Engineering, 06800 Ankara, Turkey
² Yapı Merkezi, 34676 Istanbul, Turkey

^* Corresponding author: toker@metu.edu.tr

Abstract

Poisson's ratio (v) of rock specimens can be experimentally determined from radial deformation measurements in an unconfined compression test. This is commonly achieved by mounting a compressometer with diametric or perimetric measurement capability, both of which assume the specimen cross-section remains a circle. If there is anisotropy among the horizontal directions, this assumption fails and measurements err. In this study, a compressometer with three radial deformation measurements is developed. The accuracy of new compressometer in determining the mean of the two v values along the two axes of anisotropy is theoretically investigated, assuming the deformed specimen is an ellipse in cross-section. Then, to capture separate v values along the axes of anisotropy, data from actual tests employing the new device were analysed in two different approaches: Assuming the centroid of the cross-section remains stationary (1) does not produce physically reasonable results. Assuming the specimen moves laterally and v values are constant (2) is possible through a grid search-type optimization algorithm. This results in calculation of the orientation of axes of anisotropy with respect to the compressometer, as well as the corresponding v value.