Determination of deformability and tensile strength of anisotropic rock using Brazilian tests

Abstract

This paper is the first of a series of two papers dealing with the determination of the deformability, tensile strength and fracturing of anisotropic rocks by diametral compression (Brazilian test) of discs of rock. It presents a combination of analytical and experimental methods for determining in the laboratory the elastic constants and the indirect (Brazilian) tensile strength of transversely isotropic rocks, i.e. rocks with one dominant direction of planar anisotropy. A computer program based on the complex variable function method and the generalized reduced gradient method was developed to determine the elastic constants of idealized linearly elastic, homogeneous, transversely isotropic media from the strains measured at the center of discs subjected to diametral loading. The complex variable function method was also used to construct charts for determining the indirect tensile strength of anisotropic media from the failure loads measured during diametral loading. Brazilian tests were conducted on four types of bedded sandstones assumed to be transversely isotropic. Based on strain measurements obtained with 45° strain gage rosettes glued at the center of the discs, the five independent elastic constants of the tested rocks could be determined. The elastic constants determined with the Brazilian tests were compared with those obtained from conventional uniaxial compression tests. The indirect (Brazilian) tensile strength of the tested sandstones was found to depend on the angle between the apparent planes of rock anisotropy and the direction of diametral loading.