DETERMINATION OF DEFORMABILITY AND TENSILE-STRENGTH OF ANISOTROPIC ROCK USING BRAZILIAN TESTS

This paper is the first of a series of two papers dealing with the det ermination of the deformability, tensile strength and fracturing of an isotropic 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 indir ect (Brazilian) tensile strength of transversely isotropic rocks, i.e. rocks with one dominant direction of planar anisotropy. A computer pr ogram based on the complex variable function method and the generalize d reduced gradient method was developed to determine the elastic const ants of idealized linearly elastic, homogeneous, transversely isotropi c 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 a nisotropic media from the failure loads measured during diametral load ing. Brazilian tests were conducted on four types of bedded sandstones assumed to be transversely isotopic. Based on strain measurements obt ained with 45 degrees strain gage rosettes glued at the center of the discs, the five independent elastic constants of the tested rocks coul d be determined. The elastic constants determined with the Brazilian t ests were compared with those obtained from conventional uniaxial comp ression tests. The indirect (Brazilian) tensile strength of the tested sandstones was found to depend on the angle between the apparent plan es of rock anisotropy and the direction of diametral loading. (C) 1998 Elsevier Science Ltd.