Anisotropy and directionality of tensile behaviours of a jointed rock mass subjected to numerical Brazilian tests

Strong anisotropy of tensile behaviros and spatial anisotropic deformation have been found in transversely isotropic rock discs. There is seldom attention paid for the insightful analysis of anisotropy and spatial variability of tensile behaviours for jointed rock masses. In the paper, an index termed as the "directionality" was proposed to quantitatively assess both the directionality and spatial variability of tensile strength of jointed rock masses. Experimental Brazilian tensile tests were carried out on stratified biotite granulite rocks. Corresponding to the configurations of laboratory tests, numerical simulations of rock specimens with different joint distributions and discrete fractures network (DFN) models were then performed using PFC2D code. The results indicated that the stratified rock discs displayed distinct anisotropy and directionality in tensile strength, manifested by the decreasing strength with inclination angle. The maximum directionality of the stratified rocks measured in laboratory was 2.40/0 degrees, which was perpendicular to the layered discontinuities, while the tensile strength determined by DFN models showed a lower anisotropy and directionality (1.38/30 degrees). Obvious anisotropic characteristics were observed in the fracture patterns of failure in DFN models. This paper implies the necessity of consideimg the anisotropy and directionality for the study of failure mechanisms of surrounding rocks in underground tunnels.