Three-dimensional cracking and coalescence of two spatial-deflection joints in rock-like specimens under uniaxial compression

Abstract

Aiming at the fact that joints in rock mass exhibit different spatial extension directions, uniaxial compression tests of rock-like specimens were carried out to investigate three-dimensional cracking and coalescence of two spatial-deflection joints. Based on the 3D reconstructions of specimen CT images, 3D cracking behaviour and ligament fracture pattern were investigated. The fracture evolution of each fracture type was analysed. And the rock block instability and bearing capacity for a jointed coal pillar reflected by the experimental results is revealed. The results indicate that wrapping wing and anti-wing cracks are dominant inducement of ligament fracture, and the helical cracks tend to occur when the joint angle and spatial-deflection angle of specimens are relatively large. There were five fracture types of ligaments, two of which are complete crack coalescence, and the failure surface presents convex curve and twisted surface, respectively. The other three types are partial crack coalescence, the coalesced region may be the front and back region of ligaments, and the fracture surface presents trapezoid or inverted trapezoid. For specimens containing a pair of joints with no spatial deflection or small spatial deflection, when joint angle is less than 60°, the 3D rock fracture can be simplified into a 2D problem. With the increase of spatial-deflection angle, the ligament changes from crack coalescence completely to crack coalescence partially. The results also implied that when the joint is gentle and two sides of discontinuities cut the block with a trumpet shape, rock block instability is easy to occur.