Mechanical characterisation of jointed rock-like material with non-persistent rough joints subjected to uniaxial compression

Understanding the mechanical behaviour of jointed rock particularly under uniaxial compression is so important for an appropriate design of structures on or within a rock mass. Jointed rocks may consist of persistent or non-persistent joints. Typically, the persistent joints can dominate the whole mechanical behaviour of jointed rocks while the effects of non-persistent joints on the rock masses require careful consideration during the characterisation process. Majority of the earlier studies on the non-persistent jointed rocks have included the joints with open smooth surfaces while the behaviour of jointed rocks with non-persistent rough joints has been explored very limitedly. Therefore, in this study, a number of artificial jointed rocks with non-persistent rough joints were tested under uniaxial compression. With the aid of 3D printing technology a wide range of joint roughness has been accommodated inside the artificial samples. The joints were parallel or coplanar. The influences of four different parameters including Joint Roughness Coefficient, bridge length, bridge angle and joint angle on the uniaxial compressive strength, the deformation modulus and the crack coalescence stress of jointed rocks were investigated through multivariate statistical analysis using Response Surface Methodology. In total, 30 experiments were conducted and the resulting failure patterns were classified into six different categories based on their crack coalescence conditions. A number of samples revealed a specific failure pattern known as “fish eye” due to the development of “asperity interlocking cracks” which were associated with the high range of joint roughness. From Response Surface Methodology it was found that all the four parameters had individual and interactive effects on the uniaxial compressive strength and the deformation modulus of jointed rock. Also, it was concluded that the overall mechanical behaviour of a jointed rock with non-persistent rough joints is mainly controlled by the joint angle under uniaxial compression.