Plastic-strain-dependent strength model to simulate the cracking process of brittle rocks with an existing non-persistent joint

Brittle rock failure has been extensively studied for decades and is recognized as a process of crack initiation, propagation, and coalescence. However, the cracking mechanism is still not fully understood. Numerical approaches are generally used to study the cracking process of rocks with pre-existing joints. The strength model of the rock matrix is crucial and should be adopted appropriately in numerical studies. This paper presents a plastic-strain-dependent strength model of brittle rocks based on a series of cyclic loading-unloading compression tests and Brazilian tension tests in the laboratory. The detailed steps used to obtain the mechanical parameters quantitatively during progressive failure are presented. It is shown experimentally that both the shear strength parameters and tensile strength vary during the failure process, i.e., cohesion weakening, frictional strength mobilization, and tensile strength loss (CWFS-TL). The model is then implemented in Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) to represent the properties of the rock matrix, and the interface element in the software is adopted to simulate the non-persistent joint. Two types of numerical experiments are conducted on specimens with a pre-existing non-persistent joint: a direct tension experiment on a specimen with a horizontal joint and a uniaxial compression experiment on a specimen with an inclined joint. It is found that the cracking process in the numerical experiments can capture nearly all the features of physical experiments under the same conditions in the laboratory, and the numerical results also agree quantitatively with the theoretical solution. It seems that the approach can be widely used to study brittle rock masses with a non-persistent joint.