DEM Modeling of Interaction Between the Propagating Fracture and Multiple Pre-existing Cemented Discontinuities in Shale

It is known that pre-existing discontinuities can act as planes of weakness that divert the propagating fractures in rocks, but previous studies have mostly focused on the interaction between the propagating fractures and a single pre-existing discontinuity. The influences of multiple pre-existing cemented discontinuities, such as calcite veins and bedding planes, on the fracture propagation still remain poorly understood. In this study, particle-based discrete element method was used to characterize the fracturing behavior of shale containing multiple cemented veins and bedding planes through numerical semi-circular bend (SCB) tests. Model results show that geometrical and mechanical properties of multiple pre-existing cemented discontinuities can significantly affect the interaction modes between the induced tensile fractures and pre-existing cemented discontinuities, as well as the mode I fracture toughness of shale. The typical mechanical interaction modes between the induced tensile fractures and the multiple pre-existing cemented discontinuities and the corresponding conditions are given. The effect of pre-coexisting discontinuities on the peak loads for shale during SCB tests is also discussed.