Segmented-bond based discontinuous deformation analysis method and its application in sandstone rupture

In deep coal mining, the combinations of high temperature, high ground pressure, high karst water pressure and stress disturbance lead to a discontinuous deformation and complex rupture behavior of the surrounding rocks. Reproduction of the rock failure process using the numerical approaches becomes an important way to study the rock rupture phenomena and to reveal associated failure mechanisms. With a strict mathematical foundation in contact representation, numerical integration, and convergence examination, the improved DDA method with block subdivision strategy and bond representations can effectively simulate the failure process of fractured rock masses from continuous elastic deformation stage to progressive failure stage, and the complete breakage stage. Based on the idea of piecewise characterization of the edge-edge bonding effect, a segmented edge-edge bond model is proposed, where the linear and nonlinear bonding constitutive relationships are equivalently characterized by paired penalty springs at the center of each segment. The segmented edge-edge bond models are embedded into the conventional framework of the discontinuous deformation analysis with a triangular segmentation for the optimized simulation of rock fracturing process. By the deformation and stress analysis of the simulation results in the center compression test of the simple support beam, the uniaxial compression and the Brazilian splitting test of rock specimen, the accuracy of the proposed model is verified. The reasonable values or ranges of the segmentation number, bonding stiffness ratio, tangential-to-normal stiffness ratio and other associated parameters of the segmented edge-edge bond are obtained. In the numerical simulation of uniaxial compression test for complete and cavitated sandstone specimens, the assignment methods of the deformation associated parameters (e.g., block elastic modulus, block Poisson ratio) and the strength associated parameters (e.g., bond tensile strength, bond cohesion, and bond friction angle) are clarified. Also, the accuracy of the proposed model in reproducing the stress-strain curve and initial cracking position is verified. In the numerical investigation of the Brazilian splitting test of sandstone with single or combined flaws, the feasibility of the proposed model in reproducing crack initiation, propagation and intersection is verified. In summary, the proposed segmented edge-edge bond model can be applied for investigating the failure phenomena and mechanisms of rock masses with complex fracture networks.