A zero-thickness cohesive element-based numerical manifold method for rock mechanical behavior with micro-Voronoi grains

In this study, a zero-thickness cohesive element-based Numerical Manifold Method (NMM) combined with detailed micro-scale characterization is proposed for modeling the rock mechanical response and failure process of rock. To represent the rock micro-structure, a Voronoi tessellation technique is adopted to generate the random polygonal grains. Since the contact fracture model not only requires input micro-parameters which are difficult to be obtained directly from laboratory tests, but also becomes very time consuming due to extensive contact searching and judging processes, a zero-thickness cohesive element is inserted between the rock grains to more efficiently and accurately capture the interaction between the rock grains before failure. To more efficiently model the interaction between the rock grains after failure, the original contact searching technique is improved. To validate and illustrate the efficiency of the developed method, a series of numerical tests are performed using the developed method and their results are compared with those obtained from laboratory tests and original NMM predictions. Since the NMM adopts an implicit scheme to solve the problem, a large time step is allowed, which makes it possible to realistically model the static loading condition without need of raising up the loading rate required by other explicit-based methods.