A cohesive fracture model for discrete element method based on polyhedral blocks

Failure processes are common in geomaterials under external loads. In this study, a cohesive fracture model (CFM) and its implementation in a graphical processing unit (GPU)-based discrete element method (DEM) solver is presented within the context of simulating the failure of rock and other geomaterials. The CFM and its GPU implementation advances the simulation of the processes of meso-fracture initiation, propagation, and interaction. The CFM discretizes a domain into a series of pre-defined rigid polyhedral blocks. These blocks are bonded along the contact faces by a cohesive criterion with normal and shear strengths. This poses a computational challenge as few DEM codes can simulate polyhedrons, and amongst those the limited number of particles and required computational run-time make it intractable to do simulations of more than a few thousand polyhedral elements. This makes it computationally infeasible to combine CFM with such DEM models for practical applications. However, the GPU based code Blaze-DEM does allow for simulations of tens of millions of polyhedrons within practical runtimes. In this study we implement the CFM in Blaze-DEM and show the efficiency and usefulness of the model using GPU compute. Two typical examples, including a block sliding along a slope and the fracture process of an arch structure, are used to verify the provided CFM. This is followed by the simulation of Brazilian tests and uniaxial tests of limestone using the CFM that are validated against laboratory experiments. These tests demonstrate that the provided CFM can simulate not only the fracture process well, but also mechanical behaviors at the meso and macro scale of the geomaterials. Furthermore, based on the failure mechanisms of the Brazilian test and uniaxial test, an inversion method is proposed to obtain the mechanical parameters in CFM.