Development of a three-dimensional grain-based combined finite-discrete element method to model the failure process of fine-grained sandstones

This paper introduces a novel three-dimensional grain-based hybrid finite-discrete element method parallelized based on general-purpose graphic processing units (GPGPUs) and applies it to investigate the failure process of sedimentary fine-grained sandstones. The grain-based method considers the actual microstructures of rocks with Voronoi or grain-growth tessellations to model their failures, including transgranular, intergranular and intra-granular crack propagations. The novel semi-adaptive contact activation approach (semi-ACAA) proposed by the authors and the efficient tetrahedron-to-point (TtoP) contact interaction algorithm developed by HOSS are implemented to speed up grain-based modelling in addition to GPGPU parallelization. Semi-ACAA and TtoP are approximately 2-20 times and 1.5 times faster than the brute-force contact activation approach and tetrahedron -to-triangle contact interaction algorithm, respectively, which are prevalent in the FDEM community. The grain -based modelling elucidates that most intragranular cracks are observed in the medium-and high-strength grains of the sandstones, while most intergranular cracks occur at the grain boundaries between low-and high-strength grains. The transgranular cracks do not discriminate any grains on their propagating paths but propagate and coalesce with intragranular and intergranular cracks, which results in the final failure of the sandstones.