This research proposes a novel Grain-Based Model (GBM) for the simulation of transversely isotropic rocks. The model introduces Rigid Body Spring Network bonds and a fictitious stress approach into the Discrete Element Method in order to generate the anisotropic elastic behavior and utilizes breakable particles to manifest cleavage failure. The new model is verified by comparing numerical stress bulbs from a point load analysis against a finite element solution and by comparing unconfined compression strength test results from Asan Gneiss GBM against Jaeger's ‘plane of weakness’ theory. Of note, the novel grain-based model allowed the direct determination of macroscale anisotropy in elastic and strength properties without the need for trial-and-error calibrations of input parameters. In addition, the proposed breakable grain scheme provided for realistic representations of the failure modes usually observed in rocks with cleavage.
The majority of numerical research that applied the Discrete Element Method to the analysis of transversely isotropic rocks used the Bonded Particle Model (BPM) technique (Potyondy & Cundall 2004), with Smooth Joints (Ivars et al. 2008) generating the numerical representation of cleavage planes and anisotropy in deformability and strength (e.g., Park & Min 2015 and Zhao et al. 2022). Alternatively, the Grain-Based Model (GBM) or Bonded Block Model (BBM) technique has also been used (Lan et al. 2010), with tetrahedral particles replacing spherical ones. In GBM, anisotropy was introduced by means of particles elongated in the direction of isotropy plane (Ghazvinian et al. 2014) or using geometry that conformed to the cleavage planes orientation (Huang et al. 2022).
Both BPM and GBM/BBM techniques have attracted the attention of researchers in rock mechanics due to their ability in investigating realistic failure phenomena while grounded on simple theories and assumptions. On the other hand, trial-and-error calibration is necessary to define the model's input parameters that can provide a match with properties observed in laboratory.
The objective of this study is to propose and investigate two contributions to enhance the GBM/BBM technique for the simulation of transversely isotropic rocks: the adoption of Rigid Body Spring Network bonds combined with a fictitious stress method for generating the anisotropy in elastic behavior; and a novel breakable grain scheme for the manifestation of cleavage fracture without the need for preconditioned meshes or Smooth Joints.
