Grain-based distinct element modeling of thermally induced slip of critically stressed rock fracture

Abstract

The present study introduces a numerical approach to simulate thermally induced fracture slip using a grain-based distinct element model. As part of DECOVALEX-2023 Task G, we verified the model through benchmarks, explored the thermo-mechanical processes under various conditions, and validated the model against laboratory experiments on both saw-cut and tensile-splitting fractures. In this method, the rock sample was represented by a group of polyhedral grains, such as random Voronoi diagrams or tetrahedra. The thermo-mechanical behavior of the grains and their interfaces was calculated using the distinct element method. Additionally, a novel method to determine micro-parameters of grains and contacts based on an equivalent continuum approach was proposed. The main emphasis was placed on simulating the temperature evolution, thermal stress development and fracture displacements under thermo-mechanical loading. The benchmarks demonstrated the model’s ability to replicate fracture behavior under various conditions, in good agreement with analytical solutions, capturing the phenomena of fracture slip and opening. In the modeling of laboratory experiments, a comparison between the experimental results and the numerical results revealed that the model reasonably reproduced the heat transfer within the rock specimen, the horizontal stress increment depending on boundary condition, and the progressive fracture shear failure. Although discrepancies existed regarding the onset of fracture slip and the magnitudes of stress and displacement, the model demonstrated qualitative consistency with the experimental findings. By tracking the contact area variation, we also found that the model effectively mimicked the mechanism of asperities shear-off, irreversible damage and normal dilation that occur during the peak stage.