Time-dependent deformation and failure of granite based on the virtual crack incorporated numerical manifold method

Abstract Micro-cracks are known to greatly affect the mechanical properties of granite and subcritical crack growth (SCG) is considered to be the main mechanism of brittle creep in rocks, including granite. Here, we provide new uniaxial compressive strength and creep experiments for Lanhelin granite, and a new multi-crack numerical model to explain the experimental observations. We first thermally-stressed our granite samples to create thermal micro-cracks. Uniaxial compressive strength experiments were then used to find the uniaxial compression strength of the thermally-cracked granite, a pre-requisite for brittle creep experiments. We introduced a new model that combines SCG theory and the numerical manifold method (NMM) to link the local damage caused by micro-crack propagation and the macroscopic creep deformation observed in the granite samples. We also investigated the influence of virtual micro-crack length, confining pressure, and differential stress on brittle creep behavior. According to our model, we can numerically simulate the entire creep process, from the small deformation caused by micro-cracks to the large displacement characteristic of brittle creep. The fact that the numerical simulations are in good agreement with experimental results shows that the NMM combined with the SCG theory is a suitable method for modeling the creep behavior of rocks.