Discrete element modelling of water diffusion and softening characteristics in rocks

Abstract

The water softening effect is a critical factor that can cause or exacerbate large deformation phenomena or even instability in rock engineering. In this study, a meso water diffusion and softening model is proposed based on the discrete element method, the theory of saturated-unsaturated seepage and damage theory, which can be used to characterize the moisture diffusion process between rock pores quantitatively, as well as the mechanical behaviour of rock particles undergoing parameter deterioration subjected to a water-induced softening effect. In addition, by comparing the simulated values with the results of mercury intrusion, water absorption and uniaxial compression tests, the rationality of the proposed model has been validated. Furthermore, the relationships between the saturation coefficients and the mechanical parameters of rock samples are researched, and the moisture distribution characteristics of rock samples and their impacts on the meso mechanical parameters under water absorption, evaporation and closed boundary conditions are studied, as well as the evolution of the number of microcracks in rock samples during uniaxial compression tests. The research results indicate that the strength and stiffness parameters of the particle elements exhibit non-linear degradation with increasing saturation coefficient. With the same saturation coefficient, the degradation degree of the uniaxial compressive strength and elastic modulus of the sample during the evaporation process is usually greater than that of the sample during the saturation process. Compared with that in the low-saturation samples, the number of cracks in the high-saturation samples significantly increased under water absorption conditions. In contrast, the number of cracks in the sample does not change significantly with decreasing saturation under evaporation conditions. The proposed model provides a new approach for studying the water-softening effect in rocks using the discrete element method.