Abstract:To investigate the stress relaxation and rupture mechanisms of mudstone under different degrees of unloading damage, numerical simulation of stress relaxation in unloading damaged mudstone was conducted. The influence patterns of mesoscopic parameters on macroscopic mechanical parameters were studied to determine the range of mesoscopic parameter values. The uniform design method suitable for multi-factor and multi-calculation analyses, combined with multiple regression analysis, was used to establish the quantitative relationships between macroscopic and mesoscopic parameters of mudstone samples based on the PFC2D parallel bond model, thereby calculating and determining the PFC2D mesoscopic parameters of mudstone. Using the obtained mesoscopic parameters, numerical simulations of stress relaxation in unloading damaged mudstone were conducted, and the results were validated against experimental results. The results showed that according to the evolution of mesoscopic energy, stress relaxation could be divided into three stages: low stress relaxation, high stress relaxation, and relaxation failure. Moreover, the first two stages were primarily characterized by the accumulation of mesoscopic strain energy, while the final stage was characterized by the release of mesoscopic dissipation energy. As the degree of unloading damage increased, the number of shear cracks significantly increased during stress relaxation, while the difference in the number of tensile cracks remained insignificant. The failure mode of mudstone during stress relaxation gradually transitioned from tension penetration failure to tension-shear composite penetration failure as the degree of unloading damage increased.
