Impact of initial dry density on the evolution mechanism of mud and water burst in fault fracture zones: A series of experimental studies

Mud and water bursts within fault fracture zone frequently lead to casualties, equipment damage, and project delays, posing significant risks. A thorough scientific understanding of these mechanisms is essential for effective disaster prevention and control. To investigate the evolution mechanisms of mud and water burst in fault fracture zones, an experimental apparatus was designed to simulate the migration and loss of filling material particles under triaxial loading conditions. Experiments conducted with this apparatus explored the evolution process of mud and water bursts under varying initial dry densities. The results demonstrate that the evolution of mud and water bursts is a complex process, characterized by increased porosity and permeability, decreased strength, and fluctuating viscosity. The initial dry density plays a critical role in determining the failure mode of mud and water bursts. At low initial dry densities, the filling material is prone to seepage failure. In contrast, at high initial dry densities and elevated water pressures, the material is more likely to experience splitting failure. In comparison to seepage failure, the evolution process of splitting failure exhibits a significant delay, with a longer incubation period. However, it can rapidly form seepage channels in a short time, leading to more severe mud and water bursts. Finally, the study analyzed variations in porosity, permeability, and shear strength associated with different failure modes. Generalized models were established to describe the evolutionary characteristics of both seepage and splitting failure. These findings offer valuable insights for improving the safety and stability of tunnel engineering in environments prone to such risks.