Stress redistribution and crack evolution during fault slip: Insights from coupled finite-discrete element method simulations

Fault zones containing fluids such as water, gas, or oil exhibit reduced mechanical stability, making them more prone to reactivation and slip. Understanding how stress redistributes during slip is essential for assessing fault-related risks in fluid-bearing formations. This study employs the coupled finite-discrete element method to simulate fault activation and stick-slip behavior, validated against laboratory experiments. The numerical model effectively captures stress variations on fault planes, stress field distribution in surrounding rock masses, and local stress and fracture evolution within the fault zone. By analyzing key engineering parameters such as confining pressure, fault thickness, friction coefficient, cohesion, and surrounding rock strength, the study assesses their impact on fault mechanics. The simulation results reveal that fault slip induces stress redistribution, primarily characterized by the rotation of the principal stress direction near the fault and the heterogeneity of stress distribution. Thinner faults exhibit more pronounced tip effects, leading to higher stress gradients. Increasing fault cohesion suppresses crack formation and enhances fault stability. In contrast, lower friction coefficients promote particle displacement, concentrate stress, and result in localized slip. The crack evolution analysis demonstrates a transition from shear-dominated damage during the early loading stage to tensile crack dominance during fault activation. This study provides valuable insights into the stress field of the fault and surrounding rock mass during fault reactivation. The developed numerical model offers a robust tool for simulating complex fault behaviors, contributing to improved practices in geotechnical engineering and seismic risk assessment.