Hydro-mechanical coupled behavior analysis of multi-jointed rock mass under triaxial compression based on the discrete element method

Accurate assessment of jointed rock mass hydro-mechanical behavior prevents engineering geohazards caused by water pressure. This study conducts triaxial compression tests on jointed rock samples under varying water pressures using the discrete element method (DEM). A full-coupled hydro-mechanical (HM) model links mechanical and hydraulic fields, with joint fluid flow following the cubic law. On the basis of material parameter calibration against laboratory test data, the study explores the hydro-mechanical coupling behavior of blocky and stochastically jointed rock. An innovative approach integrates ultrasonic pulse velocity (UPV) testing with triaxial compression tests to create stochastically jointed rock models aligned with the Geological Strength Index (GSI) chart. This UPV-based calibration method enables representation of stochastically jointed rock models as blocky/disturbed rock masses within the GSI chart. Simulations identify rotation and detachment failure modes in rock blocks under high water pressure and low confining pressure. Results show that the generalized Hoek-Brown (H-B) criterion, expressed in terms of effective stress, is unsuitable for rock masses with few joints, particularly under high water pressure. The effective stress principle applies only to highly blocky or less interlocked rock mass structures in the GSI chart. The study highlights joint connectivity’s significant influence on the effective stress coefficient.