Evolution law of water and mud inrush disaster in deep-buried tunnel crossing water-rich fault fracture zone

ObjectiveThe existence of water-rich fault fracture zones significantly influences the occurrence of water and mud inrush during tunnel construction. To study the disaster evolution mechanism during deep-buried tunnel excavation through water-rich fault fracture zones, Methodsthis study establishes a mechanical model of the impermeable rock mass based on the silo model and limit equilibrium theory, considering the width, length, and inclination angle of the fault fracture zone. The mechanical criterion for the minimum safe thickness of the impermeable rock mass is derived. Using MIDAS GTS NX numerical simulation, a three-dimensional fluid-solid coupling numerical model is developed to analyze the evolution pattern of displacement, stress, pore water pressure, and seepage velocity when tunneling into the fault fracture zone. ResultsThe results show that the minimum safe thickness of the impermeable rock mass is mainly influenced by the length, width, and inclination angle of the fault fracture zone, tunnel burial depth, and the mechanical properties of the impermeable rock mass. After tunnel excavation reaches the fault zone, internal displacement increases significantly, with abrupt changes in both the maximum and minimum principal stresses. The low pore water pressure zone expands considerably, showing a trend of initial slow decrease, followed by rapid decrease, and eventual stabilization. A high-velocity zone emerges within the fault, with overall model flow velocity increasing. During excavation, the maximum flow velocity at the tunnel face generally increases first and then decreases. ConclusionThis study provides important references for preventing water and mud inrush disasters in fault fracture zones.