Numerical characterization of groundwater flow and fracture-induced water inrush in tunnels

Abstract Recently, the rapid increase in tunnel construction in karst areas across China has attracted considerable attention. However, frequently occurring groundwater inrush hazards induced by fractures within rocks are one of the greatest challenges faced during tunnel excavations. In this paper, we present a numerical investigation on the effect of fractures on fluid flow, considering the different types of discontinuities. A conceptual model of fracture-induced water inrush, which emphasizes the evolution of fracture connectivity, was developed to investigate the fluid flow through fractured rocks and consequently study the water inrush mechanism. The numerical results indicate that the rock fracture serves as the preferential flow channel and the aquifuge acts as a barrier to the groundwater flow. Groundwater is transported mainly through fractures with higher permeability. A case study demonstrated the accuracy of the proposed conceptual model. Finally, the influences of the connected fractures on water inflow and the sensitivity of the different types of connected fractures to tunnel inflow were investigated using the orthogonal experiment method. The proposed approach and results may contribute to the investigation of groundwater movement in fracture system, thereby providing a basis for the water-inrush theory and prevention of damage in karst areas.