Simulating Groundwater Inflow in the Underground Tunnel with a Coupled Fracture-Matrix Model

Groundwater inflow during tunnel excavation is a common problem in practice. How to accurately predict its occurrence during the construction is still a challenging problem for tunnel designers. A numerical method, based on the coupled model involved in artery fractures described by a discrete fractured network model and ramification fractures and rock matrix described by the equivalent continuum medium model, is developed to calculate the groundwater inflow of underground tunnel. The model is calibrated with the observed groundwater levels in the study domain. The results in the model calibration show that calculated and measured groundwater inflows agree well. Sensitivity analysis indicates that groundwater inflow increases with the increase of precipitation rate, hydraulic conductivity of rock matrix and fracture aperture. The effect of fracture aperture on groundwater inflow is predominant, owing to the occurring of many artery fractures around the tunnel, which leads to much groundwater flowing to the tunnel through these fractures.