A Comparative Study on Leakage Magnitude Occurred in Reservoir While Passing a Tunnel Beneath Reservoir

To prevent a decrease in the water level of the reservoir caused by water surges and seepage from the tunnel beneath the reservoir, it is essential to clarify the hydraulic connection between the reservoir and the underpass tunnel. A MODFLOW three-dimensional grid model was developed using GMS 10.6 software to examine this hydraulic connection. The model focused on the section of the tunnel beneath the reservoir, investigating the effects of factors such as the permeability coefficient of the stratum, rainfall recharge, fault permeability, aquifer thickness, and the silt layer at the reservoir’s bottom on tunnel water inflow. Additionally, the relationship between tunnel water inflow and reservoir water levels was analyzed. The results indicate that the presence of faults enhances the hydraulic connection between the tunnel and the reservoir. An increase in fault permeability leads to greater water inflow into the tunnel at the fault location. As the permeability coefficient of the stratum increases, the decline in reservoir water levels follows an S-shaped curve. The silt layer at the bottom of the reservoir helps mitigate the drop in water levels caused by tunnel water inflow. When the water influx is below 0.4 m3/d, the reservoir water level remains unaffected. However, when the influx exceeds 0.7 m3/d, the water level decreases rapidly as the influx increases. At an influx near 1 m3/d, the reservoir level drops by approximately 7 m. The reservoir is particularly susceptible to leakage when the fault penetrates the bottom of the reservoir and forms a hydraulic connection with the tunnel. This study provides a predictive method for assessing reservoir water level reductions caused by tunnel surges, which can aid in mitigating such effects in the future.