Identifying the Change of Seepage Field in Karst Aquifer under Tunnel Engineering: Insight from FEFLOW Modeling

Water inrush is one of the most serious phenomena threatening the safety of tunnel construction. The West Qinling 1# tunnel, as the major section of the Bailong River diversion project, traverses a complicated karst area and would be faced with a water inrush disaster. Based on geological and hydrogeological conditions, the Finite element subsurface flow system software is used to simulate and predict the development of the natural seepage field and dredging construction conditions of the seepage field on the West Qinling 1# tunnel area. The prediction results show that the groundwater level will drop up to 113.9 m under dredging construction conditions, with an impact radius of up to 11.5 km. Seepage field evolution and water influx were simulated under two conditions of construction plugging construction, respectively. The prediction results show that the groundwater level in the middle part of tunnel 1# is 112.68 m depth without blocking condition with an influence range of 10.5 km. The maximum water volume per unit length of the karst cave increases to 4.32 m3/d·m. In the plugging condition, the influencing scope does not significantly reduce, but the extent of the impact is greatly weakened. The groundwater level generally dropped at 10–25 m depth and the karst cave section unit length of the maximum water volume of 0.83 m3/d·m in the rainy season. The achievements of this study would provide a vital reference for the prevention of water inrush in karst tunnel construction.