Limit Drainage of Separated Tunnel Based on Ecological Groundwater Table: A Case Study

After the excavation of the tunnel in water-rich regions, the groundwater is continuously discharged into the tunnel. Excessive discharge will cause the groundwater table to drop, which will destroy the normal growth of vegetation and ecological balance. In order to protect the ecological environment, the key is to develop an effective method to determine the tunnel drainage. In this paper, a method for calculating the limit drainage of the tunnel is proposed based on area-well method and the concept of ecological groundwater table in ecology and agronomy. Some conclusions are drawn as follows. (1) When the ecological groundwater table is constant, with the increase of groundwater discharge, the drainage influence range of the tunnel decreases, the rainfall supplement quantity W t within the drainage influence range decreases, and the total groundwater discharge quantity Qt also decreases gradually. Since the decreasing rate of W t is greater than that of Qt, there is a unit drainage that makes the total groundwater discharge equal to rainfall supplement. (2) A separated tunnel under construction in Fuzhou City is taken as an example; the limit drainage q0 of the separated double tunnel is 0.48 m3/(m·d) considering ecological groundwater table.