Abstract
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.
Highlights
With the development of economy and the improvement of transportation facilities in various regions, the construction of large-scale tunnels is increasing year by year, which brings new opportunities to the development of transportation and economic growth, and brings challenges to the local ecological, hydrological, and geological environment [1,2,3,4,5,6,7,8,9]
After the tunnel construction in Seoul, the annual discharge of groundwater was 63 million m3, and the groundwater table decreased from 16.85 m in 1996 to 20.40 m in 2003 [12]. e construction of a railway tunnel through the Hallandsas ridge in the southwest of Sweden resulted in drying up private wells and springs close to the tunnel axis due to groundwater drawdown [6]. e construction of Zhongliangshan tunnel in Chongqing caused 29 ground surface collapses and dried up 48 springs [13]. e influence area of surface water was about 7.2 km2, which seriously endangered the living and production water of local residents [14]
According to the proposed groundwater seepage model, the influence range of groundwater drainage funnel is derived under the premise of controlling the maximum groundwater drawdown within the range required by normal growth of vegetation. en the rainfall supplement quantity Wt within the influence range is obtained by using the method of rainfall infiltration coefficient, and Wt is compared to the total groundwater discharge quantity Qt. rough adjusting groundwater discharge q0 to make Wt equal to Qt, q0 is the maximum allowable groundwater discharge in the tunnel site
Summary
With the development of economy and the improvement of transportation facilities in various regions, the construction of large-scale tunnels is increasing year by year, which brings new opportunities to the development of transportation and economic growth, and brings challenges to the local ecological, hydrological, and geological environment [1,2,3,4,5,6,7,8,9]. During tunnel excavation and operation in water-rich regions, groundwater leaks through the tunnel, so the groundwater table drops [8, 10, 11] as shown, leading to the reduction of surface water storage and even springs drying up. The decrease of surface water and groundwater caused the shortage of water supply in the local ecosystem, which lead to the deterioration of plant growth. Tunnels excavation decreased the soil water contents and changed plants water uptake patterns in karst areas [17]. Such adverse effects of tunnel drainage occurred, because the waterproofing-drainage measures in the past for tunnels
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