Application Research On The Influence Of Zhongliangshan Tunnel Excavation On Groundwater Environment

With the development of society,environmental damage has become an important issue affecting people ’s lives.Among them,tunnel excavation leads to a large amount of groundwater discharge,which has caused a series of disasters to become the focus of attention.Tunnel excavation in Southwest China generally leads to changes in surface water and groundwater environment.In water-rich tunnels,it may also cause the danger of water gushing and mud inrush,while karst water and underground river water cannot be blocked and can only be discharged.Excessive discharge of groundwater will lead to a large reduction in groundwater volume,a decline in water level,and even the drainage of groundwater and surface water within a certain depth.It may also cause a series of hydrogeological disasters such as river depletion and ground collapse,which have a serious impact on local production and life.Taking Huayan and Huafu tunnels in Zhongliang Mountain as examples,this paper uses Visual MODFLOW to simulate the groundwater seepage field after tunnel excavation,analyzes the changes of groundwater environment with time and under the influence of different rainfall,and fits the maximum drawdown point water level changes of Huayan and Huafu tunnels.The time model is established and the following conclusions are obtained :(1)The influence of geological and groundwater environment is relatively strong in the range of 1 km in some Zhongliangshan tunnel areas studied by field investigation.The number of karst collapses and well springs is obviously large,and the groundwater level decreases obviously.There is a certain influence within 2km of the tunnel area,there are fewer karst collapses and dry well springs,and the groundwater level also decreases.The main material and spatial conditions of karst collapse in the tunnel area are the thickness of the covering layer in the trough and valley position of the tunnel area,the good surface catchment conditions,and the more developed karst(especially in the shallow karst).The location of karst collapse has the following two characteristics.One is the collection area of surface water and groundwater.These areas are mainly the depressions and gullies in the valley,which are conducive to the formation of water confluence.The second is the area with strong groundwater flow cycle.(2)The total duration of groundwater environment restoration is affected by the total amount of drainage during tunnel construction.Huayan tunnel has a large amount of drainage,and it takes up to 18 years for the groundwater level to return to the initial state.Huafu tunnel has a small amount of drainage,and it takes up to 10 years for the groundwater level to return to the initial state.The longer the drainage time,the greater the total amount of drainage,the greater the influence range of groundwater,the longer the maximum drawdown of groundwater,and the longer it takes to return to the initial state.(3)When the average rainfall for many years is a constant value,and the groundwater level of the tunnel site is blocked at the same time as the tunnel is completed,the groundwater level begins to recover,and the initial groundwater level recovers quickly.The maximum recovery of the water level in the two years is about three-quarters of the maximum drawdown.(4)The time prediction of groundwater environmental impact can be divided into the following time periods from excavation and drainage to water plugging in Zhongliangshan area.Water level rapid decline period,water level rapid recovery period,water level slow recovery period and water level balance period.The damage of tunnel to groundwater will return to the state before tunnel excavation over time.(5)The recharge rate of rainfall to groundwater is different.The greater the rainfall,the shorter the influence time of tunnel excavation on groundwater.When the average annual rainfall is 1600 mm,the groundwater recovery time of Huayan and Huafu tunnels can be shortened by about 5 years compared with the average annual rainfall of800 mm.Huayan and Huafu tunnels and the new Zhongliangshan tunnel are both tunnels crossing Zhongliangshan.The actual monitoring data of groundwater in the new Zhongliangshan tunnel are in good agreement with the groundwater variation characteristics shown by the three-dimensional numerical simulation results of Huayan and Huafu tunnels.