Study Of The Design Of Dewatering In Underwater Tunnel Based On The Ground Water Environment Impact

The dewatering engineering of excavation for Shenglian island river-crossing tunnel may affect the function of groundwater resources, led to a decline in groundwater level, could lead to a down in regional natural environment and ecological environment. the change of the groundwater seepage field circulation system, caused the lake water level drop in island, caused residents drinking water supply difficulties and other issues.Combining with the engineering geological background and regional hydrogeological conditions, the preliminary design scheme of dewatering for river-crossing tunnel project is formed. The project will choose the way of dewatering:well pipe and well point drawdown. And according to the principle of its design, I carry on the preliminary dewatering scheme design. According to the different geological situation, this paper will be divided into three sections of the tunnel across the river section design. Considering the lake in Shenglian island and the project of tube well precipitation influence each other, and tunnel island export section (LAKO+800～LAKO+1060) influence radius calculation value is658m, and the radius of influence is bigger on the island and the lake, and it had a greater influence on the groundwater, I use the target function method:The minimum sum of the project cost and the minimizing environmental economic loss is objective function; The water level drawdown of foundation pit, and the water yield size of single well are constraint conditions; Finally we can get the least precipitation well, minimum water output of precipitation scheme optimization in the tunnel section. This paper use the groundwater numerical simulation software to forecast the optimal dewatering well layout, analyses the tunnel surrounding the possibility of surface subsidence and the impact of regional groundwater resources, and proposes corresponding groundwater environmental protection measures.Through the forecast of water level drawdown by MODFLOW, this paper show us that: the project dewatering radius of influence is consistent to the radius of influence on Sargent diving formula, so the project precipitation scheme is feasible. For the exit section of tunnel, the drop of underground water level along the direction of tunnel is slow, and on both sides of the tunnel water level drop is bigger, the scheme of optimizing skillfully avoid the tunnel section of the influence to the lake water level. And make the most of reducing the impact on the surrounding groundwater environmental during the period of well point dewatering tunnel, reducing the water level trend change. So the project engineering precipitation in the study of optimization scheme is feasible.