Optimization Of Tudiya Tunnel Dewatering And Analysis Of Its Impact On Ground Water Environment

The dewatering engineering of excavation for Tudiya tunnel may affect the function of groundwater resources, leading to a decline in groundwater level, which will have a negative impact on regional natural environment and ecological environment and bring plenty of problems to residents' drinking water supply and irrigation water supply. Also, during construction of tunnel, tunnel inflow happens easily, threatening the safety of tunnel construction, especially when groundwater is acid, eroding reinforcing bar of tunnel. In order to solve these problems, I have done the following work:1. There is an extensive survey on geological background and regional hydrogeological conditions of Tudiya tunnel construction area.2. The dewatering engineering of excavation for Tudiya tunnel is pre-designed. 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 divide the Tudiya tunnel into three sections. I take regional groundwater sensitive points, such as farmland, vegetation and wells as evenly distribution so as to simplify the minimization of environmental damage caused by precipitation into minimization of pumping amount of single-well. With objective function method, the dewatering program design of three sections of tunnel is optimized:the objective function is the minimum of the maximum one of the single-well pumping quantity in the three tunnel sections; constrains are total desired pumping quantity of these three sections and dewatering program budget; the solutions of the model are minimum single-well pumping quantity. The optimization results show that it is necessary to build 6, 20 and 4 wells in three sections respectively and their construction costs are as follows: 104,000 yuan,955,000 yuan and 36,000 yuan. Since the middle section of the tunnel with high depth and high pumping quantity, the cost of dewatering in the middle section of the tunnel is much higher than the cost of others.3. With Visual MODFLOW program, groundwater seepage field after the optimal dewatering program is forecast. Through comparison of groundwater level before and after construction, groundwater drawdown level of each section is calculated. The results show that, requirements of groundwater drawdown level of each section are met after the dewatering program and groundwater levels have dropped below the level on which the tunnel will be constructed, namely the dewatering program is feasible. Radius of influence in phreatic aquifer is calculated by formula and it shows that the dewatering program has large radius of influence. The middle section of the tunnel, the pumping quantity of which is the largest, has a 2000m radius of influence, leading to some impact on the environment and surrounding residents.4. Thus, this paper presents some corresponding protection methods to reduce the impact of tunnel construction on the surrounding groundwater environment. In order to alleviate the potential risk, a comprehensive monitoring and emergence program is proposed.