Analysis On The Effect Of The Groundwater Environment Of Taiyuan Metro Line No.2 Project

In recent years, in order to alleviate the contradiction between supply and demand of urban traffic, pull the framework of this big city, support the development of the city to the south, Taiyuan first planned for the seven rail transit lines and Metro Line 2 is the first line. Taiyuan Metro Line 2 is the main skeleton line of Taiyuan rail transit network, from north to south across the city of Taiyuan. After the completion it can not only alleviate the pressure of the main traffic, promote and guide regional development along the construction, but also can drive the city to expand to both north and south directions, guide the urban population and urban functions to evacuate to the new district of the city, drive the development of urban economy.However, the construction of urban rail transit will inevitably affect this fragile groundwater environment. This paper takes the Taiyuan City Metro Line 2 project as the research object, the geological and hydrogeological data of the study area as the foundation, analyzes the influence on groundwater environment respectively from the construction and operation period two stages: Identifying hydrogeological characteristics of the study area, the recharge, runoff and discharge conditions of the groundwater before deepen analysis the hydro-geological situation of the project area; defining the precipitation scope of the construction zone, the area and the way of influence;predicting water inflow of each station in construction section and accordingly analyzing the ground subsidence which may induce; analyzing the relationship between the trend of the subway tunnel and the groundwater runoff; calculating the flow section variation amplitude of groundwater after the construction of the subway and the banked-up water levels after the construction of the underground stations, predicting variation of groundwater flow field after construction; making analysis and arrangement to the project’s influence on the groundwater quality; proposing specific groundwater environmental protection measures according to the studies. Come to the following findings:1. The groundwater type along the project is the Quaternary unconsolidated rock pore water, the rich aqueous of formation is strong, the salinity of groundwater is low, the chemical type of the phreatic water and the middle confined water is HCO3.The main sources of replenishment of groundwater are atmospheric precipitation, green land irrigation, groundwater runoff of mountainous area,the discharge way mainly includes evaporation, the flow downward and lateral runoff.2. The construction precipitation of underground stations and open-cut section is about 455~6075m3/d, the influence scope of precipitation is about 79~337m,the maximum influence range is in the Great South Gate Station which is 591 m,the maximum precipitation depth is 13.7~23.6m,which will temporarily affect the regional groundwater level and storage, with the completion of the construction and the end of precipitation, groundwater will be gradually restored in the role of air supply, the construction precipitation will not cause long-term adverse effects on the groundwater environment.3. Sand layers development area is key sections of land subsidence which is induced by precipitation. Sand layers development area of this project area are mainly distributed on 7 paragraphs, including both sides of Huazhang Street station, both sides of Tongda Street station, Jiajie station ~Longcheng street west station, both sides of South central Street station, Wang village south street station ~ South inner Street station, the Great south gate station, Xijianhe station, the proposed subway construction(especially in open cut station and tunnel) needs a large number of groundwater drainage, the land subsidence control measures should be strengthened in these sections of the process of construction; the sands development of the remaining sections is weak, the rock mass that the tunnel is crossing are mainly clayey soil and silty soil with poor permeability, the water inflow and groundwater level amplitude is small during excavation which is less likely to produce land subsidence.4. It may have a local impact on the regional underground runoff after the completion of the project. According to the forecast, the reduction of groundwater flow sections is around 17.4% after the completion of the project. There is a certain degree of impact on the local underground runoff by construction of the project, but compared with the overall regional groundwater environment, due to the subway structures accounted for only a small percentage of strati-graphic section, it will not produce obvious effect on groundwater runoff..5. Each underground stations structure will have some barrier impact on the underground runoff. The banked-up water levels of tunnel section is less than 0.083 m which is less than groundwater level changes of the wet and dry period. Thus, although the project may cause stagnation of the upstream runoff and the elevation of water level, but it did not change the groundwater flow field and is impossible to have an adverse impact on groundwater resources.