Multi-scale Evaluation Of Groundwater Environment On Mountain Mopan Tunnel

In southwest China, the terrain is steep, the geological structure is complicated, and the groundwater system is diverse. With the increase of southwest development speed, railway, highway, water diversion and other linear engineering of tunnel project also will increase. Complex hydrogeological units interact with tunnel project, the attention, groundwater problems brought by the project is more serious. Although numerical simulation has been widely used in hydrogeology research field, there are still certain defects, namely: When large area model of generalized complex aquifer medium over-fine subdivision is beyond the computer resource limit; Local small area simulation of boundary conditions are often difficult to control, which leads to the distortion. In view of this, this article based on the research of the hydrogeological characteristics in the study area, using the Visual MODFLOW simulation software to build complex hydrogeological conditions of spatial multi-scale hydrogeological model, and to predict the impact mountain Mopan tunnel construction the water diversion project in Yunnan. Further validation of multi-scale model for predicting complex hydrogeological conditions of tunnel engineering problems of groundwater has an important significance.Based on the regional geological survey in the study area, this paper combining the hydrogeological characteristics in the study area, the karst development and groundwater system, analysis the mountain Mopan tunnel hydrogeological problems, put forward the complex spatial multi-scale method of hydrogeological model, and establish a millstone mountain tunnel space multi-scale hydrological geological model. The main result of paper is as follows:(1) The complex geological structure in the study area, is located in Lancang River and Jinsha River and Red river watershed area, is mainly the tectonic denudation low hilly land. In the study area, there develop Yun Nan Yi group Triassic karst formations, karst develop medium. The types of groundwater are mainly bedrock fissure water and karst water. Karst water mainly accepts atmospheric rainfall recharge, is controlled by topography, lithology and structure factors, runoff and excretion through dissolution pores. Especially strong structural development zone is the advantage of groundwater seepage channel. Karst groundwater of Hedian street fault zone is more enrichment.(2) The mountain Mopan tunnel crosses karst and non-lava formation, and multiple aquifer units. Construction will change the natural runoff discharge conditions of groundwater and makes water tunnel centered constitute a potential new remit, thus affects tunnel crossing area of groundwater distribution pattern.(3) Spatial multi-scale hydrogeology model in the study area is composed of a regional large scale model and two multiple secondary scale sub models. Regional large scale model includes the mountain Mopan tunnel site area,it is to evaluate groundwater seepage field in the overall area, determine the boundaries of the model secondary scales; Two secondary sub-scale models include the new haizi reservoir areas and the crane factory areas, it is mainly to evaluate groundwater dynamic characteristics in key areas, and quantitate evolutionary trends accurately of prediction.(4) In the large scale model of mountain Mopan tunnel area, the hydraulic conductivity, water level, porosity data acquires by experiments and experience, and inverses by the PEST module. Groundwater seepage field and the actual situation are consistent. According to the preliminary prediction of large model, there determines two secondary scale model which is the new haizi reservoir area and the crane factory area. The new haizi secondary scale model simulation results show that the influence scope is 0.5-1km under the non-blocking condition, water level is reduced 5-15 m after two years, and new haizi reservoir leakages is weak. The crane factory secondary scale model simulation results show that karst segment is in karst groundwater runoff area, there have less effect on the discharge area of karst groundwater water level, and the water level in the recharge area is reduced in a certain extent. Under the non-blocking condition, crane factory well DL-W1 is reduced 44.1m in half a year, drawdown velocity is 0.156 m/d, and xiaoqing slope well DL-SZ12 is reduced 36.3m after half a year. Based on the simulation results of groundwater seepage field from the multi-scale model, the gushing water volume under the different control schemes is calculated by the Zone Budget module. No matter what kind of tunnel construction measures taken in the non-lava cave segment, the gushing water volume is small; in the karst segment, the gushing water volume of unit length is 6.18m3/d·m under the non-blocking condition, and the gushing water volume of unit length is 0.77m3/d·m under the local blocking condition.