Study On Characteristics Of Groundwater Transport And Its Environment Effect During Constructing Tunnel Group In Fragile Ecology Region

Engineering construction is faced with three major problems: the safety of engineeringconstruction, the economy of engineering construction, the protection of environmentsurrounding engineering facilities.“Safety”,“economy” and “environmental protection” arethe body of the unity of opposites. How to make them mutual coordination is every engineer’sproblem. Wushaoling tunnel group is located at transition zone of many fragile ecologicalregions. However, this kind of tunnel is constructed on the crustal derm of the most activegroundwater. The construction will make the tunnel become influx place of surface water andgroundwater, or become a new discharge passage, which will influence the safety of tunnelconstruction and destroy ecological environment. Through field observation of regionalgroundwater environment and regional three-dimentional seepage field numerical modeling,we analyze the characters of regional groundwater movement, make quantitative evaluationon the eco-environmental effect of groundwater movement caused by tunnel groupconstruction, and put forward long-acting waterproof and drainage measures on the charactersof regional groundwater movement. Main research results are as follows:1. Through field investigation and systematically summarizing predecessors’ researchresults, the paper summarizes regional environmental geological characters of Wushaolingtunnel group from four aspects: physical geography, regional geology, regional hydrogeology,ecological environment. In this region, the types of terrain and landform are complex.Geological structure is complex. Lithology and lithofacies greatly change. Geologicalenvironmental conditions are complex. Ecological environment is fragile.2. Through field observation on regional groundwater environment of Wushaoling tunnelgroup, that is including dynamic observation on soil moisture and groundwater level, weconfirm relationship between plant and soil moisture dynamic variation. Plant growth, whichis mainly influenced by meteoric water and soil moisture dynamic variation, has littlerelationship with phreatic water. The variance coefficient of various plant types’s soilmoisture decreases with increasing of the soil depth in the region. The buried depth is deeper,the variation of soil moisture is less. Time feature shows obvious seasonal variation, whichcan be divided into water loss, water collection, recession flow, and water stability. The lossof soil moisture can get through plants transpiration, soil surface direct evaporation andevaporation after soil moisture confluence. However, supplying soil moisture only has oneway of meteoric water. 3. Based on creating conceptual model and numerical simulation of three-dimensionalseepage field, we use MODFLOW to achieve three-dimensional seepage field numericalsimulation. According to the data of long year average precipitation, creating unsteady flowmodel under long year average condition before tunnel construction, we calculate and getregional groundwater initial flow field. Tunnel construction has an influence on groundwaterseepage field, which is controlled by different formation permeability and tunnel drainage’sheight difference. According to calculation, with the promotion of tunnel construction process,the decrease of groundwater level gradually increases. Cone of depression also graduallyextends to two sides of tunnel, except that it gradually develops along tunnel trend. WhenWushaoling tunnel group will have been completed for ten years, each tunnel phreatic waterlevel will recover a little.4. According to engineering analogy and actual situation of the region of Wushaolingtunnel group, we create the index system of eco-environmental effect evaluation caused bygroundwater movement in the construction period of Wushaoling tunnel group. Thisevaluation index system contains four subsystems: physical geography, regional geology,eco-environment, tunnel construction. The subsystem of physical geography contains slope,aspect, absolute height, annual average precipitation, and annual average evaporation. Thesubsystem of regional geology contains fault fracture zone development degree, folddevelopment. The subsystem of eco-environment contains soil types, vegetation coverage.The subsystem of tunnel construction contains length of tunnel, structural approach limitwidth of tunnel, tunnel construction method, tunnel max buried depth, design of tunnelwaterproof and drainage. According to matter element extension model, we use simplecorrelation function to confirm every index weight and comprehensively evaluate theeco-environmental effect caused by groundwater movement in the construction period ofWushaoling tunnel group. Eco-environmental effect is judged belongs to grade two, that isweaker. But it is partial to grade three, that is medium. Strictly speaking, it belongs to grade2.581.5. Aiming at Wushaoling tunnel group which is located at alpine fragile environment,based on research results on the characters of regional groundwater movement of Wushaolingtunnel group, we propose corresponding specific technical parameters of grouting forstopping up water in rock mass, structure waterproofing, drainage system setting.