Research On Influence Of Tunnel Construction With Mining Method On Groundwater Environment In Weathered Granite

The tunnel construction will disturb the balance of groundwater environment,cause the loss of groundwater resources,and have bad influence on groundwater environment.At the same time,water inflow into tunnel will also endanger the tunnel construction.Compared with shield method and TBM,mining method causes more serious disturbance and damage to the surrounding rock of tunnel and then an obvious excavation damage zone is formed.The permeability of surrounding rock in the excavation damage zone is enhanced,aggravating the loss of groundwater.Granite outcrops widely in southern China,especially in southeastern coastal area,which is easy to be affected by weathering.The permeability of granite is closely related to its weathering degree,and the construction with mining method has different influence on the permeability of granite with different weathering degrees.Therefore,it is difficult to evaluate the negative effect of the groundwater environment and design the waterproof and drainage system for the tunnels constructed with mining method in water-rich weathered granite stratum due to the differential weathering of granite and the influence of the mining method.The research on the influence of tunnel construction with mining method on groundwater environment in weathered granite can not only provide a guidance for reducing the negative effect of construction on groundwater environment,but can provide a reference for the design of tunnel waterproof and drainage system,which has important academic and practical significance.The core of this research is the influence of tunnel construction with mining method on groundwater environment and the engineering background of this research is weathered granite tunnel.Through the field investigation,theoretical analysis,indoor and outdoor test and numerical simulation,the influence of tunnel construction with mining method on groundwater environment in weathered granite was studied.The main research works and results of this paper are as following:(1)The general situation and engineering geological condition of study area were investigated in detail.The data were collected and analyzed from various stages including field investigation,design,and construction.The above works provided basis for studying the influence of tunnel construction with mining method in weathered granite on groundwater environment.(2)The variation of permeability of granite with different weathering degrees before and after construction with mining method was studied by in-situ and indoor seepage tests and theoretical calculation.The influence of weathering degree and construction with mining method on permeability of granite was analyzed from the aspect of microstructures and mineral composition by rock flake polarized light microscope test.The scale of excavation damage zones induced by mining method was determined by wave velocity test.(3)Considering the effect of excavation damage zone,the influence of tunnel construction with mining method in weathered granite on seepage field was studied by numerical simulation.The variations of water inflow into tunnel,groundwater level,pore pressure,and velocity of groundwater in different stages of tunnel construction were determined,and the sensitivities of seepage field to a range of influencing factors during tunnel construction were analyzed.(4)Based on the complex variables and the theory of seepage mechanics,the analytical solutions for seepage field of tunnels with controlled drainage were derived and the sensitivity of seepage field to the variation of grouting parameters was analyzed using the proposed analytical solutions.The seepage fields of tunnels with different drainage systems,including controlled and full drainages,were compared and analyzed by the analytical solutions.The seepage flow and water head on lining of tunnel without drainage were calculated and the effects of grouting circle and excavation damage zone on the seepage field of tunnel without drainage were analyzed using the analytical solutions.A novel waterproof and drainage system,which is suitable for subway tunnels with large buried depth below groundwater level,was proposed.(5)Based on the effect of tunnel construction with mining method on seepage field and the domestic and international research results of the evaluation of negative effects of tunnel construction on groundwater environment,the evaluation index system for negative effects of tunnels construction on groundwater environment was established and the grading standards for evaluation index and negative effects on groundwater environment were proposed.The index weight was determined by analytical hierarchy process and the evaluation indexs were quantified by fuzzy comprehensive evaluation.Taking the MAPGIS K9 software as basic platform,a system for evaluating the negative effects of tunnels construction with mining method on groundwater environment in weathered granite was developed using the Visual C# language.(6)The research results were applied to the tunnels in the 12 section of Guangzhou Metro Line 21,and the negative effect of construction with mining method on groundwater environment was evaluated by the evaluation system.Then,the results of evaluation system were compared with the results of numerical simulations and field investigation,which indicated the results of evaluation system were reliable.Based on the results of evaluation system and numerical calculation,according to the negative effects of construction on groundwater environment and the water head on lining,the corresponding type of waterproof and drainage system and construction technology were proposed for different segments of tunnel.