Investigation Of Groundwater Inflow And The Influence On Environment During Tunnelling In Mylonite Fault

Groundwater inflow during tunneling is one of the geological hazards,especially for the mylonite fault.This study was undertaken for the following purposes: i)to evaluate the groundwater inflow during tunneling in mylonite fault,and ii)to analyse the influence on environment when groundwater inflow was occurred.Research methods such as field measurement,theoretical analysis,and numerical simulation were employed.The finite difference model was built to calculate the hydrogeological parameters during the mylonite fault.Then an analytical approach to evaluate groundwater inflow was proposed.Groundwater inflow and the influence on environment were analysed by finite difference model(FDM)and finite element model(FEM).The concluding remarks of this study are summarized as follows.(1)The pumping tests during mylonite fault were analysed to ascertain that the fissures of mylonite were not uniform.Both analytical methods and numerical simulation approach were used to calculate the hydrogeological parameters during fault.The results showed that the simulation based on the finite difference model was able to resasonably derive the hydraulic parameters for a given geological stratum in the studied area and could capture the non-uniform fissure development.(2)An analytical approach to calculate groundwater inflow was proposed,in which time,anisotropy of aquifer,groundwater level,exvavation length,radius of tunnel,and thickness of aquifer were considered.The aforesaid appoarch was deduced by the point superposition method,Laplace transform,definite integral and etc.Finally the relationship between S(t)/Q(t)and time can be obtained.The above proposed formula was adopted for the mylonite fault,and the law between the groundwater inflow and time also can be obtained under the differnet drawdown,hydraulic conductivities and thickness of aquifer.(3)The finite difference model was adopted to evaluate the value of groundwater inflow.Both water budget and similar waterlevel were simulated to ascertain that the calculated seepage filed agreed with the actual seepage filed.Then the groundwater inflow was calculated.The results showed that two stages containing the instantaneous water inflow and stable water inflow were divided.The relative error between simulated and actual groundwater inflow was only 4.4%,which implied that the numerical simulation was worth trusting.(4)The finite element model was also used to calculate the groundwater inflow and analyse the influence on environment during water inrushing.The solid elements were adopted to simulate excavation face,and the zero pore pressure was set in the aforementioned excavation face to simulate the water inflow.The results showed that the linear relationship between the cumulative groundwater inflow and time was exsited.The water velocity rise quickly,then fall down slowly and finially was stable.The pore pressure in the vinicity of excavation face was little and the settlement above the exvavation face was the maximum.And the displacement,pore pressure of segment was the maximum during the excavation face.