Three-dimensional Simulation Of Groundwater Movement In Tunnels Crossing Karst Pipeline Medium

The traditional groundwater numerical simulation uses MODFLOW to simulate the groundwater flow field,generalizing the aquifer system into an equivalent continuous medium,and the groundwater flow is the Darcy flow.However,in the southwestern region with multiple karst medium structures,the development of a large number of pipeline dark rivers makes the groundwater have the flow characteristics of the Darcy flow and the non-Darcy flow.However,MODFLOW cannot describe this feature.The US Geological Survey developed a MODFLOW-CFP(Conduit Flow Process)module based on MODFLOW to deal with the complexities of karst non-Darcy flow and multi-porous media.The CFPM1 mode enables traditional linear laminar flow models and discrete pipeline networks.Coupling.The CFPM1 mode needs to assign the properties of each pipeline,and realize the water flow transformation through the critical Reynolds number of the pipeline and the water exchange.Based on the feasibility study project of Chongqing Mingyuexia anticline potential traffic corridor,this paper uses MODFLOW-CFP to construct a typical karst aquifer system and discusses the key parameters of pipeline flow simulation.According to the numerical model of the regional and site scales in the southern section of Mingyue Mountain,the model of groundwater flow in the southern part of Mingyue Mountain was constructed by using MODFLOW-CFP.The CFPM1 model was used to characterize the karst pipeline and analyze the regional groundwater flow field.The model provides the model background such as boundary conditions;the two schemes of the tunnel site model A and B are proposed,and the effects of tunnel excavation under the pipeline section and the selection of tunnel elevation on the groundwater flow field and the tunnel water inflow are simulated.The main findings are as follows:(1)MODFLOW-CFP realizes the groundwater flow model of dual structure fissure-pipeline in karst aquifer system.Fracture system is generalized as equivalent porous medium.Pipeline system is generalized as multi-segment interconnected structure with CFPM1 module.These two systems are coupled by exchange flow.By constructing a typical karst water-bearing unit,,the effects of fissure media,flow field background and pipeline parameters in karst aquifer are analyzedbased on MODFLOW-CFP module.(2)Taking the southern section of Mingyue Mountain as the research area,the numerical model of regional and site scale is established.The regional model takes the complete hydrogeological unit where the pipeline is located as the simulation scope,and adopts MODFLOW-CFP to describe the karst pipeline in detail,focusing on the pipeline flow situation and the characteristics of regional groundwater flow.The site model is narrowed down to the tunnel site area.And the model is subdivided into subdivisions.The third boundary drainage Drain module is used to generalize the tunnel.The model mainly focuses on the prediction of tunnel water inflow and influence of the tunnel excavation project to the pipeline and internal water.(3)In the construction of the regional model,MODFLOW-CFP is used to describe the typical karst dark river pipeline in the Huanhuadong-Zhangguan section.Through the actual investigation,drilling data and tracer test,the characteristic parameters of the pipeline medium are obtained.The CFPM1 mode is used to characterize the pipeline section in the area,and the water level result of the observation hole is fitted,and the simulation result of the regional model is extracted as the site of the tunnel area.The model provides strong background conditions.(4)Two schemes of site scale numerical models have been established:in scheme A,the tunnel is located at the lower part of the pipeline section(rock peak-dry tunnel).While in scheme B,the underground river pipeline section has been avoided and the elevation of tunnel according to the vertical zoning characteristics of karst has been discussed.This paper mainly analyses the changes of groundwater level around the tunnel site,the water body in the pipeline and the water inflow of the tunnel.This paper also provides a reference for the planning and site selection of the tunnel.By comparing the simulation results of site model,scheme B is superior to scheme A in terms of the variation of groundwater level,the influence of water body in pipeline and the water inflow in tunnel.In scheme A,the tunnel passes under the karst pipeline section,which can cause the disaster water body in the pipeline to converge to the tunnel,the tunnel water inflow is 44210.54m~3/d.In the end,the karst hidden river section may be influenced.The spatial location simulation results of the tunnel in Plan B show that the tunnel elevation is 320-300m,so the disturbance of the tunnel to the surrounding groundwater and the water body in the pipeline is slight.The minimum water inflow is 5738m~3/d,which can be used as the optimal elevation section for tunnel planning.