| As the country with the widest distribution of karst in the world,more and more deeply-buried long tunnels are built in the karst mountainous areas with China’s strong transportation network strategy.The construction of tunnels in karst mountainous areas usually causes water inrush disasters due to the geological environment of high water pressure and water-rich,and these disasters have the characteristics of large water volume and strong abruptness,which will be great harmful to engineering construction.Karst water is the material source of water inrush disaster.Studying its groundwater dynamic characteristics can predict water inrush disaster effectively,and provide a basis for the calculation of outburst prevention thickness between reserved karst cave and tunnel during construction.Therefore,it is a very critical and meaningful issue to study the karst groundwater dynamic characteristics and the thickness of the outburst prevention in the tunnel site area when constructing in the karst area.The Dongquan tunnel of Chongqing East Ring Road is located in Tongjing Town,Yubei District,and the tunnel is a typical karst tunnel,entering the mountain from the east side of Tongluoxia anticline perpendicular to the flank.Based on the Dongquan tunnel project,this thesis investigates the groundwater dynamic characteristics of the tunnel site area,the classification of water inrush failure modes and the calculation method of outburst prevention thickness on the basis of investigating the engineering geological conditions of the tunnel site area.The main research are as follows:(1)The engineering geological conditions,hydrogeological conditions and karst development characteristics of the tunnel site area are identified through site investigation and data collection,including topography,geomorphology,stratigraphic lithology,geological structure,meteorological and hydrological conditions,groundwater distribution,burial,recharge and drainage conditions,type of karst development,karst spatial distribution characteristics,etc.(2)In this study,a conceptual and numerical hydrogeological model is established based on the engineering geological conditions and hydrogeological conditions of the tunnel site area by means of the numerical groundwater simulation software GMS,which simulates the groundwater seepage field and recharge and drainage conditions in the study area,and analyzes the dynamic characteristics of groundwater,the head distribution characteristics along the tunnel and its relationship with the tunnel elevation.(3)The classification basis of surge water inrush mode is proposed,based on the type of surrounding rock,the spatial location relationship between the caves and the tunnel and the relative size of the water inrush disaster damage mode for classification through the analysis of the development pattern of cavities along the tunnel;(4)The physical model is simplified into a mechanical model,and the calculation method of the thickness of the outburst prevention between the tunnel and the surrounding hidden cavern is derived based on the theory of damage criterion in various modes,and the calculation method is programmed.On the basis of the groundwater dynamic characteristics,this study was conducted to find out the mileage of the tunnel that may be damaged by water inrush during the construction process and to calculate the thickness of the cavern that may be damaged by water inrush.The research results can provide the basis for the construction of Dongquan Tunnel,provide suggestions for the development and protection of hot springs,and also provide reference for the construction of other railway tunnels in karst areas. |
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