| The exposed limestone area in Guangxi reaches 120000 km~2,which is one of the most developed and typical areas of karst in China with vast underground caverns and large underground river basin.There are 6 underground river systems in the karst area of the Duba expressway,including Disu underground river system with a basin of 1000 km~2.Due to the extremely developed karst along the highway and the complex hydrogeological conditions,it is very easy to casue water gushing disaster in tunnel construction,which significantly affects the construction safety.In this paper,the following research work is carried out in order to study the Nongmo tunnel:(1)Identify the geological conditions,karst hydrogeological conditions of the tunnel zone;(2)Establish the numerical simulation natural seepage field in the tunnel zone and simulate the effect of tunnel excavation on the seepage field in the tunnel zone.(3)Analyze the geological model of tunnel water gushing,and evaluate the risk of water gushing in each section of the tunnel.(4)Calculate the flow of the tunnels in different ways obtaining the tunnel inflow through comparative analysis.The main research achievements:(1)The karst development is high and the geological conditions are complex in the tunnel zone.The surrounding rock of each section of the tunnel is divided into?,?,?level,through shallow seismic method and the physical and mechanical parameters of surrounding rock.The main type of ground water in tunnel zone is karst water,and its supply source is mainly atmospheric rainfall.The karst water mainly flows to the east and west valleys,the Xialou underground river and the Latang-nanjiang underground river as the excretory channel,and finally into the Hongshui river.According to the karst hydrogeological conditions,the tunnel zone is divided in to the western hydrogeological unit and the eastern hydrogeological unit.(2)In this paper,the karst hydrogeological conditions of the tunnel zone are analyzed,and the spatial structure of aquifer,the boundary conditions and the source transfer items are reasonably generalized,and the hydrogeological conceptual model of the tunnel zone is established.On this basis,the model space and time are separated,and the relevant hydrogeological parameters are determined.Establish the numerical model of natural seepage in the tunnel zone.Analyze the effect of tunnel excavation on the seepage field in the tunnel zone,from the perspective of the change of seepage field,the effect of tunnel drainage 1 year completely on seepage field is obvious,the tunnel has a tendency to form a linear landing funnel,and the water level in each section of the tunnel at most decreased by 20-30m.After two years of complete drainage of the tunnel,the line falling funnel formed in the tunnel section is more obvious,and the water level in each section of the tunnel at most decreased by 5-10m than that of the first year;After five years of total drainage,the seepage field in the tunnel zone has basically stabilized,and the water level in each section of the tunnel at most decreased by 35-50m than that of the natural seepage field.(3)There are 3 geological models of the tunnel water gushing,namely karst fissure water-bearing structure model,karst pipeline water-bearing structure model,fault-karst pipeline water-bearing model.Among them,the water-bearing structure model of karst pipeline and the water-bearing model of fault-karst pipeline are more harmful.Evaluate the risk of water gushing in each section of the tunnel by hierarchical analysis-fuzzy mathematics comprehensive evaluation.Among them,the evaluation level of K363+880~k364+370 section is the highest,which is?level,the water gushing level is extremely high,and the water inflow is greater than10~4m~3/d.The evaluation level of K364+740~K364+835 section is the lowest,which is?level,the water gushing level is extremely low,and the water inflow is less than10m~3/d.The evaluation level of the remaining sections is?level,and the water gushing level is high,and the water inflow is 10~3~10~4 m~3/d.(4)Precipitation infiltration method,groundwater dynamic method and numerical simulation method were used to calculate the water inflow in each section of the tunnel.By comparison and analysis,the evaluation results of the tunnel risk are evaluated by the analytic hierarchy analysis-fuzzy mathematics,and the water inflow in each section of the tunnel is determined.In each section of the tunnel,K363+880~K364+370 section is the largest part of the water inflow,and the water inflow is 15646.27 m~3/d.There is no water in K364+740~K364+835 section,and the water inflow in the other sections of the tunnel is 2935.57~9890.97 m~3/d.The largest water inflow of unit length section is K363+800~K363+880,and the water inflow of unit length is 49.79m~3/d.There is no water in K364+740~K364+835 section,and the water inflow of unit length in the other sections of the tunnel is 5~31.93 m~3/d. |
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