| China is one of the countries with widely distributed karst in the world,Karst area accounts for about 20% of China's total area.In the recent years,As the continuous growth of economic development and the western development strategy gradually advanced,tunnel engineering plays an important role as an integral part of the infrastructure projects.Thus,a large number of underground projects were built in karst areas;the stability problem of the tunnel in karst area is becoming more and more prominent.Geological disasters generated by karst have brought great difficulties to the construction of tunnel projects,which caused huge economic loss.Therefore,in order to ensure the smooth construction of the tunnels in karst area and the safety of the operation stage,it is necessary to study the tunnels in the karst area.This research is based on the actual engineering background of Xixia tunnel,this research takes the corresponding treatment measures to the karst disaster problems of the highway tunnel construction in karst area,the numerical stability of the tunnel in the karst section is compared with field monitoring.Specific research contents and conclusions are as follows:(1)The karst general development conditions and its soluble mechanism from the structure of rock are summarized.The general rule of karst development is analyzed from the two aspects of karst morphology and classification,and the karst is divided according to the exposed conditions and geological structure of the rock.Construction engineering projects in karst area are summarized by engineering geology problems,and the mechanism of karst water bursting from the mechanics and behavior characteristics are analyzed,based on the Bernoulli's energy equation,this paper derived the calculation formula of water flow velocity and flow rate.(2)The evaluation methods of the cave foundation stability under the condition of complete roof and incomplete roof are analyzed,and the calculation formula of the minimum safe thickness of the karst roof is obtained.Some problems of the stability analysis of karst caves are analyzed by using the finite element method,and mechanical model and selection of related parameters are studied.(3)Taking the actual engineering of Xixia tunnel as an example,the water inflow of highway tunnels is forecasted and the method of poor geological evaluation and its pretreatment plan are given.In order to solve the problem of small karst holes and roadbed water breakthrough in the construction of karst section,the paper gives the control plan of sealing and steel pipe piles reinforced roadbed.For long-big karst cave of karst section in the process of tunnel construction,this paper proposes a new type of pile cap across the cave tunnel supporting structure,and gives the detailed construction procedure,analyses its beneficial effects and working principle,to solve the problem of tunnel across the long-big cave provides a new train of thought.(4)The numerical simulation method is used to analyze the situation of the Xixia tunnel after different disposal techniques.The variation law of the plastic zone and the displacement of the surrounding rock are obtained.Through the monitoring results of steel pipe pile foundation,the stability of the tunnel roadbed is evaluated,and the stability of the steel pipe piles is verified. |
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