Study On Safety Distance Between Tunnel And Karst Cave And Treatment Technology Of Cave

With the development of infrastructure in Western China,Subway construction and the underground pipe gallery construction has become the key project.However,the complex and changeable karst geology has become a huge challenge for the development of rail traffic construction.If the safe distance between the cave and the tunnel could be predicted reasonably,and the hidden caves be treated properly.It would relate not only to the safety of tunnel construction and operation,but also to the safe of surrounding buildings.In addition,the high construction cost can be reduced.Therefore,the safe distance between karst cave and tunnel will be studied systematically in this paper.And the treatment technology of karst cave will be researched.The main work is as follows:(1)At first,the stress change of surrounding rock has been discussed basing on rock failure theory.When the plastic zone of the karst cave is connected with the tunnel’s plastic zone,the shortest distance between the cave and tunnel is the safety distance.Seven influence factors related to safety distance were written in the next.(2)Considering the spatial effect of shield tunnel and karst cave,a three-dimensional finite element numerical model of shield tunnel excavation has been established.The different kinds of caves have been discussed during tunnel excavation.These caves include different amounts of cave,different location of cave and different filling of cave.Displacement field,stress field and plastic zoon of the surrounding rock of tunnel have been analyzed.As a result,multiple caves have a greater impact on tunnel than single cave.The effect of cave location to the tunnel is different.And the filling material has less influence on the stability of the cave.(3)The specific relationship between safety distance and the influence factors have been studied.The factors include parameters of surrounding rock,lateral pressure coefficient,the buried depth of the tunnel,and the span of cave,the width of cave and relative position of cave.Uniform design has been used to design a numerical simulation test about the safety distance and factors.The numerical simulation test included 48 groups.Each kind of cave location needs 16 groups of tests.In order to get the safety distance in each test,the distance between the double cave and the tunnel will be reduced until the plastic zone of the karst cave is connected with the tunnel’s plastic zone.Stepwise regression method was used to analyze the relationships between factors and safety distance.And the prediction formulas of safety distance will be proposed.(4)The prediction formulas of safety distance was used in the project example.An example of tunnel excavation in karst area of Nanning city has been presented.Three kinds of karst caves have been predicted which located above the tunnel,beside the tunnel and below the tunnel.Compare with the conditions in design and the project,finally,the project application shows the feasibility and effectiveness of the prediction formulas.The existing karst treatment technology and has been summarized.These studies provide a reference for the karst tunnel construction in the future.