| China is one of the most widely distributed and largest carbonate rocks in the world.According to historical data,the total area of carbonate rocks in China accounts for about one third of the total area of China.Karst is the most difficult engineering geological problem in the development of urban underground space.In the past urban karst area engineering construction,the two-dimensional(various scale plan,geological section)and static expression method are used to analyze and explain the karst development law according to the site survey data for the unknown karst.This is difficult to express the extremely irregular spatial form of karst cave intuitively and comprehensively.With the development of modern geological information technology,it is of great geological significance to change karst from traditional fuzzy character qualitative description to digital,quantitative and fine display.The karst area in the city is prone to collapse under earthquake,which causes major disaster accidents.Karst has amplification effect on subway tunnel under earthquake action,especially for Metro in urban karst area.If earthquake occurs,karst in untreated area will directly affect the safety and stability of subway structure,and it is difficult to repair once damaged.At present,the research on seismic response of shield tunnel in karst area is relatively lacking.The main research results are mainly to simplify the simulation of karst tunnel into single karst tunnel,and not to consider the spatial distribution characteristics of karst tunnel.In fact,the cave distribution is very complex and the shape is irregular.Therefore,how to simulate the karst cave distribution more closely is of great practical significance to the study of karst engineering problems.Based on the existing achievements of Guangzhou Metro Line 9,this paper studies the seismic dynamic response characteristics of metro tunnel around the mechanism of random cave formation.Based on previous studies,the concept of volume ratio of karst tunnel is introduced,the basic characteristics of karst cave are determined according to mathematical relationship,and the mechanism of random cave generation is established.Combined with the relevant information of typical shield interval of Guangzhou Metro Line 9,the random generation mechanism of karst tunnel is established The 3D geological model of cave algorithm is generated.The seismic response characteristics of shield tunnel are studied by using finite element model,which conforms to the free field boundary conditions of subway tunnel,seismic wave baseline drift correction and filtering.The main contents and achievements of this paper are as follows:(1)Research on the random cave generation algorithm: Based on the concept of volume ratio of cave,a set of random cave generation algorithm is established by using the appropriate mathematical principle.Considering the relationship between the random shape,size and spatial distribution of the cave,a set of random generation cave algorithm can be established which can realize random location,random shape and random large and small(within the actual size range).It can be used in geological modeling and 3D finite element calculation.(2)The study of geological modeling based on the random generation of karst cave algorithm: extracting the drilling information,exposing the soil layer information and the information of the interface of each layer in the typical shield interval of Guangzhou Metro Line 9,and processing accordingly.The 3D geological model of randomly generated karst cave is established,which can directly describe the distribution relationship between the excavated layer and the untreated cave,and realize certain degree of information Degree 3D visualization.(3)Study on the seismic dynamic response characteristics of subway tunnel: the seismic response characteristics of shield tunnel under different volume ratio are studied by using the stochastic 3D geological body finite element model of the cave.Firstly,under different seismic wave,the change of volume ratio of the cave will cause the change of the relative acceleration and relative displacement of the tunnel segments along the tunnel longitudinal direction,but the change will be made The second is that the time history curves of the arch top,waist and arch bottom of tunnel segments are almost coincident under the same earthquake wave.The influence of the change of volume rate of the tunnel tunnel segment along the longitudinal direction of the tunnel is limited by the change of the volume rate of the tunnel under the action of earthquake.The influence of relative acceleration and relative displacement can not be considered in such calculation;thirdly,when the same seismic wave is applied,the maximum principal stress of the tunnel segment will increase with the change of the volume ratio of the tunnel to exceed the tunnel itself The ultimate tensile strength of concrete indicates that the volume ratio of the tunnel tunnel will affect the safety and stability of the tunnel segments,which leads to the local small range of the tensile crack.Except for the small part,the maximum main stress of the rest parts is less than the ultimate tensile strength of the segments.There is no maximum main stress in the key parts such as transverse or longitudinal staggered joint splicing,and the tunnel can be operated safely.When the cave is in the lower level,if the height of the cave is 2-4m,the treatment of the cave may not be considered;however,the cracks in the segment will cause a large potential safety hazard to the whole tunnel under the long-lasting earthquake.Therefore,some areas with wide karst distribution may consider the corresponding seismic evaluation of the tunnel to ensure the safe operation of the tunnel. |
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