Study On Deformation Characteristics Of Metro Tunnel Structure In The Soil Of Karst Combined With Silt Stratum

With the rapid economic development, the scale of the city's subway construction is bigger and bigger, and building subway tunnel in the Soil of karst combined with Silt stratum becomes common. When there is a cave near the tunnel, especially in the case of the karst collapsing, because of the fluid-structure interaction effect, the integrity of its structure will be destroy, and the normal running of the subway tunnel will be in influenced; The subway tunnel in soft soil, especially when the soft soil is under the structure, the drainage consolidation of the silt soil makes the curvature radius of tunnel structure, slope and slope length change, makes the tunnel deform and the additional stress on the tunnel lining segment increase, and they will make the deformation of tunnel structure, additional stress and bending moment change, will affect the safety and durability of the tunnel. The operating metro line 5,line 6 and line 8 of Guangzhou all pass through the limestone area, where karst develop well.and Guangzhou belongs to the pearl river delta alluvial plain landscape, and the bad soil such as silt soil, distribute extensively. Combining with the data of the field of geological exploration, the thesis research the deform characteristic of the subway tunnel structure in the soil of karst combined with silt stratum based on the metro line no. 8 north extension period of Xiaoping station in Guangzhou, analyze the changing of the deformation of tunnel structure, additional stress and bending moment. With the method of general 3d finite element analysis software Midas GTS, make a comprehensive analysis, and suggest out the measures of dealing with the karst and silt. The research content and results are as follows:(1) According to the existing cave-collapsing theory and limit equilibrium condition of karst collapsing, analyze the causes of karst collapsing, the karst collapsing limit state, the safe thickness between tunnel and karst cave and the influence of cave collapsing conditionon the subway tunnel lining segment structure. Build the calculation model in the case of the cave losing it's balance.(2) According to the existing of silt soil consolidation settlement related theory and the basic model of silt soil drainage consolidation, set up the calculation formula of the consolidation settlement of the tunnel bottom silt soil. According to the basic principle of fluid-structure interaction, analyze the influence of the existing of karst and silt soil on the tunnel lining segment structure.(3) Based on the karst cave lost balance calculation model and silt soil consolidation settlement formula above, research the safe thickness between tunnel and karst cave and the mechanical condition of karst collapsing based on the actual engineering example the metro line no. 8 north extension period of Xiaoping station in Guangzhou. Calculate the deformation of the tunnel in the silt soil, and demonstrate it's ration by the finite element analysis.(4) With the large general finite element software Midas GTS, define determination conditions of the cave collapsing state, analyze the deformation of tunnel structure,additional stress and bending moment when change the distance between the bottom of the tunnel structure and karst cave and the cave diameter. Analyze the influence of the silt soil drainage consolidating on the subway tunnel lining segment considering the change of underground water level.(5) According to the analysis above, suggest the measures of dealing with the karst and the silt soil in the case of the tunnel passing through the combinatorial soil layer of karst and silt soil.