Analysis Of Surface Subsidence And Tunnel Stability During The Shallow Tunnelling Construction

In recent years,the shallow-buried tunnelling method applied in the construction of urban underground railway tunnel is becoming more and more widely in our country,but the problems of surface subsidence and tunnel stability will occur during the excavation of tunnel by shallow-buried tunnelling method.Owing to excessive surface subsidence,the buildings or structures will be unstable,and the improper operation or supporting untimely will lead to instability and collapse of tunnel.However,because of the complex construction site of city and the bad conditions of hydro-geological and engineering geology,the problems of surface subsidence and tunnel stability in the process of tunnel construction is more prominent;therefore the research is about what influence the shallow-buried tunnelling method has on surface subsidence and tunnel stability,which is very important and significant.Based on the extensive research on the domestic and foreign literature and material,taking Kunming metro tunnel as the engineering background,using theoretical analysis,numerical simulation and field measurement,This thesis conducts a research deeply and systematically about the problem of surface subsidence and tunnel stability in the construction of shallow buried tunnel.The main results and contents are as follows:(1)It analyzed and summarized the main factors affecting the surface subsidence and tunnel stability during shallow tunnelling construction,and the forms and features of damaged tunnel;meanwhile analyzed theory of surface subsidence based on three aspects respectively which are the instability of micro-structure of stratum,the loss of stratum and soil consolidation subsidence.(2)It simplified lateral surface subsidence formula of stochastic medium theory;through changing the original assumptions of stochastic medium theory for that soil will be drained and consolidated due to disturbance during the shallow tunnelling construction,modified the simplified formula of stochastic medium theory which is used to calculate the lateral surface subsidence,and finally got simplified and modified formula;the compared of simplified and modified formula and Peck's formula which modified by the Liu Jianhang,verified the correctness of the simplified and modified formula which calculate the lateral surface subsidence.(3)It established the progressive hierarchical structure model of analytic hierarchy process which is used to evaluate tunnel stability during shallow tunnelling construction,and calculated the weights of factors at all levels;modified the result which is come from evaluating of tunnel stability during shallow tunnelling construction using analytic hierarchy process with the strength reduction method and displacement reduction method,and obtained the modified formula.(4)Through the three-dimensional numerical simulation to calculate the value of lateral surface subsidence caused by construction of tunnel and the safety factor of tunnel stability in Kunming metro tunnel,the compare of measured values and numerical values and theoretical values which is calculated by the simplified and modified formula of lateral surface subsidence verified the practicability of the simplified and modified formula of lateral surface subsidence;the final safety factor of tunnel stability is 1.12,that is to say,the possess of shallow tunnelling construction is under general stable state.