| In recent years,more and more attention has been paid to the development and utilization of underground space.As an important project of underground space,the safety of tunnel construction has been widely concerned.Under the complex geological conditions such as Badong Formation,there are many tunnel surrounding rocks with strong creep characteristics,and the reliability of support body and section stability have obvious time effect characteristics.Therefore,in the process of advancing the face,the collapse and other tunnel engineering accidents caused by the destruction of the support structure of the completed support section are increasing day by day.But at present,there are few researches on the collapse accident analysis of tunnel and underground civil air defense project,that is to say,the research on the time effect reliability of the support body,that is,the risk prediction and effective safety assessment of the tunnel project are still insufficient.In this paper,based on the engineering research background of the excavation project of baicungou shallow buried large-span high-speed railway tunnel in Fengjie County,Chongqing,the typical sections of DK718 + 800,DK718 + 751.7 and DK718 + 750.8 are selected for research.With the aid of ABAQUS and MIDAS / GTS finite element analysis software,considering the creep action of surrounding rock under complex geological conditions,this paper studies the time effect reliability of initial support during tunnel construction under the geological conditions of Badong Formation.The main research contents are as follows:(1)This paper first introduces the creep characteristics of the surrounding rock of the tunnel,then expounds the interaction process between the initial support and the surrounding rock,and finally analyzes two basic creep processes of the rock,namely,stable creep(decaying creep)and unstable creep(decaying creep).Then it introduces the general method to evaluate the reliability of tunnel engineering.Because the settlement and convergence around the tunnel can reflect the mechanical properties and stability of the support structure in the process of tunnel construction intuitively and objectively,this paper focuses on the displacement to study the time-dependent reliability of the initial support structure of the tunnel,and defines the time-dependent failure probability of the support structure based on the convergence constraint principle,At the same time,the method to determine the limit displacement is introduced.(2)The section DK718 + 750 ～ DK718 + 800 of baichugou tunnel is selected and modeled with MIDAS / GTS software.CD method,bench method and full section method are selected to analyze the displacement changes around the tunnel under various working conditions,and then the position of the section with the largest deformation,i.e.the unfavorable section with the greatest risk,is determined when different construction methods are adopted.(3)The typical sections of baichugou tunnel DK718 + 800,DK718 + 751.7 and DK718 + 750.8 are selected for modeling and analysis with ABAQUS software.The key positions of arch crown,arch shoulder,arch waist and arch foot are selected to analyze the stress change and deformation of each characteristic point of the support structure in different directions with the advance of the face.Finally,the displacement time curve of each section is polynomial fitted.According to the fitting equation,the time-dependent failure probability of each observation point is calculated respectively,and the timedependent failure probability of tunnel dangerous section in different excavation process is obtained,and then the time-dependent reliability and stability of tunnel section are judged.The time-dependent failure probability can realize the dynamic evaluation of tunnel engineering risk,and comprehensively predict the risk of different time points in the whole process of tunnel construction,which is of great significance for the design optimization and construction risk avoidance of underground tunnels. |
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