Stress And Reliability Analysis Of Support In Initial Stage Of Tunnel Construction

In the process of tunnel construction,the initial support usually bears the load released by surrounding rock excavation and controls the further deformation of surrounding rock,so as to maintain the stability of tunnel and excavation face.Therefore,how to determine the reliability of the initial support in tunnel construction is an important topic of underground engineering research.Based on the Liyanlong No.2 tunnel project,this paper evaluates the stability of support and surrounding rock in the process of tunnel excavation according to the on-site monitoring data.At the same time,considering the change of initial support strength with age and the release of surrounding rock stress,the reliability of initial support in the process of tunnel excavation is studied.The main research contents are as follows(1)This paper introduces two mechanical modes of tunnel load structure method and stratum structure method,mainly expounds the existing calculation methods of surrounding rock pressure and lining stress calculation under load structure mode,and briefly analyzes three calculation methods of stratum structure.(2)Based on the analysis of the monitoring data of surrounding rock,the stability of support and surrounding rock is evaluated according to the displacement and deformation rate of support.At the same time,the deformation development trend of surrounding rock is analyzed combined with the vertical deformation curve of surrounding rock.(3)The finite element method is used to simulate the excavation and support of monitoring section to study the support stress and deformation.At the same time,the change of support stress under different support time and concrete hardening rate is analyzed.It is found that the best support time is when the initial stress release rate of surrounding rock is 60%～70%;By comparing the stress of primary lining under different hardening rates of concrete,it is found that the greater the hardening rate is,the greater the pressure on the vault is,and the greater the axial force is.However,due to the reduction of deformation,the bending moment of lining is also reduced,and the load bearing ratio of steel arch frame is also reduced.(4)The reliability method is used to evaluate the support stability in the process of tunnel excavation,and the curve of support reliability with time is analyzed.The research results show that the lining is most likely to lose stability within 2 to 7 days after the completion of support,and according to the monitoring results,the deformation rate of tunnel surrounding rock during this period is also large.Considering the reliability changes of concrete strength with age and surrounding rock stress release,it shows that the initial support will have a lower reliability extreme value before reaching the final stability,and the reliability contrast of arch waist position is particularly obvious,which should be paid attention to when analyzing the reliability of initial support of lining.In this paper,combined with the actual project,the analysis method of numerical calculation and monitoring measurement is used to analyze the support reliability in the process of tunnel construction.The research results have practical significance to guide the safe construction of the tunnel.