Safety Assessment Based On Tunnel Secondary Lining Surface Stress State Of South Tunnel

With sustained economic development,the improvement of the comprehensive national strength and rising high-tech,our tunnel and underground engineering has an unprecedented rapid development.Number of operated tunnel is increasing rapidly,and also attracted great concern for the safety of the operated tunnels.Since our country started late in the tunnel maintenance and monitoring,the current standards and norms of the operated tunnel monitoring technology and safety assessment method have not been proposed.This paper relies on Chongqing South Tunnel disease monitoring and safety assessment project,and studies of tunnel secondary lining surface stress.Based on limit analysis finite element method,using a secondary tunnel lining surface stress assess tunnel safety which will realize the combination of tunnel monitoring and measurement technology and quantify safety assessment,providing a more simple and effective way to assess the safety of tunnels.Combined with the actual situation of South tunnel,using ANSYS software studies secondary lining of operated tunnel in two parts.(1)Focuses on three factors included surrounding rock creep,less secondary lining thickness,holes behind secondary lining.To simulate surrounding rock creep,this paper describes the types of common creep models and simulations based on ANSYS software’s creep implicit principle,determine using visco-elasto-plastic model for simulation of surrounding rock rheology.Through comparative analysis of the results obtained: surrounding rock creep make the maximum principal stress of tunnel secondary lining increasing firstly then showing attenuation trend,eventually stabilizing at about 600 days;less lining thickness and holes behind lining,bring stress concentration at the secondary lining where the diseases exist.(2)According to limit analysis finite element method to obtaine the secondary lining surface stress when South tunnel is calculated with different security reduction coefficient,and curve fitting secondary lining surface stress and security reduction coefficient.After the completion of the tunnel,without considering the case of external load,secondary lining surface stress does not change,but the actual monitoring can detect changes in the secondary lining surface stress.Through the analysing under different security reduction coefficient the tunnel secondary lining surface stress,obtained the relationship between the variety of tunnel arch waist at the secondary lining surface stress and reduction coefficient,and obtained the variety of secondary lining surface stress threshold before the tunnel lost stability.And asess the South tunnel safety based on the calculation result and South tunnel long-term monitoring data.This paper based on Chongqing South tunnel,research on operated tunnel secondary lining surface stress,and obtained the relationship between the arch waist lining surface stress and the reduction coefficient.And obtained a threshold value of tunnel arch waist second lining surface stress,which provides a basis for maintenance and safety assessment of Chongqing South tunnel.It also provide a reference for other similar projects.