Seismic fragility analysis of mountain tunnels considering lining degradation

Mountain tunnels are typically located in complex geological environments, and the seismic performances of the tunnels are directly affected by the degradation of tunnel linings resulted from various erosions during the service life. The degradation laws of concrete and steel bars were determined by introducing the time-dependent concrete strength model and statistical characteristics of corrosion parameters of steel bars, and a time-dependent load carrying capacity formula of tunnel lining was established applying the load-bearing capacity equation of eccentric compression members and the time variable. According to the theory of seismic fragility analysis, an assessment process of seismic vulnerability of mountain tunnels considering lining degradation was proposed. A deep buried mountain tunnel in western China was taken as an example, a series of 2D dynamic time history calculations were carried out by using the incremental dynamic analysis method. An automatic extraction of the data and an automatic calculation of the maximum of damage index(DImax) during the seismic response process were implemented by using the Python programming language. Seismic vulnerability curves of tunnels with different service life were obtained considering the deterioration of concrete and the corrosion of steel bars. The results show that the vulnerability of the lining increases nonlinearly with increasing the service time. The damage probability of the lining increases slowly in the early stage of the service(0-50 years), while increases rapidly in the late stage of the service(50-100 years), showing that the longer the service time, the greater the effect of lining corrosion on seismic vulnerability of tunnels. Therefore, it is necessary to take into account the deterioration of linings for the risk assessment of operational tunnels. In addition, the shapes of the fragility curves of tunnels within the service time are similar for different surrounding rocks. The important effects of surrounding rocks and lining degradation on the vulnerability of tunnel structures are highlighted. The damage probability of the tunnel is larger for worse quality rock mass. The results can provide references for seismic vulnerability analysis and risk assessment of operational tunnels. © 2020, Science Press. All right reserved.