Study On Seismic Vulnerability Of Mountain Highway Tunnel Considering Service Performance

The defect or lining deterioration of the operational tunnel directly affects the dynamic performance of the tunnel,which will aggravate the earthquake damage of the tunnel.Considering the outstanding engineering reality and the regional characteristics of frequent strong earthquakes in mountain tunnels in China,service tunnels with defects and damage will become the high-risk areas of future tunnel damage,seriously endanger the safety of people’s lives and property.Therefore,it is of great significance to carry out the research on the seismic damage of the operating tunnel considering the service characteristics for the realization of the total life cycle seismic performance evaluation,which has attracted extensive attention of researchers.However,the relevant researches are carried out by using the deterministic analysis method and aiming at specific conditions,which lack of considering the randomness of ground motion and the uncertainty of structure,and quantitative analysis from the perspective of probability.Based on the incremental dynamic time history analysis method and seismic vulnerability analysis theory,the seismic vulnerability of mountain tunnel under the influence of tunnel quality defects and lining degradation was carry out.The main research contents and conclusions are as follows:(1)The seismic vulnerability analysis procedures and seismic vulnerability assessment process of mountain tunnels based on IDA were described in detail.Based on the theory of vulnerability analysis,a new method to determine the maximum damage index(DI)max based on the whole process search of seismic response was proposed,which improves the shortcomings of the existing damage index value methods.In view of the large amount of post-processing data of dynamic time-history results,the programming of Python language was used to realize the automatic extraction of seismic response data.(2)A deep buried two-lane expressway tunnel in the western China was taken as an example.Considering the characteristics of the voids behind the lining,the surrounding rock conditions,the incident direction of the seismic wave and other uncertain factors such as the type and intensity of the ground motion,a series of numerical models of the tunnel seismic response were established.A large number of time history analysis of seismic response considering the interaction between tunnel and cavity was carried out.On this basis,the seismic vulnerability analysis of tunnel considering the defect of lining cavity was completed.The results show that the void size and type,surrounding rock condition have significant effects on seismic vulnerability of tunnels.The presence of voids behind the linings lead to increase the vulnerability of the tunnel,and the vulnerability presents nonlinear increase with the increment of the void size.The influence degree of void size on the vulnerability varies with the void location.Compared with the void between the primary support and the secondary lining,the tunnel containing the void between the surrounding rock and primary support is more vulnerable,so the void type cannot be ignored.The vulnerability is increased and the effects of the void on the vulnerability are more obvious when the tunnel is embedded in weak surrounding rocks.Under the same earthquake intensity,the vulnerability of normal concrete lining will be multiplied than that of reinforced concrete lining.The vulnerability under the transverse seismic direction is obviously greater than that under the vertical direction at the same seismic intensity.However,with different void location,the sensitivities of vulnerability to seismic directions are different.(3)The degradation laws of concrete and steel bar were determined by introducing the time-dependent concrete strength model and statistical characteristics of corrosion parameters of steel bar.Applying the load-bearing capacity equation of eccentric compression members and the time variable,the time-dependent load carrying capacity of tunnel lining limit state function was established.According to the theory of seismic fragility analysis,the process of seismic vulnerability assessment of mountain tunnels considering lining degradation was proposed.The seismic vulnerability curves of tunnels with different service life were obtained considering the deterioration of concrete,the corrosion of steel bar and the combined effects.The results showed that the vulnerability of the lining increased nonlinearly with the increase of service time.The damage probability of the lining increased slowly in the early stage of service(0-50 years),while increased rapidly in the late stage of service(0-50 years).The longer the service time,the effects of lining corrosion on seismic vulnerability of tunnel is the greater.Therefore,it is necessary to take into account of the deterioration of the linings for the risk assessment of the operational tunnels.In addition,the shapes of the fragility curves of tunnels with service time are similar under different surrounding rocks.Surrounding rocks and lining degradation have an important influence on the seismic vulnerability of tunnel structures.The damage probability of the tunnel increased when it is embedded in poorer quality rock mass.