Sismic Fragility Analysis Of Rock Tunnel Based On Improved Response Surface Method

Reasonable seismic vulnerability model is the foundation of seismic fortification of tunnel structures.Ground motion and site conditions have great uncertainty,which is difficult to be fully considered in vulnerability analysis.The present tunnel seismic vulnerability curve is mostly obtained by selecting representative ground motion data and site condition analysis,but it cannot accurately predict the damage status of specific tunnel structures in future earthquakes.Therefore,it is necessary to study the seismic vulnerability of tunnels more carefully to establish a universal earthquake vulnerability model.In this study,conditional failure probability of the rock tunnels under various states is calculated based on an improved response surface method.Then the lining damage prediction model was set up and be used to construct seismic vulnerability curve of the lining and the tunnel connecting system,which provides strategic support for tunnel reliability assessment and post-earthquake emergency rescue.The main contents of this paper include the following aspects:(1)To reduce the number of deterministic seismic response analysis required in calculating the conditional failure probability of tunnels,the existing methods were improved and an improved response surface method based on sampling optimization is proposed,and its accuracy and efficiency were verified by two numerical examples.The new method then was applied to construct lining damage prediction model.(2)The parametric modeling methodology was proposed for the lining and surrounding rock based on Matlab and Abaqus.25 working conditions were generated by Box-Behnken design.At each working condition,the improved response surface method was used to solve the conditional failure probability of lining corresponding to different failure states,and the damage prediction model between four design parameters(free field maximum shear strain,surrounding rock elastic modulus,tunnel radius and lining thickness)and the failure probability was established.Then taking a specific tunnel as an example,the maximum shear strain of free field under different ground motion intensity measure was calculated by equivalent linear analysis,and the seismic vulnerability curve was obtained by substituting the damage prediction model.(3)The connectivity of tunnel system was defined and the seismic connectivity vulnerability analysis method was given based on the vulnerability analysis of tunnel lining.Four tunnel systems are taken as examples to analyze the influence of tunnel system size on tunnel connectivity reliability.