Highway Tunnel Seismic Optimization Numerical Simulation Analysis

As the strongest earthquake recent years，the Wenchuan Earthquake (M8.0)on May12nd,2008，has caused very severe casualties and property losses. Thegeological hazards such as the rock avalanche, rockfall, landslides, groundfissures and secondary debris flow triggered by the Earthquake led to the liningcracking of tunnels and blockage of portas, which badly influenced the quickand timely rescue work. Therefore, a new subject and higher seismic technicalrequirements have been put forward to solve the seismic safety of tunnelslocated at the highly seismic areas.Based on the background of the project of earthquake-resistant techniqueand the optimization of mountain tunnels along the Wuguan Expressway, theportal segment of the Xiaoshicun Tunnel was studied as an example from thefollowing aspects:1. On the basis of the extensive collection of tunnels earthquake hazardcases both at home and abroad, especially the newest research data of tunnelstructure deformations and failures in the Wenchuan Earthquake and historical earthquakes, the failure modes, main influence factors, earthquake hazardscharacteristics and failure mechanism of mountain tunnels were throughlyanalyzed and summarized by classification statistics and induction. Then theearthquake-resistant experiences and enlightments of mountain tunnels weregiven.2. The engineering geological conditions and earthquake motion parametersof Xiaoshicun Tunnel were analyzed. The element mesh division, constitutiveequations of materials and dynamical boundary conditions were discussedduring establishing of numerical simulation model. Then the key calculationparapters needed for dynamic response analysis on the Xiaoshicun Tunnel weredetermined3. Relying on the portal segment of the Xiaoshicun Tunnel, the dynamicresponse analysis were conducted by MIDAS/GTS. The response patterns ofstress, displacement and acceleration of the tunnel structure were respectivelystudied both under the single horizontal earthquake action, the longitudinalearthquake action and the historical earthquakes. The results indicated that the tunnel lining structure in different parts of the earthquake response has a biggerdifference, different direction to vibration on the tunnel lining of the influence ofthe obvious difference, so it should be considered in vibration incident direction4. Based on the summarization and induction of the earthquake-risistantresearches on tunnel structures both at home and abroad, the method ofsurrounding rock grouting reinforcement was selected to study theearthquake-resisitant effect, where the grouting depth were3m,6m and8mrespectiviely. The response patterns of stress, displacement and acceleration ofthe tunnel structure were obtained. The optimum depth of grouting should be6mfrom the simulation results.