Study On Seismic Design Optimization In Xiaoshicun Long Tunnel Of Wuguan Highway

As the strongest earthquake recent years, the Wenchuan Earthquake (M8.0) on May12nd,2008, has caused very severe casualties and property losses. The geological hazards such as the rock avalanche, rockfall, landslides, ground fissures and secondary debris flow triggered by the Earthquake led to the lining cracking of tunnels and blockage of portals, which badly influenced the quick and timely rescue work after earthquake. Therefore, a new subject and higher seismic technical requirements have been demanded to solve the seismic safety of tunnels located at the highly seismic areas.Based on the background of the project of earthquake-resistant technique and the optimization of mountain tunnels along the Wuguan Expressway, the portal segment of the Xiaoshicun Tunnel was studied as an example from the following aspects:1. On the basis of the extensive collection of tunnels earthquake hazard cases both at home and abroad, especially the newest research data of tunnel structure deformations and failures in the Wenchuan Earthquake and historical earthquakes, the failure modes, main influence factors, earthquake hazards characteristics and failure mechanism of mountain tunnels were throughly analyzed and summarized by classification statistics and induction. Then the earthquake-resistant experiences and enlightments of mountain tunnels were suggested.2The engineering geological conditions and ground motion parameters of Xiaoshicun Tunnel were analyzed. The element mesh discretization, constitutive equations of materials and dynamical boundary conditions were discussed during establishing of numerical simulation model. Then the key calculation parapters needed for dynamic response analysis on the Xiaoshicun Tunnel were determined.3Relying on the left line tunnel portal segment of the Xiaoshicun Tunnel, the dynamic response analysis were conducted by MIDAS/GTS. The response patterns of stress, displacement and acceleration of the tunnel structure were respectively studied both under the single horizontal earthquake action and the interaction of horizontal and vertical earthquake actions. The results indicated that the difference of seismic response in diffrent parts of tunnel linging was significant, the responses under both horizontal and vertical earthquake action was bigger than that under single horizontal motion. Therefore the seismic response under bi-direction motion should be considered.4Based on the summarization and induction of the earthquake-risistant researches on tunnel structures both at home and abroad, the method of surrounding rock grouting reinforcement was selected to study the earthquake-resisitant effect, where the grouting depth were3m,4.5m and6m respectiviely. The response patterns of stress, displacement and acceleration of the tunnel structure were obtained. The optimum depth of grouting should be5m from the simulation results. Finally, the study and results were summarized, and the limitations of this research and the future research directions were pointed out.