Large-scale shaking table test for vibration-absorption measures of portal section of huangcaoping tunnel No.2

In order to study the effects of vibration-absorption measures in mountainous tunnel during earthquake, the entry portal area of Huangcaoping Tunnel No.2 located on National Highway No.318 is selected as the prototype to conduct large-scale shaking table test. Firstly, the whole test scheme is systematically introduced, including the test facility, the design of similarity ratio, the design of mould case, the similarity materials, the layout of measure sensors, the wave input and the load subsequence. Then, combining the test result analysis, the sector of the portal area that needs seismic protection is researched; and the effects of vibration-absorption measures such as lateral buffer layer, longitudinal buffer layer, and reinforcing surrounding rock with systematic bolts are analyzed. The results show that from the entry to the deep locations, the earthquake-induced effect decreases step by step, and gets stable at the distance of 120-150 cm in model (48-60 m in prototype), which can be considered as the most important zone for aseismic design. The results also show that setting lateral buffer layer and reinforcing surrounding rock with bolts are both effective ways to decrease the dynamic earth pressure and the liner acceleration; but the latter is relatively weaker than the former. Properly setting longitudinal buffer layer can effectively reduce the dynamic strain to an acceptable level for project safety. Finally, the some suggestions are put forward that synthetical measures for vibration-absorption should be adopted for aseismic safety design of mountainous tunnel portal area on the basis of the above results.