Dynamic centrifuge tests on isolation mechanism of tunnels subjected to seismic shaking |
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| Affiliation: | 1. Department of Geotechnical Engineering, Tongji University, Shanghai 200092, PR China;2. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Shanghai 200092, PR China;1. Aristotle University of Thessaloniki, Research Unit of Soil Dynamics and Geotechnical Earthquake Engineering, Department of Civil Engineering, PO Box 424, GR-54124 Thessaloniki, Greece;2. University of Catania, Department of Civil and Environmental Engineering, Sicily, Italy;1. School of Civil Engineering, Dalian University of Technology, Dalian, PR China;2. Institute of Mountain Hazards and Environment, Chinese Academy of Science, Chengdu, PR China;3. Design and Research Institute, Sichuan Provincial Transportation Department, Chengdu, PR China;4. School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang, PR China;1. Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China;2. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092, China;3. Lyles School of Civil Engineering, Purdue University, West Lafayette, IN 47906, USA;4. State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China;1. State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and the Ministry of Science and Technology, Shandong University of Science and Technology, Qingdao 266590, China;2. School of Engineering, Nagasaki University, 1-14 Bunkyo-machi, 852-8521 Nagasaki, Japan |
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| Abstract: | Isolation layer is one of the countermeasures to enhance seismic safety of tunnels. Its behavior under earthquake is affected by many factors such as shape of the tunnel, stiffness of the isolation layer and the characteristics of the input motion. However, current knowledge on the effects of these parameters on the seismic behavior of isolation layer is limited to lack of experimental data. This paper focuses on the mechanism of isolation layer, especially the efficacy of input motion frequencies on the seismic behavior of a square tunnel with isolation layer around its outer surface. Dynamic centrifuge tests were carried out on model tunnels which took isolation layer as seismic countermeasure using input motion of sinusoidal waves of different frequencies. Actual records of ground motions, magnified to approximate 15 g peak acceleration, formed the basis of the excitations to verify the actual efficacy. Due to the difference between model material (aluminum alloy) and prototype material (concrete), the similar flexural deformation law and the similar axial deformation law could not be satisfied simultaneously. Given the fact that cross-sectional moments were one of the main factors that influenced the safety of tunnels under dynamic loadings, the similar flexural deformation law was accepted in model preparation. The results show that the bending strains of tunnel with isolation layer around its outer surface are lower than those of tunnel without isolation layer, which indicates that isolation layer has positive effect on moment reduction, especially at corners. Increasing of the input motion frequency decreases the dynamic cross-sectional bending moments. In addition, isolation layer has little influence on frequency contents of acceleration response of tunnel. This study has clarified the mechanism of isolation layer on shock absorption, which is proved to be an effective method to improve the safety of tunnel against earthquake. |
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| Keywords: | Tunnel Isolation layer Seismic reduction Dynamic centrifuge test Frequency of input motion |
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