Working mechanism of cutoff walls in reducing uplift of large underground structures induced by soil liquefaction |
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| Institution: | 1. Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, USA;2. Department of Civil and Environmental Engineering, University of California, Davis, USA;1. School of Civil Engineering, State Key Laboratory of Hydroscience and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing, China;2. School of Civil Engineering, State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China;3. Ertan Hydropower Development Company Limited, Chengdu 610051, China;1. Institute of Geotechnical Engineering, Nanjing Tech University, Nanjing 210009, China;2. Civil Engineering and Earthquake Disaster Prevention Center of Jiangsu Province, Nanjing 210009, China;3. College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100022, China;4. School of Civil and Transportation Engineering, Beijing University of Civil Engineering and Architecture, Beijing 100044, China;1. Key Laboratory of Urban Security and Disaster Engineering of Ministry of Education, Beijing University of Technology, Beijing 100124, China;2. China Academy of Railway Sciences Corporation Limited, Urban Rail Transit Center of CARS, Beijing 100081, China;1. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China;2. School of Civil Engineering and Architecture, East China Jiaotong University, Nanchang 330013, China;3. Institute of Geotechnical Engineering, Nanjing Tech University, Nanjing 210009, China;4. College of Civil Engineering, Beijing University of Technology, Beijing 100124, China;1. Key Lab of Structures Dynamic Behavior and Control, Harbin Institute of Technology, Ministry of Education, Harbin, Heilongjiang 150090, China;2. School of Civil Engineering, Harbin Institute of Technology, Harbin, Heilongjiang 150090, China |
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| Abstract: | The uplift of large underground structures in saturated liquefiable soils under strong earthquake loadings may induce severe damages to the structures. Various mitigation procedures have been proposed to alleviate such damage, among which installation of cutoff walls next to underground structures was found to be effective. However, the working mechanism of cutoff walls in alleviating uplift of underground structures and the corresponding design parameters are still not clear. The liquefaction induced uplift behaviour of a subway tunnel in saturated sandy deposit over a layer of non-liquefiable soils and the working mechanism of cutoff walls for uplift mitigation purpose were investigated using the fully coupled dynamic finite element code DIANA Swandyne-II. A generalized plasticity model capable of simulating both cyclic liquefaction and pressure dependency of soils was used to model the sandy deposit. It is found that the small effective unit weight of underground structures, the development of excess pore pressure and the flow of liquefied soils were the sufficient and necessary conditions for underground structures to uplift during earthquakes. Cutoff walls could restrain the flow or deformation of liquefied soils and inhibit the uplift of underground structures but they could not necessarily prevent the liquefaction of the enclosed soils. After earthquake loadings, underground structures might settle due to the consolidation of soils and cutoff walls could also reduce the magnitude of settlement. The design parameters of cutoff walls, including the acting lateral pressure, the position, the stiffness and the permeability of cutoff walls, were also analyzed, the findings of which, together with the unveiled working mechanism, would be relevant for the design of cutoff walls for uplift mitigation purpose. |
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