Mechanism and countermeasures of preceding tunnel distortion induced by succeeding EPBS tunnelling in close proximity |
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| Institution: | 1. School of Civil Engineering, Tianjin University, Tianjin 300072, China;2. Key Laboratory of Coast Civil Structure Safety (Tianjin University), Ministry of Education, China;3. State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin 300072, China;1. Ruhr-Universität Bochum, Faculty of Civil and Environmental Engineering, Chair of Computing in Engineering, 150, Universitätsstr., 44780 Bochum, Germany;2. Ruhr-Universität Bochum, Faculty of Civil and Environmental Engineering, Chair for Foundation Engineering, Soil and Rock Mechanics, 150, Universitätsstr., 44780 Bochum, Germany;1. Key Laboratory of Geotechnical & Underground Engineering of Ministry of Education, Department of Geotechnical Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China;2. Shanghai Jianke Project Management Co., Ltd., 75 Wanping South Road, Shanghai 200032, China;1. Institute of Tunnel and Underground Structure Engineering, School of Civil Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China;2. School of Civil Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China;3. School of Highway, Chang’an University, Xi’an 710064, China;1. School of Civil Engineering, Tianjin University, Tianjin 300072, China;2. 5th Engineering Co Ltd, China Railway 18th Bureau, Tianjin 300451, China |
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| Abstract: | Twin tunnels are frequently used to address the increasing transportation demands in large cities. To ensure the safety of twin tunnels in close proximity, it is often necessary to take protective measures that have not been well studied. Field monitoring was conducted for a project of twin earth pressure balance shield (EPBS) tunnels in typical soft ground. The preceding tunnel was reinforced by various measures, including trailer bracing, compensation grouting, artificial freezing and scaffold bracing. The entire deformation of the reinforced tunnel was recorded during the succeeding tunnelling process. A three dimensional finite-element method (FEM) model was established to simulate the entire process of twin EPBS tunnelling, particularly the reinforcement measures. The computed deformations of the reinforced tunnel were consistent with the measured data. Furthermore, the stress history and pore pressure of the surrounding soil were analysed to investigate the deformation mechanism of the tunnel. Both the measured and computed results indicate that although the face pressure of the succeeding tunnel was smaller than the earth pressure at rest, the preceding tunnel could still experience an inward horizontal convergence and a deflection away from the succeeding tunnel. These distortion modes were caused by the squeezing effect of the horizontal soil arch in front of the succeeding tunnel face. Finally, convergence and deflection indices were proposed to quantify and assess the effectiveness of the reinforcement measures. The trailer bracing, as an “in-tunnel” reinforcement technique, was found to be the most effective method for controlling tunnel convergence. However, artificial freezing as an “out-tunnel” reinforcement technique led to the largest reductions in tunnel deflection. A combination of both “in-tunnel” and “out-tunnel” reinforcements was recommended. |
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| Keywords: | Twin tunnels Field monitoring Three dimensional FEM model Preceding tunnel deformation Horizontal soil arch Reinforcement measures |
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