Excavation Face Stability of Shield Tunneling Closely Under Existing Tunnels: Particle Flow Simulation
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RESEARCH PAPER
Excavation Face Stability of Shield Tunneling Closely Under Existing Tunnels: Particle Flow Simulation Fei Xue1 · Mengxi Zhang1 Received: 18 June 2019 / Accepted: 20 February 2020 © Shiraz University 2020
Abstract When a new tunnel passes closely under an existing tunnel, it will induce ground subsidence and adversely affect the existing subway tunnel. Aiming at the construction form of shield passing closely under existing tunnel, a numerical model using twodimensional particle flow was set up to study the failure form of the excavation face, the relationship between support force and excavation displacement, longitudinal deformation of the surface and the earth pressure distribution pattern around the existing tunnel. The results show that the support pressure of shield excavation face increases first and then decreases with the increase in excavation surface displacement due to the presence of existing tunnel. The maximum vertical settlement value of the ground surface appears in the range of 2D from the center of the existing tunnel. With the advance of shield tunnel, the earth pressure above the new tunnel segment increases gently. When away from the existing tunnel, the horizontal earth pressure above the tunnel increases gradually, and the earth pressure in the area ahead of the shield tunnel along the depth presents a significant nonlinear distribution. The research results can provide theoretical basis and early guidance for such construction in the future. Keywords Shield tunnel · Short-distance construction · Excavation face stability · Particle flow code simulation · Earth pressure distribution model List of Symbols kn Normal stiffness ks Tangential stiffness f Friction coefficient Z Distance between excavation face of new shield tunnel and center of existing tunnel D Diameter of new shield tunnel and existing tunnel
1 Introduction With the rapid development of cities, urban rail transit has entered the stage of high-speed construction. According to the plan, by 2020, 89 new rail transit lines will be built in China, with a total construction mileage of 2500 km and a total investment of 623.5 billion Chinese Yuan. Shanghai alone will have 22 lines, with a mileage exceeding 1000 km (Ma et al. 2016). Because of the increase in mileage and * Fei Xue [email protected] 1
Department of Civil Engineering, Shanghai University, Shanghai 200444, China
the convenience of people transferring from one station to another, there are many engineering examples of new tunnels crossing existing tunnels (Li et al. 2014; Xiao et al. 2011). When several subway lines intersect, the deformation mechanism of the surface and existing tunnel becomes very complex when the new shield tunnel is excavated in the overlapping section. In the overlapping area of shield tunnel, the construction of new tunnels has a complex impact on the surrounding environment, especially on existing tunnels, which will lead to cracking and leakage of existing tunnels, affect the normal use of tunnels and even pose a serious
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