Tunnel face failure mechanism with sand layer partial collapse
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ORIGINAL PAPER
Tunnel face failure mechanism with sand layer partial collapse Zhuo Zheng 1 & Rentai Liu 1 & Shucai Li 1 & Qingsong Zhang 1 Received: 9 August 2018 / Accepted: 2 October 2020 # Saudi Society for Geosciences 2020
Abstract In this paper, a DEM model is proposed based on Particle Flow Codes (PFC) software, which simulates a sand layer collapse process in tunnel excavation of Qingdao subway project. The fluid–particle interaction was solved with the coarse-grid method in order to account for the influence of groundwater on the movement of sand layer. The development of sand layer collapse and the displacement field were acquired, and the variation of porosity and stress were calculated. Influencing rules of mechanical property of sand layer on the stability were revealed. The maximum settlement occurred at the arch crown of the tunnel, and it reduced gradually up to the ground surface. The porosity and sand inflow amount have a positive relation, while the vertical stress with the sand inflow amount has a negative relation. The influence of silty clay on the stability of the tunnel face was also investigated. For the condition with 2% silty clay amount, the inflow amount reached almost 300 m3 after 1 day, while for the condition with 20% silty clay amount, the inflow amount was only 25 m3, which is regarded as stable during excavation. Key words Tunnel excavation . Face stability . Discrete element method . Solid–fluid interaction
Introduction Tunnel face stability and ground surface settlement due to tunnel excavation are two important factors in the design of shallow tunnels. In many cases, the self-stability of the stratum is not sufficient to balance the external earth and water pressure. As a result, the tunnel face may become unstable or collapse. On the other hand, the tunnel displacements should be limited within tolerable deformations thresholds in case it propagates to the surface and make an impact on existing structure. Thus, it is important to control the stability of tunnel face displacement during excavation for guaranteeing safety during tunnel construction. The problem of tunnel face stability was first studied theoretically by pioneering researchers. This theoretical analysis includes limit equilibrium methods and limit analysis methods (upper and lower bound plastic theory). For limit equilibrium methods, Horn (1961) proposed a primitive three-dimensional model to analyze the tunnel face failure. The failure zone is Responsible Editor: Zeynal Abiddin Erguler * Zhuo Zheng [email protected] 1
Geotechnical and Structural Engineering Research Center, Shandong University, No.17923, Jingshi Road, Jinan 250061, Shandong, China
predefined as to be wedge-shape, which is loaded by a soil silo. Krause (1987) investigated the influence of different shapes of the failure zone, such as half sphere, half circle, and quarter circle. The limit support pressure for each condition was calculated. Anagnostou and Kovári (1996) used the wedge model to investigate the stability of tunnel face with earth
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