Failure Mechanism of Face for Slurry Shield-Driven Tunnel in Sand
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pISSN 1226-7988, eISSN 1976-3808 www.springer.com/12205
DOI 10.1007/s12205-020-1448-5
Tunnel Engineering
Failure Mechanism of Face for Slurry Shield-Driven Tunnel in Sand Handong Liua, Yafeng Zhanga, and Haining Liua a
Henan Key Laboratory of Geotechnical and Structural Engineering, North China University of Water Resources and Electric Power, Zhengzhou 450046, China
ARTICLE HISTORY
ABSTRACT
Received 23 August 2019 Revised 1st 15 February 2020 Revised 2nd 23 April 2020 Accepted 29 May 2020 Published Online 14 August 2020
To achieve the failure mechanism of face for slurry shield tunnel in sand stratum, a model test device for shield excavation with ideal slurry film was developed. The active failure processes of tunnel excavation face in dry sand stratum for different densities and cover depths were achieved through model test and two-dimensional particle flow code (PFC2D). Furthermore, soil deformation, failure mode and soil arching effect of tunnel excavation face were revealed. The results show that the face deformation can be divided into three stages in relation to the support pressure and the excavation face has been failed in third stage. The density of sand has a great influence on the failure mode of excavation face. The failure mode in dense condition is a combination of a wedge with slip arc and a prism chimney, while in loose condition it is a relatively dispersed “trumpet” shape failure zone. However, the cover depth has a negligible effect on the failure mode. In dense sand stratum, a loose failure zone was formed in front of the excavation face and a soil arch was formed above it. The soil arch developed continuously above the tunnel crown to the ground surface. The limit support pressure calculated by PFC2D (two-dimensional particle flow code) increases with the cover depth, which is consistent with the observations in model tests.
KEYWORDS Slurry shield tunneling Excavation face stability Model test PFC2D Soil arching effect Limit support pressure
1. Introduction In recent years, because of its better adaptability to complex strata and high ground water level compared with other tunnel construction methods, slurry shield tunneling have been widely used for urban subway tunnels, cross-river tunnels, and subsea tunnels, especially in sand or sand-pebble strata, e.g., the Shanghai Yangtze River Cross-river Tunnel (Wang, 2008) and the Nanjing Yangtze River Cross-river Tunnel (Min et al., 2015). In the process of slurry shield tunneling, slurry infiltrates into stratum, when an impervious or slightly permeable film was formed (Broere and van Tol, 2000). Slurry film can not only prevent the groundwater, but also transform slurry pressure into support pressure, so as to balance the earth and water pressure in front of the excavation face (Anagnostou and Kovári, 1994; Min et al., 2013). Too low slurry pressure would lead to the failure of excavation face, which would not only cause surface settlement and collapse, but affect the surrounding buildings, structures and pipeline rupture. Therefore, h
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