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Geomechanics and Engineering
  Volume 15, Number 5, August10 2018 , pages 1039-1046

Limit analysis of a shallow subway tunnel with staged construction
Shengbing Yu

    This paper presents a limit analysis of the series of construction stages of shallow tunneling method by investigating their respective safety factors and failure mechanisms. A case study for one particular cross-section of Beijing Subway Line 7 is undertaken, with a focus on the effects of multiple soil layers and construction sequencing of dual tunnels. Results show that using the step-excavation technique can render a higher safety factor for the excavation of a tunnel compared to the entire cross-section being excavated all at once. The failure mechanisms for each different construction stage are discussed and corresponding key locations are suggested to monitor the safety during tunneling. Simultaneous excavation of dual tunnels in the same cross-section should be expressly avoided considering their potential negative interactions. The normal and shear forces as well as bending moment of the primary lining and locking anchor pipe are found to reach their maximum value at Stage 6, before closure of the primary lining. Designing these struts should consider the effects of different construction stages of shallow tunneling method.
Key Words
    limit analysis; strength reduction; shallow tunneling method; stability
Shengbing Yu: 1.) School of Civil Engineering and Water Conservancy, Ningxia University, Yinchuan 750021, China
2.) Engineering Research Center of Efficient Use of Water Resources in Arid Modern Agriculture, Ministry of Education,
Yinchuan 750021, China
3.) Ningxia Irrigation and Water Resources Control Engineering Technology Research Center, Yinchuan 750021, China

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