Assessment of the Stability of an Unlined Rectangular Tunnel with an Overload on the Ground Surface

Jian Zhang,Zhibin Hang,Feng Yang,Tugen Feng,Ma Jianjun

doi:10.1155/2020/6616067

Jian Zhang, Zhibin Hang + Show 3 more

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https://doi.org/10.1155/2020/6616067

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Abstract

City tunnels are often constructed at shallow depths, and tunnel failure may be initiated by overloads resulting from surrounding buildings, structures, heavy-haul trailers, and other installations. Although several works have been reported on tunnel stability, stability numbers have mainly been obtained for cases with fully cohesive soils. Moreover, little information has been presented about the influence of overloads on the failure patterns for unlined rectangular tunnels. This paper uses upper-bound finite element methods to assess the stability of an unlined rectangular tunnel in cohesive-frictional soils with an overload acting on the ground surface. A complete set of dimensionless parameters covering the tunnel size and shallow tunnel depth and Mohr-Coulomb material parameters are determined to obtain the dimensionless overload. In addition, failure modes that are similar to slip line fields are acquired. A failure mechanism that may cause base heave is proposed in this paper to improve the accuracy of the results. These failure patterns are more complex for cases with larger dimensionless depth, larger internal friction angle, and smaller dimensionless unit weight. Compared with the rigid-block mechanisms from the upper-bound rigid-block analysis method, these computed failure mechanisms are better suited for rectangular tunnel stability analysis.

Highlights

Due to the rapidly increasing demand for urban construction and the improvement in social welfare, tunnels have been widely constructed in underground engineering applications, such as subways, electric utilities, and city infrastructure. ese tunnels are often constructed at shallow depths, and tunnel failures may be initiated by overloads resulting from surrounding buildings, structures, heavyhaul trailers, and other installations
Rectangular tunnels have a higher degree of utilization of underground space and a lower volume of earthwork excavation; a rectangular tunnel is often a valid option due to the development of advanced tunneling machines
Several works have been reported on rectangular tunnel stability, stability numbers have mainly been obtained for cases with fully cohesive soils

Summary

Introduction

Due to the rapidly increasing demand for urban construction and the improvement in social welfare, tunnels have been widely constructed in underground engineering applications, such as subways, electric utilities, and city infrastructure. ese tunnels are often constructed at shallow depths, and tunnel failures may be initiated by overloads resulting from surrounding buildings, structures, heavyhaul trailers, and other installations. For cohesive-frictional soils, Yamamoto et al [40, 41] determined square tunnel stability with an overload on the ground surface using UBFEM and LBFEM; in these studies, they determined the ultimate overloads and presented an empirical equation for approximating the ultimate overload.

Results

Conclusion