Seismic Stability of Dual Tunnels in Cohesive–Frictional Soil Subjected to Surcharge Loading

Yongge Zeng,Gaoqiao Wu

doi:10.3390/app12062779

Yongge Zeng, Gaoqiao Wu

Open Access

https://doi.org/10.3390/app12062779

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Journal: Applied sciences	Publication Date: Mar 8, 2022
Citations: 1	License type: CC BY 4.0

Affiliation: Shaoyang University, Tsinghua University

Abstract

In this study, a self-developed adaptive finite element limit analysis (AFELA) code was adopted to explore the stability of dual tunnels in cohesive–frictional soil subjected to surcharge loading and seismic action. Parametric studies of different influential factors, including the depth of tunnels, horizontal distance between tunnels, seismic acceleration coefficient, unit weight, cohesion and internal friction angle of soils, were conducted using the AFELA code. An adaptive meshing technique was adopted for optimal accuracy and efficiency, and a pseudostatic method was used to simulate the seismic action. Strict upper bound (UB) and lower bound (LB) results with relative errors of less than 7% were acquired. Detailed design tables were presented to facilitate the engineering design, and three typical failure patterns, including single side-wall failure, half-cross-shaped failure and cross-shaped failure, corresponding to different stable levels, were summarized for a deeper insight into how the failure mechanism evolved under different conditions. The results indicated that the variations in soil unit weight and void depth affected the seismic bearing capacity almost linearly. Furthermore, the dual tunnel system is vulnerable to seismic actions, and the stability of tunnels was further undermined by the adverse effects of additional seismic-caused interactions between two adjacent tunnels.

Highlights

The results indicate that the solution of a single tunnel can be adopted to find double-tube solutions
The cases of double tunnels in c-φ soil without seismic action and single tunnels in c-φ soil with seismic action were compared with the previous literature [16,28] and Optum G2 [42] to verify the reliability of the present model
This study employed self-developed adaptive finite element limit analysis (AFELA) code to investigate the effect of several influential factors on the seismic bearing of double unlined parallel tunnels in cohesionfrictional soil

Summary

Introduction

With the rapid development of urbanization and highway engineering, it is difficult for road construction to avoid encountering hills, especially in the mountainous areas. Soliman et al [17] employed a finite element limit analysis (FELA) to investigate the bearing capacity of double-tube tunnels. Using upper bound FELA, Sahoo and Kumar [22] presented a series of sensitivity analyses for an insight into the bearing capacity of double tunnels in c-φ soil. They analyzed the lining pressure of dual tunnels in pure cohesion soil and c-φ soil, respectively [23]. Sahoo and Kumar [7,16] and Chakraborty and Kumar [12] combined the FELA and the pseudo-static method to investigate the seismic stability of a single tunnel under various conditions. Their investigations were verified with results from other methods, demonstrating that the FELA can effectively solve seismic stability issues

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Results

Conclusion