Undrained Stability Analysis of Shallow Tunnel and Sinkhole in Soft Clay: The Cavity Contraction Method

Hui Qi,Gongzeng Yang,Xiaonan Wang,Hongya Yue,Huaijian Li,Junwei Cheng,Wenjie Cui,Jianliang Zhang,Lingdi Kong,Xiuguang Song

doi:10.3390/app11199059

Abstract

This paper presents theoretical methods for the undrained stability analysis of shallow tunnels/sinkholes in clay based on the cavity contraction theory, with some assumptions and simplifications. To examine the accuracy and reliability of the new methods, a database was assembled, which consists of stability numbers of tunnel/sinkholes in clays from 22 centrifuge model tests, 10 field tests, and 62 FELA results. It is shown that the proposed methods give an average of 2.5% overestimation for the stability numbers from model tests and is in a good agreement with the FELA results. The cavity contraction theory-based methods are then discussed, which could provide useful guidance for designers to roughly assess shallow tunnel/sinkhole stability in clays.

Highlights

Ground stability is one of the two major concerns for geotechnical engineering practices, which require that the ground soil mass remains stable under the given or expected loading conditions
Many studies have investigated the undrained stability of shallow tunnels and sinkholes by model tests [5,6], the limit analysis method [1,7,8,9,10,11,12,13,14,15], and the displacement finite element/difference method [16,17]
To investigate the influence of embedment ratio and tunnel heading geometry on tunnel stability, Mair [5] conducted two series of 2D/3D centrifuge model tests in clays, and found that the tunnel heading stability was strongly affected by the tunnel heading geometry

Summary

Introduction

Ground stability is one of the two major concerns for geotechnical engineering practices, which require that the ground soil mass remains stable under the given or expected loading conditions. For tunnel stability in undrained clay, Yu [25] proposed a simple equation based on cavity contraction theory in Tresca materials. This equation failed to consider the influence of finite cover depth on tunnel stability, which could overestimate the stability for a shallow tunnel. There is no equation, to the best knowledge of the authors, that can be directly used to account for the stability of a tunnel heading To fill these gaps, this paper mainly extends the work of Yu [25] and modifies Yu’s equation by developing the cavity contraction theory in a finite Tresca soil mass. A simple equation that could predict the tunnel/sinkhole stability is proposed based on the newly developed cavity contraction solution, and validated after comparison with published results

Problem Definition

Validation and Discussion

D Tunnel Stability Analysis

Methods