Segment Stress Characteristics and Ground Deformation Caused by Constructing Closely Spaced Parallel Tunnels under a Complex Geological Condition

Jianbing Lv,Xulong Li,Helin Fu,Zhanrong Li,Bing Fu,Xiaodong Xie,Hui Zhao,Yong Tang,Zikun Li,Chunshun Zhang

doi:10.1155/2020/1725210

Abstract

Ground deformation and additional stress on the segments of the firstly constructed tunnel may change significantly due to the construction of another tunnel, which is closely spaced with the existing one. A poor geotechnical condition possibly leads to the interaction between such closely spaced tunnels even making it harder to build such tunnels. A practical project located in Guangzhou City, China, consists of such two parallel tunnels with the smallest distance of 2.6 m, which sat on an upper-soft and lower-hard stratum. A 3D finite element model has been proposed to numerically investigate the behavior of these two parallel tunnels. The numerical results predicted by the FE model are in close agreement with that obtained from the field monitoring system, indicating the accuracy of the proposed FE model. The FE model was then used to further analyze the effect of reinforcing piles in eliminating the detrimental effect on both ground deformation and additional stress of the segments of the existing tunnel as a result of the construction of the new parallel tunnel. The research results obtained from the present paper can provide technical support and guidance for urban subway construction.

Highlights

In recent years, the scale of urban underground space development and utilization has been expanding at a fast rate [1], and more and more means have been used to study underground space [2,3,4]
In order to enhance the understanding of the interaction between two parallel tunnels, a number of investigations have been conducted including theoretical analysis, numerical simulation, model test, and construction monitoring [10,11,12,13,14]
Fu et al [15] studied the ground deformation caused by the excavation of double parallel tunnels, in which complex variable theory was employed. e results showed that the superposition principle can be used to determine the ground deformation caused by constructing two closely spaced parallel tunnels

Summary

Introduction

The scale of urban underground space development and utilization has been expanding at a fast rate [1], and more and more means have been used to study underground space [2,3,4]. Parallel shield tunnels with a small space have been often encountered when constructing urban metros in China [5,6,7] In such a case, the interaction between the two parallel tunnels becomes significant, leading to the large deformation of surrounding rock and a complex stress state of segments of the lining structure. Zhang et al [17] used the limit analysis of nonlinear failure criterion and reliability theory to obtain the effect of the clear spacing on the safety levels of the closely spaced parallel tunnels, which provided a theoretical basis to ensure the safety for excavating such closely spaced parallel tunnels Fang and He [18] concluded that the bending moment of each section in the segment ring of the existing tunnel decreases while the axial force increases due to the construction of the later tunnel, which is parallel to the existing one with a small distance. E effect of isolation piles on construction safety has been analyzed using the proposed FE model as well

Description of the Practical Cases

Numerical Investigation

Verification of the Proposed FE Model Using Field Monitoring Results