A Comparative Study of Protective Schemes for Shield Tunneling Adjacent to Pile Groups

Penglin Li,Jinxing Lai,Houquan Liu,Yuquan Lu,Ke Wang

doi:10.1155/2020/6964314

Abstract

Shield tunneling adjacent to pile groups is always an unavoidable problem in urban metro construction. A case was found in the project of Tianjin Metro Line 7, where a shield tunnel would be constructed near the existing pile groups of Shiyou Bridge. The whole shield tunnel is close to pile groups, and the minimum distance is only 0.8 m. Therefore, four kinds of protective schemes are proposed in this paper. It is vital to select an appropriate protective scheme to guarantee the safety during the tunnel construction. In this study, the main mechanical characteristic and physical parameters of site soil were obtained through laboratory tests. Besides, the three-dimensional finite element method was carried out to compare and analyze the effectiveness of the protective schemes in mitigating the effects of tunneling on adjacent pile groups. The results show that the deep-hole grouting scheme has better control effect on the lateral deformation and bending moment of piles, while the pile foundation underpinning scheme has better effectiveness on reducing the settlement of bridge structure and ground deformation. Finally, the deep-hole grouting reinforcement scheme will be adopted to ensure the shield passing through the pile groups smoothly.

Highlights

With the development of urban underground space, there are more and more cases of shield tunneling underneath or adjacent to existing pile foundations of buildings
In order to ensure the smooth advance of shield and the safety of adjacent pile groups, this paper makes a comparative study of the effects of protective schemes on reducing the influence of tunnel construction on pile foundations. e outline of the paper is as follows: Section 2 presents the overview of Tianjin Metro Line 7 project and describes the site geology. e main mechanical characteristic and physical parameters of site soil were obtained through laboratory tests
Shield tunneling will cause great disturbance to the surrounding soil and will have a great impact on adjacent pile groups, which will cause a certain degree of flexural deformation of pile foundation, further affecting the bearing capacity of pile foundation. erefore, in order to ensure the safety of pile structure, it is essential to take some measures, among which shield construction parameters should be optimized first

Summary

Introduction

With the development of urban underground space, there are more and more cases of shield tunneling underneath or adjacent to existing pile foundations of buildings. Fu et al [45] evaluated the effectiveness of underground jet-grouted partition wall in mitigating the effects of shield-tunnel construction on existing piled structures through numerical analysis and field monitoring. Ey analyzed monitoring data before and after the shield body crossing the bridge and found that these enhancements can effectively decrease bridge settlement during tunneling and improve mechanical conditions of bridge structures In such a difficult engineering background, the previous researches on this aspect are still not rich enough. In order to ensure the smooth advance of shield and the safety of adjacent pile groups, this paper makes a comparative study of the effects of protective schemes on reducing the influence of tunnel construction on pile foundations. Conclusions and sum-up of the paper are presented

Engineering Background

Numerical Simulation

Selection of Protective Schemes

Findings

Comparative Analysis of Protective Schemes