Geomechanics and Engineering

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Investigations of countermeasures used to mitigate tunnel deformations due to adjacent basement excavation in soft clays

  • Jinhuo Zheng (Fujian Provincial Institute of Architectural Design And Research Co.,Ltd.) ;
  • Minglong Shen (Fujian Provincial Institute of Architectural Design And Research Co.,Ltd.) ;
  • Shifang Tu (China Railway 16th Bureau Group 3rd Corporation Limited) ;
  • Zhibo Chen (Department of Geotechnical and Geological Engineering, Zijin School of Geology and Mining, Fuzhou University) ;
  • Xiaodong Ni (Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Hohai University)
  • Received : 2023.11.27
  • Accepted : 2024.02.27
  • Published : 2024.03.25
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Abstract

In this study, various countermeasures used to mitigate tunnel deformations due to nearby multi-propped basement excavation in soft clay are explored by three-dimensional numerical analyses. Field measurements are used to calibrate the numerical model and model parameters. Since concrete slabs can constrain soil and retaining wall movements, tunnel movements reach the maximum value when soils are excavated to the formation level of basement. Deformation shapes of an existing tunnel due to adjacent basement excavation are greatly affected by relative position between tunnel and basement. When the tunnel is located above or far below the formation level of basement, it elongates downward-toward or upward-toward the basement, respectively. It is found that tunnel movements concentrate in a triangular zone with a width of 2 He (i.e., final excavation depth) and a depth of 1 D (i.e., tunnel diameter) above or 1 D below the formation level of basement. By increasing retaining wall thickness from 0.4 m to 0.9 m, tunnel movements decrease by up to 56.7%. Moreover, tunnel movements are reduced by up to 80.7% and 61.3%, respectively, when the entire depth and width of soil within basement are reinforced. Installation of isolation wall can greatly reduce tunnel movements due to adjacent basement excavation, especially for tunnel with a shallow burial depth. The effectiveness of isolation wall to reduce tunnel movement is negligible unless the wall reaches the level of tunnel invert.

Keywords

Acknowledgement

This work described in this paper is supported by a research grant from Housing and Urban-rural Development of Fujian, China (Grant No. 2022-K-330), and National Natural Science Foundation of China (Grant No. 52278335).

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