Convergence deformation monitoring of a shield tunnel based on flexible long-gauge FBG sensors

Abstract

For subway safety, it is important to monitor the convergence deformation of shield tunnels in the long term. However, traditional monitoring methods are constrained by high cost and technical difficulties. Herein, improvements achieved through use of a new type of optical fiber (OF) sensor are reported. The new type of optical fiber sensor, namely, the flexible long-gauge Fiber Bragg Grating (FBG) sensor, is proposed with descriptions of design, preparation and strain sensing performance. Then, a method of assessing convergence deformation is proposed based on distributed long-gauge strain measurements. Finally, the proposed method is validated with measurements made on two full size specimens of shield segments. It is also concluded that the seam change shows a strong influence on convergence deformation. From static experiments, convergence deformation can be accurately evaluated to satisfy the demands of tunnel management. Considering the additional advantages of distributed sensing, such as sensing distance, stability and durability, the proposed method exhibits broad application prospects.

Keywords:

• Shield tunnel
• flexible long-gauge sensor
• distributed strain sensing
• fiber Bragg grating sensor
• convergence deformation monitoring

Acknowledgments

The authors are grateful for the financial support provided by the Provincial special fund project of strategic emerging industry development in Jiangsu Province (Grant No. 2020645).

Declaration of interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.