Research on Circumferential Deformation of Metro Shield Tunnel Based on FBG Monitoring Technology

Abstract

Objective FBG (fiber bragg grating) monitoring technology features fast dynamic response, strong anti-interference, high precision and strong durability, and can realize long-distance real-time monitoring. The feedback circumferential deformation monitoring data from FBG is of great significance to the parameter adjustment in the process of shield tunneling. Therefore, it is necessary to conduct an in-depth research on the circumferential deformation law of the segments based on FBG technology. Method With a metro tunnel project as the example, the fiber optic sensors are used for real-time monitoring of the segments during metro tunnel construction. Through analysis of the monitoring data, the changing law of the circumferential strain in the segment construction environment is studied, and the correlation between the relative convergence displacement and the shield tunneling parameters is analyzed. Result & Conclusion The monitoring data indicates that the circumferential deformation mainly occurs within one week after the installation of the tunnel segments and within a 50 m range of the adjacent tunnel excavation. In condition of unfavorable stratum and small buried depth, the effect of the subsequent tunnel excavation on the convergence of the already constructed segments is about 50%. When the stratum is favorable and the buried depth is large, the effect of subsequent tunnel excavation on the above convergence is approximately 65% to 83%. The strain of the segments is affected significantly by the stratum and the adjacent tunnel construction under different buried depths. The segments in a shallow buried depth and poor soil stratum have large deformation, while those in the larger buried depth exhibit better constraint and unnoticeable deformation. There is a clear correlation between the relative convergence displacement and the shield tunneling parameters. The total thrust of the subsequent shield tunneling is negatively correlated with the relative convergence displacement of the previously constructed segments, while the excavation speed of the subsequent shield tunneling is positively correlated with the above relative convergence displacement. The real-time monitoring data obtained through FBG monitoring technology can serve as a basis for adjusting the shield tunneling parameters.

Keywords

• metro tunnel
• fiber bragg grating
• circumferential deformation
• construction period