Stress Monitoring for Anchor Rods System in Subway Tunnel Using FBG Technology

Abstract

This paper presents a model test, used on the tunnels on Xi’an Metro Line 2, as the prototype for evaluating the reinforcing effect of the anchor rod in tunnel construction in loess areas. An independently designed fiber Bragg grating (FBG) sensor was used to monitor the seven strain conditions of the rock bolts during the construction. The result shows that the axial stress of the rock bolt changes after the excavation and increases steadily with the growing pressure in the wall rock. Results additionally show that the anchor rods at the tunnel vault are subjected to a compressive stress that remains relatively constant after the primary and the secondary lining, while those at the spandrel and the corner of the tunnel are subjected to increased tensile stress. This paper demonstrates the feasibility and the superiority of FBG technology for tunnel model tests.

Fiber Bragg Grating Sensors-Based In Situ Monitoring and Safety Assessment of Loess Tunnel

“…Roveri et al [28] presented the results of a field trial with a FBG sensor array system for the realtime monitoring of railway traffic and for the SHM of both the railway track and train wheels. Weng et al [29][30][31] developed a FBG-based sensor network to monitor the strain distributions in the pavement structure, axial stress of tunnel anchor, and foundation settlement; moreover, the centrifugal model test was performed with an improved packaging and installation method for the quasi-distributed sensor system. In view of the aforementioned studies, in situ monitoring through installation of sensors is a widely used method for the investigation into the mechanical properties and strain changes of tunnel liner with better accuracy and reliability [32].…”

Construction Technique of Long-Span Shallow-Buried Tunnel Considering the Optimal Sequence of Pilot-Tunnel Excavation

“…Although the tunnel deformation and settlements could be well controlled by successive excavation, the problems like long construction period and low economic benefits would appear. Thus, in the interest of improving the excavation speed, the following three simultaneous multi-pilot-tunnel excavation methods were analyzed and compared for the optimal one [17,18]. in Figure 4, and the arch apex displacement curves are shown in Figure 5.…”

Analysis of the highway tunnels monitoring using an optical fiber implemented into primary lining

“…Fibre Bragg gratings are implemented together with anchoring bars that serve for the reinforcement of rock bodies. This approach is used to monitor the stress and deformation levels in the anchors, and it enables warning of rock mass movement and its failures [19][20][21][22][23]. FBG are also used for the measurement of deformation in the secondary lining of tunnels [24][25][26][27] where quasi-distributed measurement with the help of multiplex techniques can be used [28,29].…”