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

Xiaolin Weng,Haohao Ma,Jun Wang

doi:10.1155/2015/480184

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.

Highlights

Assessing the condition and monitoring the health of structures make up an integral part of civil engineering, where there is an ongoing need to estimate the response of structures under particular loading and environmental conditions [1, 2]
The stress of anchor rods can be obtained through the calculation with the following equation: σ = Eε, (4)
Where E is the modulus of anchor rods

Summary

Introduction

Assessing the condition and monitoring the health of structures make up an integral part of civil engineering, where there is an ongoing need to estimate the response of structures under particular loading and environmental conditions [1, 2]. Despite being adequate and reliable, these conventional techniques are not suitable for real-time, in situ assessment of structures. These limitations can be overcome by using electrical-resistance strain gauges [2, 8], acoustic emission [9, 10], or optical fiber sensors [11,12,13]. In 1978, Hill et al first discovered the photosensitivity of the optical fiber, a discovery that eventually led to the occurrence of the fiber grating [15] The application of this device as a sensor was first reported by Morey late in 1989. The FBG-based model test—applied to the subway tunnel in a loess area—presented in this paper validates the reinforcing effect of the anchor rods

Working Principle of Fiber Grating

Tunnel Model and Test

Test Results Analysis

Numerical Analysis of Anchor Rods

Conclusions