Strain-Sensing Mechanism and Axial Stress Response Characterization of Bolt Based on Fiber Bragg Grating Sensing

The anchoring quality of bolts is related to roadway safety and the surrounding rock stability. Due to the limitations of conventional monitoring methods in capturing strain, there still exists a gap in the real-time perception of the mechanical properties of bolts at the micro-scale. This paper proposes a new approach to detecting bolts’ anchoring qualities based on the fiber Bragg grating sensing principle. Moreover, it studies the strain transmission mechanism between the surface-bonded fiber Bragg grating and the bolt. A fiber-optic monitoring test platform of anchor bolt anchoring quality is built. The full-length anchor bolt’s strain evolution law and axial force distribution characteristics are studied during the pull-out test. The study results have shown that the theoretical value of the fiber strain transfer coefficient can be used to calculate the strain of the bolt. The bolt pull-out test verified the accuracy of using the fiber Bragg grating bolt axial force characterization equation to estimate the bolt stress. On the other hand, the correlation between the bolt axial force and the fiber Bragg grating monitoring value follows an exponential pattern. This study provides an important basis for improving the understanding of a bolt anchoring mechanism and the stability control of a roadway’s surrounding rock.