Experimental Study on Load-Transfer Mechanism of Rockbolts Using Fiber Optic and Strain Gauge Monitoring

Abstract

As a cost-effective rock-supporting method, rockbolts have been widely used in geotechnical and mining engineering. Better understanding the load-transfer mechanism of rockbolts is of great importance for improving the accurate simulation of rockbolts applied in practical engineering. Numerous experimental studies on rockbolts have been conducted, and conventional instruments, such as strain gauges, have been used to monitor the deformation of rockbolts. Although researchers have reported on fiber optic-based monitoring, these data have not been verified by accurate strain gauges. In addition, there has been limited study on utilizing the fiber optic method to monitor the full range strain variation of rockbolts across varying rock strengths. In this study, distributed fiber optic sensing (DFOS), with an ultrahigh spatial resolution (0.01 mm), and strain gauges (SGs) were used to monitor the strain variation in rockbolts under pull-out tests, with the aim of comparing the performances of the DFOS and discrete strain gauges and determining the reliability and advantages of DFOS. It was found that: (1) the fiber optic data were able to perfectly reflect the complete decoupling mechanism of the bolt, which could not be observed in the strain gauge data; (2) the ultrahigh spatial resolution of the fiber optic method enabled it to accurately and fully exhibit the distribution of shear stress along the bolt; and (3) high rock strength can enhance the bonding performance of bolts and result in uneven stress distribution.