Abstract
Rock bolts have been widely applied with roadway excavation in underground coal mines to prevent roadway collapse and improve the stability of roadway surrounding rocks. Overloading and failures of rock bolts could result in accidents or casualties in coal mine roadways. Consequently, monitoring axial forces and work conditions of rock bolts plays an increasingly important role in ensuring safe operations of underground coal mines. Conventional mechanical or electronic rock bolt monitoring systems are typically affected by electromagnetic interference, corrosive groundwater, and dusty circumstance in underground working sites. This work proposed a FBG-based instrumented rock bolt. Quasi-distributed FBG sensors were installed on a slotted rock bolt and encapsulated by epoxy resin that was used to fix FBG sensors on the rock bolt and protect FBG sensors from damage. The FBG sensors were calibrated before the in situ application. Monitoring results indicated that the axial forces of rock bolts installed on the roof of the roadway were higher than that of others, and the maximum axial forces of each rock bolt were typically detected near the middle portion of rock bolts. A real-time and accurate rock bolt monitoring system was established by integrating instrumented rock bolts to the existing monitoring system of the coal mine.
Highlights
As the coal resources within shallow grounds are depleting and coal mining operations are moving to deeper grounds, approximately 60% of the coal mining works are currently conducted with a mining depth of over 800 m in China [1]
This paper proposed a steel fiber Bragg grating (FBG)-based instrumented rock bolt for monitoring of axial force of rock bolts
The instrumented rock bolts were used to measure axial forces of rock bolts, and the FBG temperature sensors were implemented to correct the error of measuring data which was caused by temperature variations
Summary
As the coal resources within shallow grounds are depleting and coal mining operations are moving to deeper grounds, approximately 60% of the coal mining works are currently conducted with a mining depth of over 800 m in China [1]. Zhao et al [14] developed a monitoring cylinder fitted with FBG sensors for measuring axial force of rock bolts. These devices increased monitoring accuracy of rock bolt load monitoring. Current instrumented rock bolts are made up of plastic or polymer materials, and the optical fiber sensors are capable of being embedded within the FRP rock bolts during the manufacture stage [17, 18]. This paper proposed a steel FBG-based instrumented rock bolt for monitoring of axial force of rock bolts. An early warning can be obtained before rock bolt failure by integrating the instrumented rock bolt into a monitoring network of the coal mine
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