Monitoring the safety status of service bolts in mining roadways.

To monitor the safety status of the bolts in coal mining roadways in real time, the safety and stability of the bolt support structure were evaluated. Based on the conventional support bolts used in the field, a fiber Bragg grating (FBG) sensor and medium materials were selected. Through theoretical analysis, the bolt tension, and FBG temperature tests, the strain transmission mechanism of the FBG bolt was analyzed, and it was ensured that the developed FBG bolt could accurately measure the strain of the bolt. In the field test, FBG bolts were arranged on the positive and negative sides of the mining roadway to accurately monitor the safety status of the bolts in service in real time, and the force characteristics of the bolts monitored by the FBG sensor were analyzed to obtain the maximum axial force of the positive and negative bolts. Thereafter, the safety status of the roadway bolt was evaluated. The results show that the positive side bolts axial force change is significantly greater than that of the negative side bolt; with the working face advancing to a distance of 60 m from the bolt as the dividing line, the positive side bolts axial force grows slowly before this, after which the axial force increases rapidly. The locations of the roadway where the positive and negative bolts are most affected by mining are determined, and roadway support and prevention measures for this location should be conducted in time. The safety status of the bolts is evaluated and monitored as follows: the positive side No. 2, No. 3, No. 5, and No. 6 bolts have reached the failure state, the positive side No. 4 bolt is in a dangerous state, the positive side No. 1, negative side No. 8 and No. 9 are in an abnormal state, and the negative side No. 7, No. 10, No. 11, and No. 12 are in a normal condition. This research has laid a technical foundation for the real-time monitoring of the bolt support of the mining roadway and the assessment of the safety status of bolts.