The Application of Distributed Fiber-Optic Sensing Technology in Monitoring the Loose Zone in the Floor of Stoping Roadway

The bulking and extrusion of loose rocks within the floor's loose zone in stoping roadways are the primary causes of significant floor expansion and deformation. A force and deformation model for the optical fiber sensing within the loose zone of the floor has been developed to apply distributed optical fiber sensing technology for monitoring the floor's loose zone. This paper presents the characterization and calculation method of the distributed optical fiber strain curve for determining the development range, expansion displacement, and expansion stress of the roadway floor's loose zone. The extrusion coefficient (xi) quantifies the extrusion characteristics of loose rocks within the floor's loose zone. Borehole-implanted sensing optical fibers were employed to monitor the depth, expansion displacement, and expansion stress of the roadway floor's loose zone during mining operations at the 21,104 working face in Hulusu Coal Mine. The maximum development depth of the loose zone in the roadway floor of Hulusu Coal Mine is 4.23 m, with a maximum expansion displacement of 0.446 m. The expansion displacement generated by the loose zone exhibits a quadratic function relationship with its development depth. The maximum expansion stress sensed by the optical fiber is 2.4 MPa, with the expansion stress generated by the loose zone exhibiting a linear relationship with its development depth. The extrusion coefficient (xi) for the sandy mudstone floor of the 21,104 working face at Hulusu Coal Mine ranges approximately from 1.04 to 1.13. The measured values obtained from the optical fibers show good consistency with the numerical simulation results in both trends and numerical values. Distributed optical fiber-sensing technology can effectively monitor the loose zone, expansion displacement, and expansion stress of the mining roadway floor during mining operations, enabling extensive, long-distance, all-weather, and real-time monitoring of roadway surrounding rock. A model for the force and deformation of the optical cable within the loose zone of the floor has been developed.A method for characterizing and calculating the distributed optical fiber strain curve is provided for the development range, expansion displacement, and expansion stress within the loose zone of the roadway floor.An extrusion coefficient (xi) has been defined to quantitatively characterize the extrusion behavior of loose rock in the loose zone.