Research on the evolution and application of mining-induced fractures based on the optical frequency domain reflection technology

To investigate the evolution law of fractures in the overburden during pressure relief of fully mechanized mining faces in deep coal seams, similar simulation tests were conducted on the III 1022 fully mechanized mining face of Luling Coal Mine by adopting the optical frequency domain reflection (OFDR) technology. The resulting data allowed for analysis on the entire process of fracture evolution in the overburden. In this study, the temporal and spatial evolutions of fractures in the stope were explored on the basis of the on⁃site gas drainage data and the optical fiber monitoring results. The findings demonstrate that during the mining process of the working face, the tensile strain curve of optical fibers in the horizontal direction of the overburden in the goaf exhibits left and right peaks. The distance between two peaks represents the actual collapse width of the overburden, and the peak values of them correspond to the mining fracture lines on both sides of the working face. Meanwhile, the advanced abutment pressure exerts an influence in the vertical direction, leading to the concentration of compressive stress in front of the working face. The compressive strain curve of optical fibers tends to decline stepwise, with tensile strain peaks appearing in the roof and floor of the goaf. Furthermore, the evolution characteristics of mining-induced fractures in the working face were deduced in accordance with the gas concentration data at the upper corner of the working face, the pressure relief gas drainage data from the 1# interception borehole of the directional drilling field, and the pressure relief gas drainage data from the 5# surface well. Besides, according to on-site optical fiber monitoring results, the fracture zone in the stope has developed to a height of 77. 5 m, and the fracture layer of the overburden has reached the 8# and 9# coal seams. The research results are expected to provide a theoretical foundation for the design of mining technology in the working face, gas migration in adjacent layers, arrangement of drainage boreholes, and gas control, which is of great significance for promoting safe and efficient production in coal mines. © 2024 China University of Mining and Technology. All rights reserved.