Key technologies and engineering applications of intelligent optical fiber monitoring for section coal pillars

The deformation zoning of section coal pillars under mining-induced stress is the prerequisite for guiding the design of support parameters and the control of surrounding rock stability. Exploring the evolution of deformation zoning and precursors to instability is crucial for revealing the mechanisms of coal pillar instability leading to disasters and preventing related disasters. This paper, based on the research background of close coal seams in Huojitu Well of Daluta Coal Mine, adopts theoretical analysis and on-site monitoring with optical fiber sensors to conduct optical fiber monitoring of section coal pillars during working face mining. A technical scheme and system for optical fiber monitoring have been established, systematically studying the theory of internal deformation zoning and characterization of coal pillars under mining-induced stress using optical fiber monitoring. The results show that the maximum horizontal strain of the coal pillar during the first mining-induced stress was 1252.06με, with the minimum value at 47.93με; the strain on the mining side was about 26 times greater than that on the non-mining side, and the strain curve generally exhibited a unimodal distribution with an approximate linear growth trend. During the second mining-induced stress, the maximum strain value was 1100.94με, with the minimum value at -164.26με, and the strain curve generally showed a U-shaped distribution with an approximate linear growth trend, with the strain of the coal pillar under the second mining-induced stress being approximately 3.46 times that of the first. Under the superposition of the first and second mining-induced stresses, the horizontal strain of the coal pillar showed a bimodal trend, with more significant changes closer to the side of the first mining-induced stress. The ranges of the elastic, plastic, and fractured zones of the coal pillar under mining-induced stress were determined: during the first mining-induced stress, the width direction 0~10.1m was the elastic zone, 10.1~12.8m the plastic zone, and 12.8~15m the fractured zone. After the second mining-induced stress, the width direction 0~1.1m and 2.8~7.3m became the elastic zones, 1.1~2.8m and 7.3~9.1m the plastic zones, and 9.1~15m the fractured zone. Field measurements verified that the horizontal strain of the coal pillar under the second mining-induced stress mostly showed a bimodal distribution, confirming the general rule that the strain on the coal pillar side of the first mining is greater than that on the side of the second mining.