Study on the zoning deformation characteristics of coal pillars in a near-distance coal seam group based on distributed fiber optic sensing

Abstract

To investigate the impact of overlying remnant coal pillars on the underlying coal pillars under repeated mining conditions, within the context of near-distance coal seam group exploitation in a western mining district, this study was conducted in the 2⁻² coal seam at Daliuta Coal Mine, Huojitu Well. An armored optical fiber was embedded within the coal pillars, and based on Brillouin Optical Time-Domain Reflectometry (BOTDR) distributed fiber optic sensing (DFOS) technology, high-resolution, spatiotemporal dynamic decoupling and monitoring of the coal pillar strain field were achieved. It breaks through the limitation that traditional point sensors such as stress gauges and displacement meters cannot capture the spatiotemporal evolution of continuous deformation inside coal pillars, and overcomes the discrete measurement limitations of traditional methods. This facilitated revealing the evolving load-bearing structural patterns and mechanical response characteristics of two different segmental coal pillars under repeated mining cyclicity. Results indicate that, under repeated mining conditions, the fractured zone beneath the remnant coal pillar expanded by 84.42 %, with the load-bearing structure degrading into a “plastic zone-fracture zone” bimodal configuration, whereas the coal pillars beneath the goaf area maintained a three-zone structure comprising “elastic zone–plastic zone–fracture zone.” Numerical simulations demonstrate that the overlying remnant coal pillar creates high-stress anomaly zones, causing the underlying coal pillars to endure concentrated stresses significantly exceeding the distributed loads of the goaf, thus reconstructing the overburden-coal pillar mechanical system and increasing the likelihood of overall structural failure. This study quantitatively elucidates the differential degradation mechanisms of the two types of coal pillars. The application of armored fiber optic embedding combined with BOTDR-based distributed sensing provides a critical theoretical foundation and technical reference for the deployment of DFOS in deformation monitoring within geotechnical engineering in mining environments.