Dynamic detection and analysis of overburden deformation and failure in a mining face using distributed optical fiber sensing

Abstract

The deformation and failure of overburden has been a major and challenging issue in the prevention of geological disasters in mines. In this study, Brillouin optical time-domain reflectometry is introduced to detect overburden deformation and failure. To use this technique, several boreholes are drilled in the top of a coal seam in a laneway, and optical cables are arranged in the boreholes to form a two-dimensional measurement cross section. During different periods throughout the mining process, the strain characteristics of the optical cables in the boreholes can be collected and dynamically analyzed to study the mining-induced changes in the strain in the overburden. This analysis can provide effective technical parameters for safe production in mines. A distributed optical fiber sensing (DOFS) test was conducted in the working face of a coal mine in Inner Mongolia, and a total of 25 sets of effective test data were obtained. The dynamic development characteristics of the overburden stress, deformation, and failure due to mining are analyzed. The characteristics of the strain distribution in the borehole are closely related to the orientation of the boreholes. Based on the strain distribution characteristics along the optical cable, the locations of the breakpoints, and the geological data of the 3-1 coal seam (where '3-1' is the indication code of the coal seam), the caved zone and the fractured zone extend 17 m and 48 m above the coal seam, respectively. These results are basically consistent with those from borehole resistivity computed tomography analyses. The results indicate that DOFS technology provides high-resolution results and is a good monitoring approach. Additionally, this technique can accurately determine the characteristics of overburden damage and has favorable application prospects.