A field study on distributed fiber optic deformation monitoring of overlying strata during coal mining

In this paper, the distributed optical fiber sensing technology based on Brillouin optical time-domain reflectometer (BOTDR) was employed to monitor and analyze the force and deformation of the overlying rock strata during the coal mining process in Huaibei, China. The selection and arrangement of the sensing cables were introduced, together with details on data collection and analysis. Four types of sensing cables were vertically installed into a borehole to monitor the strata deformation. The monitoring data were collected according to the mining schedule. The strain distributions and their variations with time were studied to reveal the deformation pattern of the overlying rock mass induced by coal mining. Results showed that during the mining process, there was a fracture surface at the bottom of the upper igneous rock layer. The separation phenomenon occurred along the fracture surface in the lower rock strata, which slipped obliquely to coalface. The rock beneath the bottom of the lower igneous rock layer was compressed due to periodic weighting of the overlying rock strata before the working face reached the monitoring borehole. The ground deformation gradually accumulated during the whole mining process. These results indicate that the BOTDR-based monitoring method is effective for capturing strata deformation induced by underground mining, and may open up new avenues for ensuring safe and efficient coal mining activities.