Research on the overburden deformation and migration law in deep and extra-thick coal seam mining

To understand the problem of water damage to the roof caused by instability and deformation of overburden deep coal seams in the Ordos mining area, the rock stratum migration mechanism was analyzed according to the geological conditions of the Tangjiahui coal mine, and a vertical borehole observation system was established based on the stress characteristics and the migration model of the rock beam. The comprehensive monitoring methods of Brillouin optical time-domain reflectometer (BOTDR) and borehole resistivity were used to analyze the "optic-electric" evolution law of overburden during mining, and together with the calculation of the empirical formula, the spatiotemporal information of overburden migration was determined to guide the work in preventing water damage to the roof. According to the results, the roof lithology and stratum structure have a significant effect on the overburden failure law; deformation failure occurs first in strata that are soft or contain many fissures; the stratum collapse and stress state develop in the shape of "steps" from bottom to top and the horizontal and vertical stresses have zoning and time-sequence characteristics; the development heights of the caving zone and fractured zone are approximately 75 m and 205 m, respectively; and the influence distance of the shear stress of early mining is approximately 92.7 m. The method of monitoring overburden deformation and failure based on distributed optical fiber sensing provides a new test method for the prevention and control of water damage in mines with similar geological conditions. (C) 2021 Elsevier B.V. All rights reserved.