“Four Zones” control model and application for surface subsidence of bed separation grouting mining

The grouting technology of bed separations has been proved to be a new method which can meet the requirements of non-destructive mining and solid waste reduction. To effectively control the subsidence of ground structures caused by mining, the whole process of bed separation grouting mining is analyzed in a steady state based on the key stratum theory. For the first time, a “four zones” control model for surface subsidence under grouting bed separation was proposed, which includes natural zone, transition zone, warning zone, and protection zone, and the calculation formula for the "four zones" range was derived. Based on the engineering back-ground of controlling the subsidence of the ground coking plant at the 3501 panel, the proposed “four zones” model was validated by combining physical model-ling and field measurement of subsidence. The results show that the surface subsidence curve of bed separation grouting in physical model-ling shows an irregular “V” shape, and the surface subsidence of the panel first increases rapidly. After reaching the maximum subsidence, the surface subsidence first decreases rapidly, and then the reduction rate gradually slows down. The subsidence curve shows a clear “four zones” distribution, with a maximum subsidence of 1 589 mm, appearing at the contact boundary between the natural zone and the transition zone. The subsidence of the contact boundary between the transition zone and the warning zone is 497.94 mm, and there is basically no subsidence within the protection zone. The predicted surface subsidence, horizontal deformation, slope, and curvature caused by mining under grouting conditions based on probability integral method are consistent with the field measured results, but significantly smaller than the predicted values under non-grouting conditions. It is determined that the surface deformation under grouting conditions meets the requirements of Grade I damage level for structures. Based on the practical engineering geology and observed data of the mine, the natural area is 261.19 m, the transition area is 246.09 m, the warning area is 655.25 m, and the protection area is 199.53 m. The proposed “four zones” control model provides a fundamental theoretical basis for studying the subsidence of bed separation grouting mining. © 2023 China Coal Society. All Rights Reserved.