Physical modeling of the controlled shaft deformation law during the solid backfill mining of ultra-close coal seams

Solid backfill mining has gradually become the key technology to control shaft deformation during industrial square coal pillar recovery. The industrial square area of the Nantun coal mine was studied in this paper. Based on similarity criteria of the physical modeling, an experimental model was designed to study the shaft deformation law under caving mining and backfill mining. A non-contact full-field strain measurement system and a resistance strain gauge were adopted to monitor the model. The mining-induced deformations, failures and stress distributions of shaft-surrounding rock masses during the recovery of industrial square coal pillars by caving mining and backfill mining were explicitly compared and analyzed. The results showed that the deformation and failure of shafts was caused by strata movements during the mining of the coal seams. Different lithology, stiffnesses, and thicknesses of adjacent rock strata result in asynchronous stratum movements, which thus cause shaft failure. The key to controlling mining-induced deformation of shafts during solid backfill mining is to control strata movement as follows: solid backfilling → control of the strata movement → control of the shaft deformation → decrease of the tension and shear force experienced by the shaft → decrease of shaft damage. Finally, the design method of the backfill body’s compression ratio based on shaft deformation control during the solid backfill mining process is proposed, thus laying the foundation for the safe recovery of an unexploited coal industrial square in resource-exhausted coal mines.