Three-Dimensional Physical Similarity Simulation Experiments for a Transparent Shaft Coal Pocket Wall in Coal Mines

To explore the variations of the loading, deformation, and loss and to determine the mechanical state, loss characteristics, and stability for the shaft coal pocket wall in coal mines under a dynamic-static load, this paper innovatively attempts to conduct a three-dimensional physical similarity test of a transparent material shaft coal pocket, as well as the experiments of loading and unloading coal in the shaft coal pocket using different bulk storage materials 80 times. Then, the deformation, pressure, the surrounding rock, and the flow pattern of the silo wall were discussed considering the existence of the warehouse wall support. The characteristics of shaft wall deformation and surrounding rock stress cracks during the unloading were analyzed with the help from multiple integrated test systems such as strain gauges, pressure sensors, borehole peeps, and other comprehensive test systems. The results indicated that different dispersion particles have a significant impact on the strain of the shaft wall. When using the coal particles as storage materials, the overpressure coefficient of the shaft wall is up to 1.95 times higher than using dry sand particles. The particle size and internal friction angle of the bulk particles impact significantly on the deformation of the wall, where the cohesive force among the dispersed particles produced by the compaction effect has a certain influence on the side pressure of the silo wall. During the unloading process, coal particles were easier to obtain an arching phenomenon than dry sand particles. In addition, the number of bulk arching could be significantly reduced under the conditions of the warehouse wall support. The "weak rock stratum" in the surrounding rock plays a major role in controlling the deformation and failure development of the shaft wall. The three-dimensional physical simulation experiment of the transparent shaft wall truly reproduces the field engineering practice, and the physical simulation results are verified by numerical simulation analysis.