Research on Mechanical Behavior and Energy Evolution of Coal and Rocks with Different Thin Spray-On Liners Thickness under Uniaxial Compressive Loading

Compared with the traditional supporting materials such as the bolts, mesh, and concrete, thin spray-on liners (TSLs) have the advantages of improving impact energy bearing and absorption capacity of rocks. In this study, the uniaxial compressive mechanical response feature of white sandstone, yellow sandstone, and coal with different coating thickness of TSLs were investigated through laboratory tests and theoretical analysis. The hard segments and soft segments of TSLs induced microphase separation, and formed the physical cross-linking. The hard segment evenly dispersed in the soft segment, which improved the mechanical strength of the TSLs. The confining pressure was affected by the TSL-coated coal and rocks, which improved the mechanical strength of the rocks and coal under UCS loading. It was discovered that the uniaxial compressive strength (UCS) increases with an increase in the TSL coating thickness, and UCS increments of the coated white sandstone, yellow sandstone and coal were 4.6%, 25.51%, and 43.75%, respectively. The energy absorption capacities of the coated coal, and yellow and white sandstones gradually decreased with an increase in their TSLs coating thickness. Meanwhile, the energy-absorbing capacity of a coated rock reduced gradually as rock coating decreases. Furthermore, the energy-absorbing capacity of coal is greater than that of yellow sandstone or white sandstone. By increasing the coating thickness, the total and dissipative energies in the yellow sandstone, white sandstone, and coal specimens were gradually increased, and energy increment was significantly more in coal (2–3 times), while the elastic energy remained nearly unchanged.