Experimental study on surface protection support that uses polymer thin spray-on layer

The thin spray-on liner (TSL) is widely used in the seal engineering of mines. TSL with high bearing capability is a new method that can be used to replace metal mesh in the roadway support of underground coal mines. This method exhibits the advantages of fast development, automation, and applicability of geo-conditions. The support theories of TSL are analyzed based on the deformational process of TSL in soft rock roadways. The analysis shows that TSL coheres and repairs the surrounding rock surface to form a bonding layer, exerting a confinement effect on the deformation of deep rock masses. Under a large deformation of the surrounding rock, TSL forms a thin shell structure, which produces a supporting effect. Experiments were conducted to compare the supporting effects of different surface protection methods by using large-scale briquette coal pillar samples and a newly developed polymer TSL material. Results show that the confining effect of TSL is greater than that of the metal mesh, and the bearing capacity of the sample is increased by 28.3%. The residual strength of the TSL specimen is also higher, and the energy dissipation of the system increases by 44.1%. The supporting effect of the TSL thin shell structure was experimentally studied for the first time on different rock masses. The results showed that the TSL shell structure reduced surface rock deformation by bearing compressive stress, and the bearing capacity of lignite and sandstone samples increased by 44.6% and 20.4%, respectively, while energy dissipation increased by about two times. A numerical method was used to analyze the stress distribution of TSL and the mechanism of the surrounding rock deformation in the experiments. The results were compared with the experimental observations. This study provides a theoretical basis for the practice of TSL support engineering and an experimental research method for predicting the effect of TSL support in underground coal mine roadways.