Influence of thin spray-on layer (TSL) wrapping support on the spalling failure characteristics of sandstone

The safety and stability of underground structures can be enhanced by using a novel support material known as the thin spray-on liner (TSL). This material forms a continuous and robust protective layer on rock surfaces leveraging its superior bonding properties and tensile strength. However, the performance of TSL under the dynamic loading conditions caused by mining disturbances requires further investigation. To address this, the Split Hopkinson Pressure Bar (SHPB) spalling tests were conducted on TSL and mortar coating specimens with varying coating length and thicknesses. High-speed photography was employed to capture the spalling failure process of specimens in detail. The experimental results revealed that the bonding force between the TSL and rock decreased as the TSL's coating thickness increased. Compared to the uncoated sandstone specimens, the spalling strength of TSL-coated specimens was lower. Nevertheless, the spalling strength increased with greater TSL thickness and length. Initial cracking was observed at the interface between the coating and the rock. Similar patterns were noted for the mortar-coated specimens, although they exhibited different supporting mechanisms and higher layer cracking strengths. Additionally, FLAC3D-PFC3D coupled modeling was utilized to validate the experimental findings. The numerical simulation results aligned closely with the experimental data under identical impact loading. But when the impact load increases, the spalling strength of the TSL-coated specimen decreased with greater TSL coating thickness and length. The research results can aid in optimizing the design of support structures for underground roadways and serve as a reference for evaluating their stability.