Evaluation of viscosity adjustment effects on the mechanical properties of grouting used in high-bench slopes

In this work, polyurethane grouting materials were applied for the first time to reinforce high bench slopes in open-pit coal mines. To address the issue of high viscosity, the effect of viscosity modifiers on the structure and mechanical properties of two-component polyurethane grouting materials was investigated. By adjusting the concentration of the viscosity modifier, it was found that increasing in modifier content led to a decrease in the tensile, shear, compressive and bond strength of the specimens. This trend was attributed to the reduction in carbamate content caused by the decrease in reactants. In the field reinforcement experiment, the polyurethane grouting material with 12.5% viscosity modifier exhibited a bond strength of 5.2 MPa, compressive strength of 30.1 MPa, shear strength of 5.5 MPa and tensile strength of 9.5 MPa. A grouting scheme was designed and implemented for a 6 m-long crack, with a total grouting amount of 940 kg, effectively sealing the top of the crack and preventing water infiltration. Monitoring results over a total of 135 days, including 45 days before grouting and 90 days after grouting, revealed that the crack dimensions did not increase, instead, its dimensions decreased. Furthermore, the crack rate of change transitioned from fluctuating to stable.