An Investigation of a Floor Treatment Plan for In-Pit Dumps with an Underlying Weak Layer

To effectively manage the stability of in-pit dumps with an underlying weak layer, a new plan for the treatment of a staged floor during the life of a mine was proposed in this study. Based on direct shear test results, the shear properties of contact surfaces between the weak layer, dumped spoil, and mudstone were determined. Taking the Baiyinhua No.1 Open-pit Mine as an example, a direct shear test of the contact surface between the spoil and the mudstone determined its cohesion to be 25.78 kPa, and the internal friction angle was 17.58°. The cohesion of the contact surface between the spoil and the weak layer was 7.50 kPa, and the internal friction angle was 9.72°. Different floor treatment rates were subsequently determined based on discontinuous structural surface and limit equilibrium theories. The in-pit dump plan was divided into stages based on a 10-year mine plan; a “safety reserve coefficient” was used as the conditional factor to calculate the minimum floor treatment rate. The results of a numerical simulation analysis of the slope stability of the untreated and treated inner dumps showed good agreement with results obtained by the limit equilibrium method. The position and shape of the sliding surface were also found to be similar, indicating the validity of the established numerical simulation model and the reliability of the calculated results. Based on field application and economic effect analysis, it was found that this proposed method can minimize the floor treatment rate effectively while maintaining a sufficient factor of safety. The direct economic benefit of this method was approximately 1,694,259 dollars at the Baiyinhua No.1 Coal Mine. This method is of great significance to safe and efficient production, and can be widely applied.