Three-dimensional stability calculation method for high and large composite slopes formed by mining stope and inner dump in adjacent open pits

The 2D limit equilibrium method is widely used for slope stability analysis. However, with the advancement of dump engineering, composite slopes often exhibit significant 3D mechanical effects. Consequently, it is of significant importance to develop an effective 3D stability calculation method for composite slopes to enhance the design and stability control of open-pit slope engineering. Using the composite slope formed by the mining stope and inner dump in Baiyinhua No. 1 and No. 2 open-pit coal mine as a case study, this research investigates the failure mode of composite slopes and establishes spatial shape equations for the sliding mass. By integrating the shear resistance and sliding force of each row of microstrip columns onto the bottom surface of the strip corresponding to the main sliding surface, a novel 2D equivalent physical and mechanical parameters analysis method for the strips on the main sliding surface of 3D sliding masses is proposed. Subsequently, a comprehensive 3D stability calculation method for composite slopes is developed, and the quantitative relationship between the coordinated development distance and its 3D stability coefficients is examined. The analysis reveals that the failure mode of the composite slope is characterized by cutting-bedding sliding, with the arc serving as the side interface and the weak layer as the bottom interface, while the destabilization mechanism primarily involves shear failure. The spatial form equation of the sliding mass comprises an ellipsoid and weak plane equation. The analysis revealed that when the coordinated development distance is 1500 m, the error rate between the 3D stability calculation result and the 2D stability calculation result of the composite slope is less than 8%, thereby verifying the proposed analytical method of equivalent physical and mechanical parameters and the 3D stability calculation method for composite slopes. Furthermore, the 3D stability coefficient of the composite slope exhibits an exponential correlation with the coordinated development distance, with the coefficient gradually decreasing as the coordinated development distance increases. These findings provide a theoretical guideline for designing similar slope shape parameters and conducting stability analysis.