Estimation and application of local replacement rate for soft foundation in inner dump based on strength parameters: A case study of Baiyinhua No. 1 open-pit mine in Inner Mongolia

In order to effectively enhance the stability of the slope within the soft base of the inner dump, this study focuses on the Baiyinhua No. 1 open-pit mine as the engineering background. Through direct shear tests, the shear mechanical characteristics of the waste-weak layer interface and the waste-sandstone interface were determined. A methodology is proposed to determine the equivalent shear mechanical parameters of the waste-base interface under localized replacement conditions. In this study, the limit equilibrium theory of rigid body is applied to calculate the slope stability coefficients under different replacement ratios. Additionally, an estimation method for the local replacement ratio of the soft base in the waste dump, based on strength parameters and subject to a safety reserve coefficient constraint, was put forward and verified using numerical simulations. The results indicate that the cohesive force and internal friction angle at the waste-sandstone interface in the Baiyinhua No.1 open-pit mine were determined to be 25.78 kPa and 17.58°, respectively. These two parameters at the waste-weak layer interface were found to be 7.50 kPa and 9.72°, respectively. A positive linear relationship was observed between the stability coefficient of the inner dump slope in the soft base under localized replacement conditions and the replacement ratio. The calculated results reveal that a replacement ratio of 20% for a certain stage of the dump's base satisfies the safety reserve coefficient requirement. After local replacement treatment, the landslide mode of the dump slope in the soft foundation remains characterized by combined sliding, with the arc acting as the lateral boundary and the weak base layer serving as the bottom interface.