Waste Dump Slope Stability and Toe Berm Stabilization Under Moisture-Induced Strength Degradation of a Thick Soft Loess Foundation

A waste dump at a copper–molybdenum mine in Chifeng, Inner Mongolia, China, was investigated. Direct shear tests, three-dimensional finite element analysis, and field monitoring were used to investigate the effects of moisture-induced strength degradation of the loess foundation on slope stability and the effectiveness of toe berms. As water content increased from 10% to 18%, the cohesion and internal friction angle of the loess decreased by 74.1% and 15.0%, respectively. As the shear strength of the foundation decreased, deformation became increasingly concentrated near the slope toe. A continuous shear strain band developed from the toe into the loess foundation, while the factor of safety (FoS) decreased from 1.93 to 1.08. Field monitoring showed that cumulative horizontal displacement increased from the crest toward the toe, a spatial pattern qualitatively consistent with the numerical results. With the 20 and 40 m toe berms, FoS increased to 1.25 and 1.35, respectively. With the 40 m berm, the maximum absolute vertical displacement in the model and maximum shear strain decreased by 81.0% and 74.1%, respectively, compared with the case without a berm. These results help characterize the stability of waste dumps with similar thick soft loess foundations and the effects of toe berms.