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Expansive soils are widespread in the world and coincide with areas of high human activity. The main cause of deep instability of expansive soil slopes is due to their softening caused by excavation and seepage. By developing a comprehensive numerical model based on the theory of unsaturated soil, this study examines the characteristics of stress and displacement distribution of expansive soil slopes through hydraulic‐mechanical coupled numerical simulation. This study analyzes the evolution patterns of slopes with excavation unloading and seepage of water storage to reveal the mechanisms of deep‐seated instability of expansive soil slopes. The findings demonstrate that: The instability of expansive soil slopes begins at the foot of the slope and propagates along the interlayer, affecting the entire slope. Excavation leads to the softening of the expansive soil interlayer and the transfer of shear stress. During water storage, the weakening of the soil strength results in slope instability along the weak interlayer slip. Softening of the expansive soil interlayer facilitates the redistribution of shear forces in the slope and alters the distribution law of the plastic zone in the deep layer. Overly slowing down the slope leads to significant excavation unloading, which is detrimental to the slope's stability. [ABSTRACT FROM AUTHOR]

The management and knowledge of landfills are generally inadequate and could lead to significant catastrophes. This is particularly concerning for solid waste landfills due to their large size and potential to threaten nearby structures and residents in the event of landslides. In this paper, we investigated a backfill landslide induced by road construction in a coal mine slag landfill. Our analysis of satellite images and field surveys revealed that the alteration of the mounding morphology at the slope's crest by construction triggered the landslide. We established an engineering geological model of the main sliding plane and utilized the discrete-element program MatDEM to reproduce the landslide's development and predict its final accumulation pattern and impact range. Our study highlights the potential dangers of engineering construction carried out on relatively stable solid landfills. The combined in situ and numerical analysis research methods employed in this study can provide important references for risk assessment and treatment measures. [ABSTRACT FROM AUTHOR]