Numerical investigation of deformation mechanism and treatment measures of landslide deposit: a case from Lancang river

This study focuses on the Zhenggang (ZG) landslide deposit along the Lancang River, aiming to clarify its deformation mechanism and propose targeted mitigation measures. Field surveys and monitoring data indicate that rainfall and groundwater are key factors affecting slope stability. Using saturated–unsaturated seepage theory, numerical simulations were performed to analyze perched water distribution under heavy and prolonged rainfall. Results show that perched water tends to accumulate in gentler sections of the sliding zone, with a maximum thickness of 8.29 m observed 3 days after rainfall. To address this, drainage tunnel schemes were proposed. Simulations of three-layer and five-layer tunnel configurations demonstrated significant reductions in perched water, particularly in the middle and rear sections. The five-layer scheme achieved over 40% reduction in maximum perched water thickness. Post-rainfall water remained mainly near the third sliding zone and X2 profile. Stability calculations revealed substantial increases in the point safety factor after drainage implementation. The proposed measures have been adopted in the ongoing ZG landslide management project, with the first tunnel layer under construction. This study provides practical strategies and simulation-based insights for managing perched water-induced landslides in similar geological settings.