Seepage process understanding at long-existing landslide dams through numerical analysis and hydrological measurements

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Landslide dams consist of unconsolidated heterogeneous material and lack engineering measures to drain water and control pore water pressure. They may be porous and seepage through them could potentially lead to piping failure. In this research, the internal processes within a long-existing landslide dam are assessed under transient seepage force. The implemented approach includes a 3D finite element numerical simulation executing fully coupled flow-deformation and consolidation methods based on hydraulic data measurements and geotechnical laboratory tests. The nonlinear constitutive model ‘Hardening Soil’ is applied to accurately calculate the stress-induced pore water pressure, effective stress, deformation, and flow. Further, the possibility of slope failure due to seepage force is investigated through the strength reduction method. The results highlight the dependency of the seepage flow on the corresponding variation of the relative permeability and saturation in the soil mediums under different rates of seepage force. Small rates of seepage force, however, impose deformation at the dam's crown. High effective stress is obtained at negative small rates of seepage force where the long duration of fluctuation is modeled. In the drawdown simulation, there is a reverse relation between effective stress and the rate of the seepage force. Through the modeling process and based on the measured data, two seepage paths are detected within the landslide dam, while their activation depends on the lake level. The modeling approach and the required data analysis are suggested for utilization in further studies regarding the seepage process understanding at the long-existing landslide dams and their hazard assessments in addition to the common geomorphological approaches.