Multiscale Physical Model on Internal Erosion in Unsaturated Slope

Abstract

Soil piping is the gradual and progressive erosion of soil grains, causing a void (open pipe) to form as water flows through the soil. In dam engineering, this type of internal erosion is often referred to as concentrated leak erosion and has been a cause of failure at multiple dams. Soil piping has also been observed in many landslides and contributes significantly to soil degradation in hillslopes and agricultural areas. Eroded pipes may act as a natural drain and increase stability if they remain open, but they may decrease stability if pipes collapse or become blocked and increase pore pressures in the slope. Despite these many important impacts, there is still a limited understanding of how soil pipes develop and progress, and what factors control pipe and slope stability. One of the significant challenges with analyzing soil piping, or concentrated leak erosion, is that it typically occurs in the vadose zone, where unsaturated conditions are present. Previous studies have investigated the effects of various parameters on the piping process. However, few have examined how the hydromechanical response of the slope is affected by pipe erosion or collapse. Consequently, this study used physical models of unsaturated slopes to examine how soil properties, pipe characteristics, and hydraulic conditions affect the progression of internal erosion and initiation of shallow landslides. Sensors and cameras were used to monitor the slope response to subsurface flow, and post-test pipe measurement was conducted. Multiscale experiments were performed to explore the effects of pipe condition (no pipe, partial or closed pipe, and full or open pipe), bed slope angle, pipe configurations, and compaction properties on the hydromechanical response of an unsaturated slope. These experimental results demonstrate that unsaturated soil properties (dry density and initial moisture content), pipe conditions, slope angle, and soil type control the hydromechanical response of the slope. Numerical simulations of stability and erosion exhibited consistency with the experimental results. The study identified key limitations and outlined promising directions for future research.