Effects of density and slope angle on internal erosion in an unsaturated clayey sand slope

Soil piping is a major contributor to soil erosion in many parts of the world, and collapse of eroded voids (pipes) can result in the formation of gullies and sinkholes or trigger slope instability. In dams and levees, soil piping is referred to as concentrated leak erosion and is one of the most dangerous forms of internal erosion. Despite these significant impacts, there is little understanding of factors controlling pipe collapse, and how water within the pipe influences moisture levels within a slope. In this study, physical models were used examine the development, enlargement, and possible collapse of eroded pipes in unsaturated slopes. The objective of these studies was to investigate how soil properties, pipe characteristics, and hydraulic conditions govern internal erosion processes and the connection between internal erosion and slope stability. Experiments used small initial defects to establish preferential flow paths, while systematically varying parameters including initial compaction moisture content and density, pipe condition (absent, closed, or open), slope angle, and model dimensions. Volumetric water content sensors monitored moisture evolution, while cameras captured slope responses to subsurface flow. Pipeflow rates, sediment concentrations, changes in pipe geometry, and post-test pipe features were analyzed to assess internal erosion dynamics.