Monitoring and detection of internal erosion in unsaturated slopes

Abstract

Internal erosion is a major cause of failure in embankments and natural slopes, yet early-stage processes in unsaturated soils remain difficult to detect because subsurface flow paths develop below the ground surface and often produce no visible indicators. This research investigates concentrated leak erosion in unsaturated clayey sand and evaluates how hydraulic and mechanical sensing methods capture erosion-related responses during controlled large-scale experiments. Test slopes were constructed with full-pipe and partial-pipe defects and instrumented with volumetric water content (VWC) sensors, suction sensors, and a low-cost internal erosion (IE) sensor developed and calibrated as part of this study. VWC sensors recorded wetting-front movement, seepage migration, and the reactivation of preferential pathways, providing clear hydraulic precursors to erosion. Suction measurements did not contribute meaningful information due to loss of hydraulic continuity. The IE sensor detected localized deformations associated with pipe enlargement, collapse, and shallow sliding, capturing mechanical activity not reflected in moisture data. No single sensor type captured the full sequence of erosion processes, and the most complete interpretation emerged from combining distributed moisture sensing with deformation-sensitive instrumentation. These findings clarify how internal erosion progresses in unsaturated soils and provide a framework for integrating hydraulic and mechanical measurements into practical monitoring systems for early detection.