Assessing levee stability: an investigation into early indicators of internal erosion from culvert defects

Levee stability can be compromised by internal erosion associated with culvert defects, yet early-stage erosion may not produce visible surface deformation. This study investigates the hydro-mechanical response of levees subjected to defect-driven internal erosion using four 20g centrifuge experiments. Instrumentation included pore pressure transducers, depth-sensing surface imaging, and thermal infrared (IR) monitoring to evaluate early indicators of failure. Results demonstrate that substantial subsurface erosion and channel development occurred without measurable surface deformation until the moment of breakthrough. While surface imaging detected no precursory settlement, pore pressure transducers recorded subtle but identifiable total head changes following defect exposure. Sensors located within one culvert diameter of the defect captured measurable head reductions as erosion progressed, whereas sensors positioned farther away showed minimal response. These findings indicate that subsurface instrumentation can detect hydraulic changes not observable through visual inspection; however, the measured pore pressure variations were small and highly localized, underscoring that conventional piezometers provide point measurements whose effectiveness depends strongly on proximity to active erosion zones. Thermal IR imaging successfully identified preferential seepage pathways not visible in RGB imagery, demonstrating its potential as a complementary monitoring tool. Overall, the experiments show that internal erosion can progress undetected at the surface and that strategically placed subsurface instrumentation provides valuable early-warning information. To improve detection reliability in practice, future levee monitoring efforts should consider distributed sensing technologies, such as fibre optic or high-resolution sensor arrays, to enhance spatial coverage and increase the likelihood of identifying localized erosion prior to surface manifestation.