Stress-dependent erosion and post-failure morphology at soil-structure interface: insights from spatially zoned dyed...

The soil-structure interface (SSI) is a highly vulnerable zone for contact erosion, yet the stress-dependent hydraulic evolution and consequential post-failure morphology remains poorly understood. This study investigates the SSI erosion mechanism under varying K0 stress levels (30-360 kPa) with a specific disposition of spatially zoned dyed soil. The results reveal that SSI erosion is formed following a particle detachment-sedimentation order and characterized as retrogressive channels with low tortuosity (< 1.2), distinct from internal matrix erosion. Increasing overburden stress significantly elevates both low and high critical hydraulic gradients (LCHG and HCHG) and prolonged the transition stage due to enhanced particle inter-locking and temporary clogging. Quantitative morphological analysis further demonstrated that the expansion of erosion channel is restricted, and the sedimentation process is suppressed under high stress levels. Based on these findings, hydraulic models are established between macroscopic erosion resistance and microscopic morphological evolution. New insights are therefore provided into the "detachment-transport-deposition" cycle, which primarily governs SSI erosion stability.