Flood-Induced Scour Failure Mechanisms and Multi-Level Protection of Riverside Highway Embankments: A Physical Model Study

Abstract

Scaled flume tests based on Froude similarity (λ = 1:50) were conducted to clarify the internal stress-field evolution and multi-level protection mechanisms during flood scour of riverside highway embankments. An 18-channel miniature earth-pressure system embedded along the slope, with dual-view cameras, provided synchronous acquisition. Six non-replicated tests covered three protection levels (unprotected; semi-protected with gabion and geotextile; fully protected with an additional spur dike) at three flow velocities, yielding approximately 288,000 time-series readings (about 16,000 synchronous time steps). Scour failure followed a unified four-stage evolution: flow establishment and seepage onset, scour expansion and toe instability, progressive collapse and failure surface extension, and scour-hole stabilization with residual transport. Increasing velocity accelerated failure and shifted the mode from progressive toe scour to rapid retrogressive erosion. Protection structures exerted a dual effect, delaying failure at low velocities through weight stabilization and energy dissipation but potentially intensifying local scour at high velocities through flow concentration. Using internal earth pressure and higher-order statistical moments, a preliminary criterion distinguishing surface scour from internal erosion was proposed. The weight-stabilizing effect of the gabion self-weight was quantitatively characterized. AI1-13 was identified as a candidate early-warning sensor, and a dual warning signal (rise-then-fall and skewness reversal) was observed. A tentative three-level early-warning framework is proposed. Owing to the non-replicated, reduced-scale nature of the tests, these quantitative indicators are presented as preliminary bounds rather than validated field thresholds. The findings clarify embankment protection failure mechanisms and highlight the influence of hydraulic intensity and protection configuration on scour resistance.