Failure Patterns of Protective Flexible Mattresses on a Riverbank under Water Flow Scouring. II: Multistage Identification and Quantification

Analyzing and quantifying failure patterns of bank protective flexible mattresses are of the paramount importance in bank stability assessments and early collapse warnings. Based on the experimental results presented in the prior companion paper, this paper focuses on the identification of failure patterns and their stages. A step-like deformation pattern is revealed, and a three-stage process of deformation and failure is delineated. The paper introduces a 3δ criterion for identifying the timing of sliding collapses and a quantitative method for failure classification. Based on these results, a discriminant method for assessment of a state of the riverbank protected by a flexible mattress is proposed. It can be applied in practical engineering projects using topography data and a proposed optical sensing with the U-shaped layout. The paper provides new quantitative data and physical insights into the coupled bank-mattress failure patterns and deformation stages, informing quantitative categorization of bank toe collapse and risk assessment.