Effects of scour on the bearing capacity of flexible pile in clay: An analytical approach

Scour is closely associated with a considerable number of pile foundation instability incidents in water environments. Previous research proposed various failure modes of soils surrounding flexible piles in clay for predicting the lateral bearing capacity, while the scour effects have not yet been well investigated. This study proposes three distinct three-dimensional upper-bound collapse mechanisms: meniscus-conical wedge, full flow, and transition planes, aiming to predict the bearing capacity of scoured flexible pile in clay. The energy dissipation caused by abrupt transitions in velocity at the upper and bottom surfaces is incorporated to ensure compliance with the kinematically admissible velocity field. Within the framework of plasticity theory, rigorous upper-bound solutions are derived in closed form. Criteria for identifying three failure modes are established by wedge failure range and scour hole dimensions. The reliability of derived solutions is substantiated through comparing with the results of centrifugal tests, FEM and existing literature. Additionally, a thorough parametric study is performed to well understand the influence of scour hole size, adhesion factor and stress history on pile bearing capacity and the internal mechanism of wedge transition to full-flow. Research findings of this study aid to guide the design and maintenance of piles in marine environments.