Seepage failure of sand behind sheet piles - The mechanism and practical approach to analyze

Abstract

A test apparatus was designed for studying seepage failure of soil behind sheet piles, and the mechanism of seepage failure was described through experiments on sand models with Dr≈50%. Sand models are in a stable state at an early stage of a small hydraulic head difference H between up- and downstream sides. The model sand is subjected to an irreversible deformation, that is to say, upstream subsidence and downstream rise near sheet piles after the hydraulic head difference at deformation, Hy, is reached. It is proved that the value of Hy is effectively estimated as the hydraulic head difference at which a certain prism of soil loses the equilibrium of forces using the Prismatic failure concept. As the hydraulic head difference H increases, the sand model is subjected to large rearrangement and/or movement of sand particles rather than infinitesimal deformation of the sand. The upstream subsidence and downstream rise of the soil surface increase with the increase in H. When the hydraulic head difference at failure Hf is reached, the soil model finally collapses. The sand model has approximately 10% free board between Hy and Hfi.e. Hf-Hy=0.1×Hy. The behaviour of the soil model in this part could be a self-healing phenomenon.