Seepage induced displacements of suction caissons: FE analysis

Abstract

Finite element analyses of suction caissons are performed under seepage flow in elastic soil. Poroelastic water elements are used underneath the caisson lid allowing for modelling of suction and inducing seepage flow into the caisson compartment. A detailed parametric study is undertaken exploring the effects of caisson aspect ratio, soil-caisson interface roughness, caisson inner ring stiffeners, and potential gap formation between caisson outer wall and soil, and soil permeability on caisson upward displacement. The results indicate that caisson roughness and stiffeners affect caisson displacement behaviour. A rough caisson causes earlier dissipation of suction hence caisson upward displacements are minimal for a rough caisson compared to a smooth caisson. A steady state seepage condition is only achieved for a smooth caisson with no stiffeners. Presence of stiffeners and surface roughness leads to a halt in caisson upward displacement. Any potential gap along the outer skirt interface enhances the upward displacement for a smooth non-stiffened caisson, but not for a caisson with stiffeners or a rough caisson. For the smooth non-stiffened caissons, unified equations are proposed to estimate seepage length and caisson displacement for soils with different permeabilities.