Suction caisson installation in sand with isotropic permeability varying with depth: Fid-Bau Portal

Suction caisson installation in sand with isotropic permeability varying with depth

Harireche, Ouahid / Mehravar, Moura / Alani, Amir M.

Abstract Suction-induced seepage is pivotal to the installation of caisson foundations in sand. Indeed, the upward pore water flow on the inner side of the caisson wall causes a release of a fraction of soil resistance due to the reduction of the lateral effective stress. A safe caisson installation requires a reliable prediction of soil conditions, especially soil resistance and critical suction for piping. These soil conditions must be predicted for the whole installation process. In this paper, we examine the effect on such prediction of the assumed permeability profile, which is described as a function of depth below the mudline. This study is motivated by the fact that marine sediments generally exhibit a permeability that decreases with depth because of consolidation under gravity. Hence, the question is whether conventional theories based on a constant permeability lead to a conservative prediction of soil conditions or not. Our conclusion is affirmative only regarding piping condition. As for soil resistance, a prediction based on the assumption of a constant permeability is non-conservative. This is due to an overestimated reduction in effective stresses under suction-induced seepage.

Highlights • Numerical modelling of the normalised seepage problem around a caisson foundation in sand. • Effects of suction-induced seepage on soil resistance against caisson penetration in sand. • Critical soil conditions during caisson installation. • Seabed with various profiles of permeability decreasing with depth.