Effect of perforations on the bearing capacity of shallow foundation on clay

As a type of shallow foundation, a mudmat serves as the seabed support structure for subsea wells, pipeline manifolds, and pipeline terminations. The shallow foundations are usually designed with perforations to facilitate installation and removal, but the influence of these perforations has not been fully understood. This paper presents a method to analyze the bearing capacities of both two-dimensional (2D) and three-dimensional (3D) perforated shallow foundations using finite element analysis. The soil was idealized as a Tresca material, with the undrained strength increasing linearly with depth. The outcome indicates that perforations have nonnegligible effects on the bearing capacity of shallow foundations. The bearing capacity decreases with increasing perforation ratio, R, and the degree of reduction increases with the increase of the dimensionless ratio kB/[S.sub.uo], where k is the shear strength gradient, B is the width of the foundation, and [S.sub.uo] is the shear strength at the mudline. For 2D shallow foundations, there exists a critical perforation ratio, [R.sub.c]; when the perforation ratio is lower than the critical perforation ratio, the perforated foundation does not lose its bearing capacity. For 3D shallow foundations, the bearing capacity decreases directly with the increase of perforation ratio, R. Key words: shallow foundation, clay, finite element analysis, perforation, bearing capacity. Comme une sorte de fondation superficielle, les patins servent de structure de support du fond marin pour les puits sous-marins, les collecteurs de pipeline et les terminaisons de pipeline. Les fondations peu profondes sont habituellement concues avec des perforations pour faciliter l'installation et l'enlevement, mais l'influence de ces perforations n'a pas ete entierement comprise. Cet article presente une methode pour analyser les capacites portantes des fondations peu profondes perforees en deux dimensions (2D) et trois dimensions (3D) en utilisant l'analyse par elements finis. Le sol a ete idealise en tant que materiau Tresca, avec la resistance non drainee augmentant lineairement avec la profondeur. Le resultat indique que la perforation a des effets non negligeables sur la capacite portante des fondations peu profondes. La capacite portante diminue avec l'augmentation du taux de perforation R, et le degre de reduction augmente avec l'augmentation du rapport sans dimension kB/[S.sub.uo]. Pour les fondations superficielles 2D, il existe un taux de perforation critique R, lorsque le taux de perforation est inferieur au taux de perforation critique, les fondations perforees ne perdent pas la capacite portante. Pour les fondations superficielles 3D, la capacite portante diminue immediatement avec l'augmentation du taux de perforation R. Mots-cles : fondation superficielle, argile, analyse des elements finis, perforation, capacite portante.
1. Introduction A mudmat is a type of shallow foundation that is usually designed with perforations to facilitate installation and removal. Many existing studies have concentrated on the bearing capacity [...]