Vertical capacity of grillage foundations in sand

Grillage foundations may be chosen as an alternative to standard shallow offshore foundations owing to their improved hydrodynamic performance during installation. They consist of a mesh of vertical grilles that penetrate the seabed. During vertical loading, the capacity of a conventional surface foundation may be obtained from grillage foundations if sufficient penetration is permissible. In this paper, a series of laboratory tests is reported to investigate the performance of grillage foundations in sand with different spacing, grille thickness, and numbers of grilles. The load-displacement results are examined in detail and compared with a previously proposed analytical solution. It is shown that the analytical solution captures the key aspects of the foundation's performance if minor improvements are made to the analysis. It is proposed that the improved analytical solution may form the basis of future design. In addition, intergrille plugging behaviour similar to that observed for open-ended piles has been examined photographically. Key words: footings-foundations, offshore engineering, laboratory testing, sand. Des fondations en grillage peuvent etre selectionnees comme alternative aux fondations en mer peu profonde typiques, en raison de leur meilleure performance hydrodynamique lors de l'installation. Ces fondations consistent en un grillage vertical penetrant le fond marin. Avec suffisamment de penetration, les fondations en grillage peuvent atteindre la capacite en chargement vertical des fondations de surface conventionnelles. Dans cet article, les resultats d'une serie d'essais en laboratoire sont presentes. L'etude visait a evaluer la performance de fondations en grillage dans du sable en variant l'espacement, l'epaisseur des grilles et le nombre de grilles. Les resultats en termes de charge-deplacement sont examines en details et compares a une solution analytique proposee precedemment. Il est demontre que la solution analytique reproduit les aspects cles de la performance de la fondation suite a des ajustements mineurs effectues sur l'analyse. Il est suggere d'utiliser la solution analytique amelioree comme base pour les conceptions futures. De plus, le colmatage inter-grille, similaire au comportement observe pour des pieux a bout ouvert, a ete examine a l'aide de photographies. Mots-cles : semelles-fondations, ingenierie en mer, essai en laboratoire, sable. [Traduit par la Redaction]
Introduction Shallow foundations are popular for installing offshore infrastructure on the seabed. Bransby et al. (2011) recently described a novel type of shallow foundation--a grillage--that may offer substantial benefits for [...]