Mechanisms and Geometry of Pile Installation by Water Jet Fluidization in Fine Sand

Larissa de Brum Passini¹; Fernando Schnaid¹; Marcelo Maia Rocha¹

¹ Universidade Federal do Rio Grande do Sul

Baixar PDF doi:10.20906/CPS/CB-04-0006

Resumo

The torpedo pile is an anchoring offshore structure system widely used in Brazil in deep waters. The installation procedure consists in the release of the torpedo from a high position from the sea bottom to allow the device to reach its terminal velocity. Penetration depth is a function of kinetic energy, weight and geometry of the torpedo, seabed shear resistance and penetration angle. Since penetration in sand may not be sufficient to provide the necessary anchor bearing capacity, an alternative procedure is to combine the free-fall energy to soil fluidization. This alternative is applied in this paper by considering the use of circular, single and continuous vertical jets from the tip of model torpedo piles. The mechanism of pile installation by vertical jet fluidization in satu-rated fine sand were examined in order to define the relevant parameters controlling pile installa-tion geometry and pile depth of embedment. This technology can be applied not only at offshore conditions, but also at nearshore and onshore situations. The work describes a series of laboratory model tests with a pile installed by its dry mass, of 220 g and 400 g, in both medium and dense sands using downwardly directed vertically water jets. La-boratory tests were performed in a reduced model using tubes, with external diameter of 16.2 mm, to simulate torpedo without wings, following the law of similarity of Froude number at scale of approximately 1:67. Measurements from model tests at reduced scale indicate that the geometry of fluidized cavities is not influenced by the initial density of the sand, which was prepared at relative density of 50% and 90%, and that the perturbed zone is constraint to a distance of about 2 diameters from the pile cen-treline during pile installation, independent of the applied flow rate of 0.7×10-³, 1.0×10-³ and 1.6×10-³ m³/min. By equating gravitational and upward drag forces on sand particles through Froude number, an expression for the fluidized zone is derived, which shows to be correlated with f

Palavras-chave: Topedo Piles; Fluidization; Fine Sand