Offshore structure for deltaic substrates

A marine vessel (10) adapted to be fixedly anchored on the floor of a body of water, which floor is characterized by an unconsolidated substrate, said vessel having a controlled buoyancy hull (11), a superstructure extending upwardly from said hull and including upstanding support columns (14, 16 and 17) adapted to support a deck (13) above and spaced from said hull,

• at least one foundation leg (21) guidably positioned within a support column of said superstructure, said leg being adapted for longitudinal movement within said column whereby to be controllably retracted upwardly into said hull or extended downwardly therefrom to enter the substrate beneath said hull,
• said foundation leg comprising an elongated cylindrical member defining an internal compartment (23) having an access opening at the lower end thereof, and having substantially liquid tight walls,
• a jetting system carried on said marine vessel including conduit means having one end communicated with a pressurized source of a jetting fluid, and having discharge apertures (27) at the other end thereof disposed about said access opening for directing high pressure streams of jetting fluid into the substrate beneath the foundation leg as the latter is lowered into said substrate and elongated conduit (37) extending downwardly through said foundation leg and terminating adjacent to said access opening (24) for removing substrate which has been fluidized, from said internal compartment.