This paper presents a footing technology that uses a novel internal jetting system to quickly install jackup footings on any type of seafloor. A universal footing consists of three parts:
a solid cone spike (to support footing on hard soils, coral or rock),
a hollow spud can (for support on soft clayey soils), and
an internal jetting system (to assist with penetration and removal on sandy/silty soils).
The footing technology is one of many technologies that are being developed at the Naval Civil Engineering Laboratory for the Navy's Advanced Cargo Transfer Facilities (ACTF) sponsored by the Naval Facilities Engineering Command.
The Navy needs a unique jackup footing that can be used to rapidly deploy shallow-water facilities on any seafloor type. That need has resulted in the development of a universal footing. The universal footing concept solves the footing installation problems when installers don't have the luxury of changing or modifying footings to accommodate the various seafloor types, or when the subsoil data at the site of interest is not available. The jackup unit consists of a platform, jackup legs with jacking mechanism and universal footings. The platform can be self-elevated to a specific height above water surface using a jacking mechanism. In order to accommodate a wide range of seafloor types (e.g., mud, clay, silt, sand, coral or rock), the platform is supported by legs equipped with universal footings (See Figure 1). The universal footing consists of a spike, a spudcan and an internal jetting system (See Figure 2). The spike is a solid cone structure designed to indent into hard sediments or rock. The spudcan is an enlarged hollow can which distributes loadings over a large soil area thus increasing bearing load capacity of the legs and reducing the leg penetration depth. The jetting system assists in burying the footing into silty and sandy seafloor and thereby by its own weight, enhances overall system stability. In addition, jetting reduces the pullout resistance of the leg/ footing system upon retrieval.
The objectives of this paper are to review the jetting mechanism, present the results of the footing jet in and pullout tests with a model footing. Emphasis will be placed on the internal jetting system and its jetting performance in beach sands.
High-pressure jetting has been used for a variety of applications including soil removal, bark cleaning, rock cutting, etc. (Ref 1). These applications utilize a pressurized fluid released from nozzles which are not in direct contact with the target materials. For a universal footing, its nozzles are fully embedded in the soil and the soils engineering properties have a great influence on jetting performance.
A literature search was made to determine if a theory or mathematical model was available to predict the jetting performance of the embedded multinozzle footing in soil. The results of this search indicated there was no "clear cut" solution with which to analyze the complex embedded-jet soil problem.
