Abstract: An apparatus and method for installing a deck on an offshore substructure is provided. The apparatus comprises a deck supported by lifting mechanisms that are in turn attached to pontoons. The apparatus floats on the water with the lifting mechanisms compressed until transported to an offshore substructure having an upper end located above the water surface. The lifting mechanisms are then extended and the apparatus moved on the surface of the water to position the deck over the substructure. The deck is then lowered onto the substructure and the pontoons are lifted out of the water.

Abstract: An offshore structure which is resistant to wave, earthquake and ice loads and can be quickly installed and abandoned in response to changing environmental conditions includes a caisson having an upper section and a lower foundation section which are separated by a structural diaphragm. When installed, the lower foundation section extends downwardly a distance from the seafloor to provide sufficient lateral and vertical soil resistance to resist lateral and vertical loads on the structure. The upper section is adapted to support a deck structure. The structural diaphragm is adapted to rest on the seafloor when an offshore structure has been fully installed to enhance the lateral and vertical load carrying capacity of the offshore structure. During installation, the structural diaphragm and a pump are used to form suction in the lower foundation section, thus enhancing the penetration of the lower foundation section into the seafloor.