Abstract: The present invention relates to a gravity type oceanic structure and its stable installation wherein a skirt is provided downward on the outside periphery of the lower end of the part to be settled and fixed on the sea bed. When the structure is settled on the sea bed, the skirt is pushed into the sea bed foundation to intercept penetration of sea water from the circumference into the structure, and sea water in the skirt is adequately discharged by draining means to make the internal pressure equal to the atmospheric pressure. Buoyancy is thereby eliminated so that the bottom surface of the structure is fixed firmly to the sea bed.

Abstract: This invention relates to an offshore unit structure. When the sea bottom ground on which an offshore structure is to be built is weak, in order to prevent the structure from being deformed by gravitational load of the structure or by horizontal load applied thereto, a cement type solidifying agent is impregnated into and mixed with subsoil in such weak ground to construct a unit-volume reformed ground, and a unit structure body is built upon such reformed ground. The structure according to this invention can be advantageously used for prospecting or producing oil in the sea.