PURPOSE: To construct a foundation in sea in a short time by a method in which two cylindrical steel cells of different diameters are concentrically driven into the ground under water, the inside cell is packed with a filling material, and concrete is placed into the space between the two cells and also to the upside of the cells.

CONSTITUTION: Doubly set hollow steel plate cells 1 and 2 are driven into the ground G under water through a base ring 3 by a vibro-hammer 4, and foot protection is made. The inside steel plate cell 2 is packed with good-quality soil to secure the stability of the cell 2, a foundation pile 5 is driven between the outside and inside cells 1 and 2, the soil between the outside and inside cells is excavated to a given depth, and then leveling concrete 7 is placed under water. Iron bars are assembled under water, rising concrete 8 is placed under water, and upper concrete 10 is placed to complete the foundation concrete in the sea.