PURPOSE: To economically increase the earthquake proofness of the foundation ground of a petroleum tank by driving steel sheet piles close to and over the whole surrounding of the tank into the banked foundation ground.

CONSTITUTION: A round petroleum tank 50 consisting of a side plate 52, an annular plate 53 and a bottom plate 54 is installed on a banked foundation ground 51. Light-weight steel sheet piles are circularly driven to about 2.5m depth over the whole surrounding of the foundation at as near distance (at least about 60cm) as possible from the side plate 52 by a construction machine in order to increase the bearing capacity of the ground 51. A steel sheet pile 55 for reinforcement is further applied. The settlement of the tank 50 for earthquake loads can thus be greatly reduced, and breaking region of the ground 51 can also be reduced. The bearing capacity of the ground 51 for concentrated vertical loads beneath the side plate 52 can be increased by such a simple construction method.