To prevent the circulation of water inside and outside a partition in a partitioned revetment at a waste landfill by performing an improvement in impermeable treatment to an accumulation layer at a lower part of a caisson and to a base of the caisson.

When installing a caisson 11 for building a marine structural body 10, in an accumulation layer 3 of the upper part of the sea bottom ground 1 an impermeable ground improvement part 4 into which a hardener or the like is mixed is built, and an excavated groove section 5 is built in a place where the caisson 11 is set up. Furthermore, after a foundation stone layer 6 is built, an asphalt mixture is poured so that spaces among the stones of the foundation stone layer are filled with a fluid to be hardened. Also by building a joint water-sealing treatment section between the caissons 11, the water is blocked in order not to be circulated inside and outside the partitioned revetment without forming a crevice between the lower part of the marine structural body and the caisson.