To easily, safely and rapidly perform corrosion prevention and protection of the splash zone of a steel sheet pile or the like by making the hole of the perforated coupler of recess type covering material communicate with the hole of a perforated coupler provided in a structure to overlap both perforated couplers and inserting the insertion bonding material into the communicating holes to fit the covering material to the structure and providing a hardening raw material between the structure and the covering material and hardening it to integrate two sides.

Perforated couplers 5 provided with holes 4 are welded and fitted at two lines in the longitudinal direction in the prescribed position on the land side of continuously driven recess type steel sheet pile 1A. Then, in the recess type covering material 9, perforated couplers 8 are projected in the positions corresponding to the perforated couplers 5 fitted to the recess type steel sheet piles 1A. The holes 10 provided in the perforated couplers 8 are made to communicate with the holes 4 of the perforated couplers 5 to overlap the perforated couplers 8 on the perforated couplers 5. The recess type covering material 9 is fitted to the recess type steel sheet piles 1A by inserting the insertion bonding material 11 into the holes 10, 4. In this manner, the recess type covering material 9 is fitted on the land side of the continued steel sheet piles 1A and the projected type covering material 9A is successively fitted on the sea side. A hardening raw material is poured in the interval of the recess type steel sheet piles 1A and both covering materials 9, 9A.