PURPOSE: To assure couplement against impact by a method in which anchor bolts fixed to old concrete are inserted into the fitting holes of the leg plates of protective liners arranged and cement mortar is injected into the holes of the protective liners.

CONSTITUTION: An angular plate 11 having an injection hole 14 and an air hole 15 is connected with a leg plate 13 having fitting holes 16 by connectors 12 and cast with a wear-resistant metal integrally to form a protective liner 1. Only a desired thick portion is cut off from the old concrete C of waterway, anchor bolts 3 are set in given places of the surface, and primary concrete 4 is placed to bury halflength of the bolts 3 and cured. The bolts 3 are inserted into the fitting holes 16 of the leg plate 13 of the liner 1 to adjust the height of the liner 1 by nuts. Secondary concrete is injected into the hole 14 of the liner 1 and the hole 14 is closed with a cover. Slackening and falling-down of the protective liner by impact can thus be prevented.