PURPOSE: To enable the construction of a permeability-retardant layer quickly and economically.

CONSTITUTION: A sheathing wall 1 is constructed in the depth where it reaches a permeable layer 4, an injection pipe 2 having a length arriving at the permeable layer 4 is penetrated along the sheathing wall 1 and, at the same time, a collection pipe 3 having a length arriving at the permeable layer 4 is penetrated to a position separated from the injection pipe 2. While discharging the chemical 6 from the injection pipe 2 into the permeable layer 4, it is absorbed with the collection pipe 3 and is impregnated thereinto, and the permeable layer 4 at where the injection pipe 2 and collection pipe 3 are located is formed into a permeability-retardant layer 7.