the rear end thereof is projected into a shaft the subsequent double walled pipe 11 is prepared in connection with the preceding double walled pipe 11 39 of which a part of the rear end is projected into the shaft and is disposed in such a manner that the front end plane 12b of the inner pipe 12 of the double walled pipe 11 and the back end plane 12c 39 of the inner pipe 12 39 of the double walled pipe 11 39 are coupled to each other refer to fig5 and 7 in the next step as shown in fig8 b the front end plane 12b of the inner pipe 12 of the double walled pipe 11 and the back end plane 12c 39 of the inner pipe 12 39 of the double walled pipe 11 39 which are coupled to each other are welded the state after the welding is inspected by a x ray when passing inspection the portion undergone the welding is covered with a polyethylene tube 30 incidentally as aforementioned the outside face 12a of the inner pipe 12 also including portions concealed behind the concrete 14 is covered with the polyethylene member in the next step as shown in fig8 c the grout hoses 16 of the double walled pipe 11 and the double walled pipe 11 39 each being inserted into the vinyl chloride tube 15 as shown in fig6 used for insertion of the grout hose are connected to each other incidentally with respect to a pair of grout hoses which will be finally located.