6 b will not bend due to this characteristic in the pile assembly 1 of the present embodiment 4 guide rails 4 are fixed at once to the precise desired position on the inner wall of the steel pipe using the above mentioned magnet cross gauge 40 on the other hand since the guide grooves 6 d are formed on the movable base member 6 c of the core assembly 6 to be mounted within the pile assembly 1 by retaining the guide rails 4 therein it is possible to reduce the time consumed in the conventional assembling process which was extremely difficult hence works previously required a pair of workmen are simplified to works requiring only 1 further with the wedge members 6 a 6 b projected and rooted from the pile assembly 1 the sidewall of pile assembly 1 is supported by a plurality of the wedge members 6 a 6 b as the pointed leading member 5 is supported by the spiral blades from such feature the pile assembly 1 is maintained in a state strongly rooted within the earth further the pile assembly 1 of the present embodiment has a simpler composition than the above mentioned pile assembly 1 of the first embodiment in the pile assembly 1 of the first embodiment the wedge members 6 a 6 b have to bend in order to be projected out of the pile assembly 1 whereas in the pile assembly 1 of the present embodiment the wedge members 6 a 6.