PURPOSE: To dispense with the pier pile work by installing a mounted structural base on an underground first floor skeleton constructed in advance, and concurrently progressing the secondary pit excavation, The erection of the steel frame of the ground floor, and the skeleton work of the underground stairway while the mounted structural base is used as a work stage.

CONSTITUTION: Earth retaining piles 1 and a temporary steel column 6 are constructed, then the primary pit excavation 3 is applied, an underground first floor skeleton 7 is constructed on the temporary steel column 6, and a mounted structural base 8 is installed on it as a work stage. The secondary pit excavation 9 of the underground second floor is applied. A reinforced frame 10 of the underground first floor and the ground second floor is erected, and the formwork of arrangement bars 13 of the foundation skeleton is applied on the secondary pit excavation 9. Concrete is placed to construct a foundation section skeleton 12, and an underground second floor rise skeleton 14, an underground first floor rise skeleton 15, and a ground first floor skeleton 16 are constructed.