PURPOSE:To increase resistance to unbalanced earth pressure and lessen the amount of back-filling soil by a method in which excavated soil and sand are stored, reinforced concrete segment is used as a sheathing material for excavated pit, and the excavated soil and sand are back-filled in space within the foundation. CONSTITUTION:The sheathing work for the inner wall of an excavated pit is constituted by a reinforced concrete segment 1 and a steel key segment 5 into a circular wall form. And, a rod 7 is pierced through the segement 1 and hung down, and the lower part of the circular wall is excavated. The excavated soil and sand are stored in a temporary yard. Then, the next segment is placed on an assembler 11 and connected with the next circular wall by means of a rod 7 and a coupler 8 in the lower part of the previously assembled circular wall. The operations are repeated until a given depth is reached. The bottom part is excavated in a wider range toward the outside, an expanded bottom segment 9 is assembled, a bottom floor plate 10 is attached to the inside, and grout is injected. And, the excavated soil and sand R are back-filled in the inside of the foundation.
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