PURPOSE: To reduce the number of guide piles, and save a construction term and cost, and execute work efficiently by spraying arched excavated surfaces between the guide piles embedded into ground, formed to be excavated in a state recessed to a natural ground side, with solidifying material.

CONSTITUTION: Guide piles 1 consisting of H-shape steels and the like along a designed sheathing line are embedded into ground at specified intervals in the plumb direction, and after that, along the designed sheathing line, surfaces to be excavated between the respective guide piles 1 are excavated in a state recessed in the shapes of arches to a natural ground side, and arched excavated surfaces 2 are formed. After that, along with the progress of excavation, the arched excavated surfaces 2 are sprayed with the solidifying material 3 of the great compressive strength of concrete or the like in a required thickness. Then, a fulcrum reaction force V, a horizontal reaction force H, and an arch axial-force N are transmitted to the guide piles 1 through arch rings 4 on a natural-ground rear-side surface and the solidifying material 5, and a bearing force is increased with arch working by using the timbering effect of the natural ground itself and loading earth pressure, and distances between the guide piles 1 are contrived to be made long.