PURPOSE: To sink a side wall structure horizontally by jetting a high-pressure water at the lower end of the side wall structure in the settlement work of a large-size structure.

CONSTITUTION: A pointed portion 1 is provided at the lower end of the periphery of the lowest part 5 of a structure and its back side is covered with a steel plate cover 2. A high-pressure water is jetted from nozzle 4 at the lower part of the structure to remove soil and sand in and around the lower part of the structure. And, the void between the lower end of the structure and the soil and layer around it and the quality and strength of the soli and sand layer are detected by a detector 10 at the lower end of the structure, the pressure and amount of water jetted from the nozzle 4 are regulated, and the amount of soil and sand removed from the lower part portion of the structure is controlled under almost the same condition to sink the structure horizontally.