PURPOSE: To secure the stability of steel-plate shell as well as to raise the workability and economy of the shell without disturbing the surrounding ground by a method in which an air supply pipe serving in combination as an excavating compartment and a vertical rib is provided between the steel plate sheet body and the inner wall.

CONSTITUTION: A vertical rib 2, a side rib 3, and a vertical rib 2' with an air supply pipe 6 are welded to the cylindrical steel plate of a steel plate shell 1. A cylindrical inner wall 4 lower than the shell 1 is provided in contact with the rib 2 inside the lower part to form compartments 5. A band steel plate 10 having a knife-shaped tip is welded to the lower end of the shell 1. Air is supplied through an air supply pipe 6 from an air compressor and jetted from the lower end to generate a gas-liquid mixed stream in the compartments 5 to disturb the soil particles of the bottom ground under water. The solid-gas- liquid mixed stream so formed is sent out and the penetrating resistance is removed to settle the shell 1 down.