PURPOSE: To construct a bulb pile having sufficient strength by strengthening the ground by consolidation by an air-tight annular body expandible by charging of a pressure fluid and shrinkable by decompression on the lower periphery of a tremie pipe.

CONSTITUTION: A tremie pipe 1 is inserted into a pile pit 3. The lower periphery of the tremie pipe 1 is provided with an air-tight annular body 2 made of an elastic bag. By the air-tight annular body expanded by charging of a pressure fluid, the surrounding ground is consolidated to form a spherically expanded footing on the bottom of the pit hole 3. Then, the air-tight annular body 2 is once-shrunk, an iron bar cage 5 is inserted into the pit 3, cement concrete 6 is placed through the tremie pipe 1, the air-tight annular body 2 is expanded to expand and deform the lower part of the iron bar cage 5, and thereby the concrete 6 expands to cosolidate the ground where the spherically expanded footing exists. Then, the air-tight annular body 2 shrunk, and while gradually pulling up the tremie pipe 1, concrete is placed into the pit to form a bulb pile.