PURPOSE: To remove extra-banking concrete for a cast-in-place pile simply by the use of a bucket by substituting the extra-banking concrete with foaming mortar.

CONSTITUTION: Earth and sand 9 is excavated and filled with a bentonite mud making liquid 11, and a mild steel bar cage 10 is inserted after excavation, and a curing cover 12 is installed, and concrete 3 is placed bit by bit using a tremie pipe 6. Further thereupon an extra-banking concrete is placed and is sucked off by a vacuum pump 18 till a specified position. A great major part of aggregate is separated away by a vibratory screening machine, and a foaming agent is added so that a foaming mortar 8 is prepared, with which a casing pipe 2 is filled to the top, which is then drawn off, and after construction of cast-in-place pile, the foaming mortar 8 is removed by a bucket while the peripheral part is left. The remaining mortar 8 and a curing cover 12 are removed while excavation of earth and sand 9 is continued to the specified position.