PURPOSE: To increase a surface friction force and to supplement shortage of earth loading endurance, by a method wherein soil is brought into muddy water by jetting pressurized water through a pipe onto an outer periphery of a side wall body, and after muddy water is sucked, the priphery of the side wall body is filled with concrete milk.

CONSTITUTION: Pressurized water is supplied to a pipe 2 through a pressurized water feed hose 8, and it is jetted through a perforation 3 into soil on an outer periphery of a side wall body 1 of a caisson (a) to soften soil and bring it into a muddy state. A suction pump is then connected to an upper end of a longitudinal pipe 7 to suck the muddy substance through perforations in a pipe 5 on a surface of a flection cut 4 for removal. After soil on the outer periphery of the side wall body 1 is removed, concrete milk is placed to fill the gap with the concrete milk for curing.