Flexible form member and method of forming through hole by means of the form member

A method of forming a through hole by means of a flexible form member comprising steps of;

• placing a flexible form member at a predetermined position between an outer form and an inner form which are for shutting concrete flow off, the flexible form member comprising a hollow-shaped flexible body having an openable fluid introducing and discharging means for permitting fluid to be introduced into and discharged from the body, and a detachable cover, said cover having an outer surface and a plurality of connecting elements on its outer surface to connect a fixing member for securing itself, and being contracted by discharging fluid from the body,
• placing the contracted flexible form member within the detachable cover,
• introducing the fluid into the body of the flexible form member through the openable fluid introducing and discharging means,
• interposing the flexible form member between the inner form and outer form by expanding the body,
• pouring concrete into a space between the outer form and the inner form,
• removing the inner and outer forms after the curing of concrete,
• discharging the fluid out of the body through the openable fluid introducing and discharging means so as to contract the flexible form member, and
• removing the flexible form member out of the detachable cover and the cured concrete.