Method and apparatus for forming manhole bases

A method of constructing a manhole base comprising the steps of:

• a. providing a substantially level casting bed;
• b. supporting a preformed manhole barrel on said bed at a predetermined height thereabove;
• c. securing at least two pipe stubs to the barrel at selected peripheral locations thereof and at selected heights relative thereto, said pipe stubs having open interior ends;
• connecting the interior ends of selected ones of said pipe stubs with an inflatable and deflatable channel form tube by inserting opposed wing shaped ends thereof into selected interior stub ends, followed by inflating said form tube to expand the ends thereof as well as a generally cylindrical intermediate portion thereof including side portions secured outwardly thereon, with said inflated side portions of said intermediate portion forming upper vertical portions of the channel to be formed in the base to be poured;
• e. providing an outer form on said casting bed to delimit the outer periphery of said manhole base;
• f. pouring concrete within said outer form and within said barrel to a predetermined height;
• g. removing the outer form after the concrete has set;
• h. deflating said ends and said intermediate portion to collapse said side portions of the form tube away from channel side walls formed by the tube in the concrete;
• and
• i. removing said form tube from the base.