A system for constructing a support column includes a mandrel with an upper portion and a tamper head. A feed tube extends through the mandrel for feeding flowable material to the head. The tamper head includes a lower enlarged chamber with a reducing surface at an upper portion and includes a plurality of chain links for compacting material and restricting upward flow of aggregate. The tamper head is of a size providing an enclosed region for allowing cementitious materials to be placed therein. A non-moveable sealed top plate and a separate flowable material supply tube is included via a sealed connection. A pressure gauge for monitoring air pressure within the tube portion is included and allows a support column including a cementitious inclusion on top of an expanded base to be built with a known unitary expanded base volume calculated based on pressure drop indications.