Building 391 was constructed in 1973, and has one basement level and two levels above. The project location was on the basement floor which has vehicle and pedestrian access from the north side of the building. Below the basement floor is a 30-foot diameter concrete pit. The pit floor is approximately 37 feet below the basement floor. The basement floor itself is approximately five feet thick. There are two openings in the basement floor above the pit. A scaffold stair accessed the pit floor through one opening. The other opening is an eight-foot diameter hole. An existing gantry crane located at the top of the basement floor’s 40-foot high expanse was utilized to move construction materials in and out of the pit through this hole.
Cerrudo grouted an existing 15-foot diameter, 3” deep depression in the pit floor with self-leveling mortar. Scaffolding was constructed in the basement floor plenum to provide access to the existing fire riser connection. The fire protection piping was extended from this point down and around the basement wall, and through a small opening in the floor to the pit. Low conductivity supply and return piping, compressed air piping and electrical conduits were extended from the basement floor down into the pit. New electrical panels, disconnect switches and lighting were installed. A sump pump including holding tank, control panel, disconnect switch, float switch and associated piping was installed in the pit.
The existing scaffold stair was removed and a new metal spiral stair, furnished in four sections, was lowered through the stair opening into the pit with the gantry crane, and bolted together and to the concrete pit wall. Aluminum plates, 4 foot by 8 foot, were lowered to the pit floor and secured to the floor with flush anchors.