Dobbins Air Force Base
Raymond Engineering-GA, Inc. was retained by Merrick to determine the cause of water infiltration in the sub-flooring of the recently constructed GAC building. Our inspection revealed that the source of the water was likely coming from the juncture of the downspout located at the corner of the building and the underground drain leader. A review of available drawings showed that the underground drain leader discharged into a concrete drop inlet.
However, these drawings showed that two underground drain leaders were supposed to discharge into a drop inlet. An examination of the drop inlet revealed the presence of only one drain line. In discussions with the building contractor, it was learned that he had received approval to move the drain line in questions approximately 10 feet, then made a T-connection of the two drain lines without increasing the line diameter at the downslope side of the connection.
Additionaly, the designer had designed the entire drainage system for the 1-hour, 25 year storm event, instead of the 1-hour, 100 year event. As a result, the drain lines were not sufficiently designed to handle even a moderate rain event, and water would build up in the lines until able to enter the building at the downspout/drain line connection. Raymond Engineering assisted the designer in developing a procedure to improve the water flows to the drop inlet.