Failure of Roadway Subbase Induced by Overuse of Phosphogypsum

Field investigations and laboratory tests were performed to determine the cause of engineering distress due to the swelling of limestabilized and phosphogypsum- stabilized soil and subsequent cracks on a roadway in China. An exploratory pit was excavated to inspect the damage state. The thickness and water content of the subbase before and after failure were compared. Laboratory compaction and expansion tests were performed to investigate the swelling behavior and the expansion potential of both the mixture from the in- situ subbase and the newly made mixture in the laboratory. It was found that the main reason for heaving in the roadway was due to the overuse of phosphogypsum in mixture of the subbase. In addition, continuous heavy rainfalls were the triggering factor for a series of chemical reactions that occurred among the mixtures in the water-rich surroundings. These combined factors resulted in the failure of the roadway subbase. This work reveals that the dosage of phosphogypsum must be controlled in a reasonable range when it is used in roadway engineering. (C) 2019 American Society of Civil Engineers.