DESCRIPTION

The LCA flow equalization tank consists of a 3 million gallon concrete flow equalization tank and pumping station. The tank is 120 ft in diameter and 36 ft in height.

CHALLENGE

The recommendation of an auger cast pile foundation raised concerns due to the presence of pinnacled limestone with numerous soil voids which could result in unacceptable settlements. The compaction grouting alternate also had considerable cost and performance uncertainty. The estimated tank liquid and floor load is 2550 psf.

SOLUTION

The best solution proved to be the Impact® Pier system. A total of 331 Grouted Displacement Impact® element were installed using a filled open mandrel pipe. Once at design depth, the grout filled mandrel pipe was charged with stone, raised three to four ft then lowered using vibration and downward hydraulic force. The open-graded stone was compacted to a one ft lift resulting in an 18-inch diameter Grouted Displacement Impact element. Tremie grout was added throughout the process to increase pier stiffness and mitigate the risk of sinkhole formation from downward migration of water through the open-graded stone.