L ocated very close to two existing tanks, the new 200-ft x 60-ft VGO tank required support to prevent the effects from overlapping stresses with the foundations of the existing tanks. Subsurface, the first 6 ft is loose to medium-dense clayey silt and silty sand fill, underlain by medium dense silty sand to 12 ft below grade, underlain by stiff to very stiff clay and sandy clay to depths of 57 ft, underlain by medium-dense sand with silt to 77 ft. Groundwater was observed at a depth of 8 to 12 ft below existing grade.
PPI prepared a detailed design submittal with calculations and shop drawings of the planned rammed aggregate piers (RAPs). PPI installed 1,321 RAP ground improvement elements at a depth of 33 ft to control settlement. It increased the shearing resistance and reduced the tank settlement by installing RAP soil reinforcement in a 5-ft grid pattern beneath the entire tank footprint.
An additional ring of confining piers was installed outside the perimeter of the new tank and between the existing tanks and new tank to create a buffer zone and help dissipate the overlapping stresses on the existing tanks. The confining piers were installed for approximately half of the perimeter of the new tank (a distance of 370 linear ft).