Devices installed in storage tank excavations to prevent tanks from floating out of the ground in event of a high level of groundwater in the excavation or a high groundwater level after the installation is complete.
Anchoring usually involves attaching the tank to a concrete weight.
One common anchoring method is to install a reinforced concrete pad, from 6 to 12 inches thick, in the bottom of the tank hole. Straps connected to this pad are looped over the top of the tank. When a high water level is present in the hole, the weight of the pad, plus the weight of the backfill above the pad, helps hold the tank down and prevents it from floating.
Another form of restraint is referred to as deadman anchors. These are long, heavy beams of reinforced concrete. The beams, positioned on each side of a tank, are connected to each other with straps that extend over the top of the tank. The weight of the concrete beams, plus the weight of the backfill above the beams, will help keep the tank from floating.
Calculation of the amount of anchor weight and backfill required to keep tanks from floating requires use of detailed mathematical formulas. The procedure is further explained in the Recommended Practices for Installation of Underground Liquid Storage Systems PEI/RP100, published by the Petroleum Equipment Institute.