COMPLIANCE INFO_1996-2006 - Laserfiche WebLink

Home Browse Search

Ll M"Agu== I w I M; STMI I =1 ZO IF11:1 14 High water tables or water entering tank excavation will create significant uplift or buoyant force on underground tanks. These buoyant forces can be partially overcome by the tank's weight, weight of backfill used and the amount of pavement or reinforced concrete applied over tank. When additional buoyant restraint is required, flat metal holddown straps used in conjunction with concrete deadmen or concrete holddown pads maybe used. When holddown straps are used, an inert dielectric isolation material is required to separate the tank's exterior surface from the flat metal holddown strap. This isolation material should be shipped with the holddown straps from the tank manufacturer. CAUTION: Never use steel cables or round bar as holddo strap material. This configuration of holddown will cut into Soil conditions, ground water and storm water runoff must be considered when anchoring tanks. It is the responsibility of the tank owner ort owner's 0 representative ine if mechanical anchoring is required Each jobsite has varying soil and water conditions. it is the responsibility of the tank owner and its technical representative to determine actual size and thickness of either the concrete anchor pad or concrete deadmen used ata specific jobsite. Some installations will be considered "wet hole areas" where the water table must be kept at the lowest possible level in the excavation by pumping out water with or without a well point system. Consult "filter fabric" section of these installation instructions to determine if filter fabric is necessary. In the event water is used to fill or "ballast" the tank so installation can be accomplished, the following guidelines apply: • After tank is placed in hole add enough water to sink tank. • Water level inside tank should be approximately the same level as water outside the tank. • In no event shall the water inside the tank be more than 12" above the water level outside the tank. • Backfill excavation with pea gravel or crushed stone making sure to push backfill under the bottom 120 degrees section of tank to maintain proper support of tank. Modem Welding Company publishes a guideline of holddown strap sizes based on tank's capacity and diameter. Refer to this guideline when determining number of anchor points required for concrete pad or deadmen use. Holddown straps in conjunction with backfill weight and concrete pad or deadmen design work together to overcome the buoyant force of the underground Link. Once tank and holddown straps are installed it is imperative to apply remaining compacted backfill over tank before water has a chance to enter the excavation. The holddown strap guideline is for information only. Final anchoring system should be designed by approved engineer qualified in the area of soils and structural strengths of steel and concrete. Filter Fabrics I Unstable Soil Environments When tank installations are subjected to the following conditions, filter fabric is required to prevent backfill migration. • Excavation Area is subjected to frequent ground water level changes. • Excavation is in a Tidal Area. • Excavation is in a swampy area were bog, muck, peat or where other soft expansive clay type, unstable soils are present. • Soils that have less than 750 lbs./sq.. cohesion and a ultimate bearing capacity of 3500 lbs/sq.ft. are considered unstable excavations. When filter fabric is used, clean sand is not an acceptable backfill material, only crushed rock or pea gravel maybe used. Minimum bedding depth for backfill under tank in these conditions shall be 18 ".