BP NORTHSTAR CONCRETE SPREAD FOOTINGS

摘要

BP Exploration (Alaska) Inc. constructed a drilling and production gravel island in the Beaufort Sea near Prudhoe Bay Alaska in 2000. Several heavy modules were placed on the frozen, winter-placed gravel in the summer of 2000 and in the summer of 2001. Reinforced concrete spread footings placed on the gravel with insulation directly beneath were used to support the loads. Performance of the footings has been measured continuously since installation. It was found that footings could not be placed during the month of June when surface thaw is occurring, but those placed in subsequent months have performed well. Total settlements of about 175 mm average have occurred since 2000 and the maximum differential settlement footing to footing has been 41 mm to November 2004. Settlement rates have decreased from an initial peak of 1.9 mm/day during the first 90 days of 2000, to 0.08 mm/day during the next year, to 0.03 mm/day for the remainder of the time. Footings installed in 2001 have had an average settlement rate of 0.025 mm/day overall. Settlement rates are trending to zero and shut off of settlement is likely.