In earthquake-prone San Francisco, crews are digging the city's deepest foundation piles for an 802-ft-tall office-residential tower that is on course to be the city's second-tallest structure, if only temporarily. The 55-story 181 Fremont tower, sited on land reclaimed from the San Francisco Bay after the 1906 earthquake, will be founded on 42 piers that plunge an average of 255 ft—with the deepest down 264 ft—to bedrock.
Because of the tight site, which is less than 140 ft square and bordered by other large construction sites and a preschool, crews can construct only one drilled shaft at a time. Each takes three days. "It's a tiny footprint," says John Morgan, project manager with subcontractor Malcolm Drilling. "When we bring the cages in at 70-ft lengths, they take up over half the jobsite, laid on the ground. But we know how to shuffle the pieces on the game board to make them fit." On a roomier jobsite, crews could work on multiple shafts at once, Morgan adds.