Millennium Tower, 301 Mission Street
Millennium Tower, 301 Mission Street
Millennium Tower, 301 Mission Street

With bedrock more than 200 ft below street level, the fifty-eight-story Millennium Tower, like most downtown high-rises, is founded on piles driven through soft, compressible clay soils deposited by the San Francisco Bay and extending into a dense sand layer overlying ancient marine deposits of clays, silts, and sands. Consolidation and lateral displacement of the soils under the building’s weight and adjacent construction activity caused the tower to settle more than 17 in. and tilt 4 in. across its footprint, concerning the condominium owners and City of San Francisco. SGH assessed the effects of this movement on the building’s stability and earthquake resistance, and designed an upgrade to arrest further settlement and reverse much of the tilting.