600 7th Street

Drill Tech was contracted to provide deep foundation support along a busy street in downtown San Francisco; our teams planned a two-phase construction method to meet the owner’s needs. The project engineers designed stone columns to mitigate liquefication and lateral spreading through densification, which would be followed by torque down piles for the necessary deep foundation elements. The project was limited by a very tight schedule, owner funding challengers, and access restrictions. Despite these difficulties, Drill Tech completed construction a week ahead of schedule. This was in no small part due to the on-site field staff, who coordinated deliveries of stone, pipes, concrete, and Drill Tech’s earth-work trade partner through the 200-foot jobsite’s single gate.

The urban environment of the project required noise and vibration sensitivity measures, which Drill Tech accomplished by using a non-vibratory installation method when drilling the project’s stone columns. Our teams installed approximately 900 columns spaced six feet apart in a hexagonal pattern. Torque down piles constituted the necessary deep foundation support and used the newly densified soil for lateral support to carry the building loads. Each torque down pile measured up to 150 feet long and reached far beneath the site’s soft clay to reach a bearing layer that could support the axial loads. Finally, the torque down piles were tested for strength, in excess of 600 kips, and proved sufficient for the project.