Torque Down Piles were selected to minimize the impact of construction on existing utilities on this San Francisco International Airport expansion project. 84 sixty foot long piles were installed during the evening shift due to close proximity to active terminals.

Project Conditions

Prior to construction, the site consisted of an asphalt paved taxiway. The project was immediately adjacent to the international terminal building. While no site specific boring logs were available for this project, subsurface data indicated that the site was underlain by fill, soft marine clay, and interbedded stiff clay and dense sand. The piles were designed to gain support in both friction and end bearing below the soft marine clay.

Test Pile Program

Two indicator piles were installed at the site prior to production pile installation. One pile was tested in compression, one in tension. Less resistance was observed during installation of the tension test pile; therefore, both test piles were tested to twice the design compression load to confirm the piles achieved the maximum anticipated design criteria. Load deflection curves for the two pile load tests are presented on the plot to the left.

Production Piles

During construction, piles were installed within about foot of adjacent structures. One pile was spliced during installation since it was beneath an existing overhang. Space constraints and the presence of utilities limited the production rate to less than 10 piles per day. However, when provided unobstructed access, a production rate of more than 30 piles per eight-hour shift was achieved.

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