BART Transbay Tube Geotechnical Investigation

San Francisco, California


Bay Area Rapid Transit

Warren George, Inc.


This challenging project required marine borings to depths of 500 feet and was completed 1 month ahead of schedule and 4 percent under budget.

Twenty six borings were made to investigate the properties of the granular backfill and soft marine deposits that surround the Transbay tube as part of BART’s seismic upgrade program. The borings extended to a maximum depth of 500 feet. Twenty four of the borings were drilled from a barge in San Francisco Bay.
Warren George, Inc. of Jersey City, NJ, was awarded the contract for geotechnical drilling and field testing and named Robert Kirby of TERRA as their Authorized Representative to BART.
In his role as the Contractor’s Representative, Mr. Kirby developed the work plans and schedules, monitored project progress and reported it to BART at weekly progress meetings, and produced the project progress reports that summarized all the data collected on the project.
The project included a variety of state of the art field sampling and testing methods:

  • Energy measurements on Standard Penetration Tests and Large Diameter Penetration Tests;
  • Cone penetrometer tests using the memocone, a self-contained wireless cone penetrometer;
  • Undisturbed samples of soft San Francisco Bay Mud were obtained using the Gregory sampler, an improved version of the traditional Osterberg Sampler developed by Warren George;
  • In-situ field vane tests were made to evaluate the shear strength of the soft San Francisco Bay Mud; and
  • The deep boreholes were geophysically logged using downhole suspension logging equipment.

The work on the project was finished 30 days ahead of the contract required completion date and the actual cost of the project was 4% below the bid amount.

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