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Transbay Transit Center Project - Below Grade Structure

A $113 million contract to construct the below grade structural portion of the Transbay Transit Center project earned Shimmick Construction Co. the Award of Excellence on a High Hazard job.
Shimmick Construction Company
Transbay Transit Center - San Francisco


A $113 million contract to construct the below grade structural portion of the Transbay Transit Center project in San Francisco earned Shimmick Construction Company the AGC of California Safety Award of Excellence on a High Hazard Job.

The project presented numerous unique challenges for the construction team, which had to coordinate construction work up around a temporary access trestle and four levels of shoring struts. Located in the heart of downtown San Francisco, the project also required Shimmick to engage in extensive and continuous coordination with other trade contractors. Through coordination meetings, detailed work planning, and constructability reviews, the Shimmick Construction team was able to mitigate many changes to provide a successful and safe project.

The project comprises five primary elements of work: waterproofing components, mat foundation slab, structural foundation walls, and an elevated concourse deck, and vehicle/bicycle ramp. The job site spans a total of 280,000 square feet, stretching over four city blocks long and one block wide. Traversing down the center of the project is a temporary construction access trestle. The project also contains three temporary vehicle bridges for local roads feeding downtown San Francisco.

Crews faced many safety hazards and challenges, not the least of which involved construction of the mat foundation slab work supported almost exclusively by crane. Many bundles of reinforcing steel were hoisted daily on the job. The loads were hoisted from the access trestle down to the slab roughly 60 feet below, presenting one of the most dangerous hazards of the project requiring a variety of mitigation measures.

The project also contains three wall lifts, two constructed while working off a slab and one lift elevated 15 feet above the slab below. In total, there are more than 250 foundation walls equaling 111,000 square feet of formwork, which brought additional hazards and required extra safety measures and training.

Construction of the elevated concourse deck required setting deck shoring, forming the slab bottom and beams, placing reinforcing steel, installing embedded metal fabrication, and placing the concrete slab. Because the elevated concourse deck is approximately 26 feet above the mat foundation slab level, there was a constant fall hazard for crews who were performing this work, so proper fall protection equipment was critical. Once the deck has been poured and deck shoring removed, it was critical not to overload the deck and to closely follow guidelines of the engineering firm which analyzed the safe loading of the deck.

The location of the project brought numerous other logistical and site management challenges, from protecting pedestrians in the busy downtown area to coordinating with trade contractors at the same site. Shimmick’s strong safety culture and its detailed safety program ultimately ensured a safe project.