Bay Corridor Program

Bay Corridor Phase 2 – North (Design-Build)

Mitchell Engineering managed this design-build project for the San Francisco Public Utilities Commission in San Francisco, CA. The project involved design, engineering, permitting, labor and materials procurement, construction, and testing of three main aspects. These included a new underground electrical duct bank system with electrical and communication vaults, a new Auxiliary Water System Supply (AWSS) ductile iron pipe, and road and sidewalk restoration.

The project was divided into two Segments. Segment 1 took place on Terry A Francois Blvd between South Street and Mission Rock Street, while Segment 2 was on Illinois Street between 23rd Street and Marin Street.

Mitchell’s experience working in San Francisco and their involvement in the design process contributed to the successful construction at these two locations. In total, about 820 feet of 2-inch conduit, 2.2 miles of 4-inch conduit, and approximately 9 miles of 6-inch conduit were installed. Additionally, 2 existing electrical vaults were relocated, along with 8 communication vaults, 7 equipment vaults (8′ x 16′ x 8′), and 2 large electrical distribution vaults (11′ x 28′ x 10′ – constructed in 5 pieces) in these heavily traveled areas. The Terry A Francois location also required 1,550 LF of 20” Earthquake Resistant Ductile Iron Pipe (ERDIP) for the City’s AWSS and 250 LF of 8” DIP for hydrants. Both locations also involved streetscape work such as sidewalk reconstruction, street paving, landscaping, isolation gate valves, hydrants, pipe laterals, and appurtenances.

The original project concept included designing and constructing two 54” diameter 23’ deep tunnels under SFMTA light rail tracks near the Muni Metro East Facility along Illinois Street. Mitchell took advantage of an opportunity during a Facility shutdown to propose an open cut design under the tracks leading to the facility, which ultimately saved time and money for the project.

Bay Corridor Phase 3 Electrical Substation (Design-Build – Civil Subcontractor)

This project involved the design, engineering, permitting, labor and procurement of materials, construct, deliver, install, test, and commission a high voltage electrical 230/12.47kV gas-insulated substation system along with all integral components for a fully functioning substation.

As the primary Civil Contractor, Mitchell provided civil engineering design review and construction for site earthwork and excavation, 12,249 LF of 14″ precast concrete pile installation, approximately 850 CY of structural concrete placement for vaults and foundations housing GIS equipment, switchgear, cable vault, secondary equipment, fire barrier walls, oil containment walls, and two transformer pedestals (mass concrete). In addition, Mitchell constructed 12-foot-high precast panel perimeter walls. Outside of the substation work, Mitchell conducted the construction of new sewer lines (over 600 feet) and water lines (over 1,000 feet), as well as landscaping and, improvements to Davidson and Rankin Streets.

Mitchell also provided support for pulling new 230 kV and 15 kV power conductors, and fiber optic cables through the existing underground conduit infrastructure, connecting PG&E Potrero Substation and the new substation, and from the substation to customers, as part of other Bay Corridor Transmission and Distribution contracts.