TRANSPORT, WATER - US | SECTOR
CALIFORNIA - BART Choice of a single bore tunnel was recently confirmed for BART Silicon Valley Phase II project by the Santa Clara Valley Transportation Authority (VTA). BART Silicon Valley Phase II Extension is a
6.25 miles (10km), four-station addition to BART, connecting Berryessa/North San José station through downtown San Jose to the city of Santa Clara. VTA’s pick of a large-diameter, single bore tunnel as
preferred option for tunnelling follows a peer review by tunnelling and transit experts from major transit agencies, following which the VTA board voted in favour of the single bore as the most viable option. The single bore solution is judged to offer the
best balance of constructability, feasibility, and lower overall risk. The VTA adds that the single bore would help to avoid the high cost, complexity, and downtown disruption associated with an alternative of concurrent tunnel boring with two TBMs. This two-TBM approach would require a cut-and-cover excavation in the heart of San Jose. The decision allows VTA to advance project design
towards 60%, keep to the critical path for the tunnel construction element of the project, and meet the revenue service date. The panel also included recommendations to ensure
greater cost estimation, accuracy and budget alignment, reduce schedule delays and manage tunnel risk. As the VTA now owns the TBM, it assumes full
responsibility for its performance. To manage this risk, VTA will deploy a top-tier tunnelling team and embed Herrenknecht engineers to support operations and reduce delays. The peer review panel highlighted the limited pool of qualified contractors and skilled labour for large diameter tunnelling. VTA says it would continue early engagement with the industry to secure experienced teams and develop a contract strategy to increase bidder participation.
OHIO - COLUMBUS Granite Construction recently completed tunnel boring with an earth pressure balance (EPB) shield on the Lower Olentangy Tunnel Project in Columbus, Ohio, being built to help to reduce combined sewer overflows into the lower portion of the Olentangy River. The TBM, ‘The Mighty Quinn’, finished 3.5 miles (5.64km) of tunnels of 13ft-diameter (4.1m) through challenging geology. The alignment was through geology comprising
sand and gravel, silty sand, cohesionless silt and clay, and a small bedrock section with boulders, cobbles, and water. The Herrenknecht EPB shield machine completed two drives and an extension for the Lower Olentangy Tunnel Project. The TBM was equipped with features including a copy cutter, anti-roll fins, an inflatable emergency seal in the tailskin, and a bentonite lubrication system. Both drives started from the same launch shaft.
After completing the south tunnel, the TBM was dismantled and returned to the launch shaft to bore
the north tunnel in the opposite direction. Logistically, this sequence required the construction teams to adapt the launch plan to accommodate the ‘figure eight’ style shaft with launch angles separated by 120°. Herrenknecht praised Granite Construction’s
“outstanding inventiveness and ingenuity” in mastering the challenge of the umbilicals and the layout of crucial launch machinery.
MICHIGAN - DETROIT The Michigan Department of Transportation (MDOT) recently issued a Request for Information (RoI) to establish the primary electrical service required for the TBM launch site for a drainage tunnel, close to the I-94 freeway. The I-94 Modernisation Segment 3 Package 1 Drainage Tunnel is being built to provide a more resilient drainage solution in the area from Burns Avenue to Barrett Avenue. The 1.1 miles-long (1.75km) soft ground drainage
tunnel will have a 14.3ft (4.4m) i.d. and an estimated 49ft-78ft (15m-24m) overburden. The design-build project also includes a launch shaft, retrieval shaft, two offline drop shafts, junction chamber, pump station, adit connections, and other associated work. The subsurface conditions anticipate the use of a
pressurised face TBM. The local utility provider, DTE Energy, supplies
three-phase 480V, 4.8kV, and 13.2kV services to customers in the Metro Detroit Area. MDOT wants to determine the power required for a three-phase 13.2kV primary service to provide sufficient electrical capacity to support surface works and TBM operations at the tunnel launch/mining site and proposed onsite step-down transformer capacities and configurations, including typical redundancy and protection schemes used for TBM power distribution.
January 2026 | 25
Left:
Tunnelling recently completed at Olentangy River, in Ohio. Photo credit: Herrenknecht / LinkedIn
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