By rosebell
Following a peer review by tunneling and transit experts from major transit agencies, a large single bore was confirmed as the preferred option for BART Silicon Valley Phase II by Santa Clara Valley Transportation Authority (VTA).
In order to advancing the largest public infrastructure project in Santa Clara County, the VTA board heard a presentation on the peer review and its recommendations and the discussion’s result was that the board voted in favour of the single bore as the most viable option, offering the best balance of constructability, feasibility, and lower overall risk.
The advantages of this single bore is preventing the high cost, complexity, and downtown disruption associated with an alternative concurrent tunneling approach using two TBMs, as VTA says, whereas this would have required a cut-and-cover excavation in the heart of San Jose.
The decision allows VTA to advance project design towards 60%, stay on a critical path to tunnel construction, and meet the projected revenue service date.
Additionally, recommendations to ensure greater cost estimation, accuracy and budget alignment, reduce schedule delays and manage tunnel risk, are the contents of this panel.
Considering that now the owner TBM is VTA, it assumes full responsibility for its performance and with the aim of managing this risk, it is due to deploy a top-tier tunneling team and embed Herrenknecht engineers to support operations and reduce delays.
For progressing the large diameter tunneling, the panel also highlighted the limited pool of qualified contractors and skilled labour. In order to securing experienced construction teams and developing a contract strategy toincreasebidder participation, VTA says it is going to continue early engagement with the industry.
The peer review also reinforces the importance of a strong VTA-BART partnership. Both agencies have agreed to prioritise communications.
After that the joint venture submitted cost proposals that significantly exceeded project budget limits, the board agreed to drop Kiewit Shea Traylor JV as the tunnel contractor in June, while the project’s Herrenknect EPM TBM passed its factory acceptance test ate the same month.
Linking Berryessa/North San José Station through downtown San Jose to the city of Santa Clara, VTA’s BART Silicon Valley Phase II Extension is a 10km project with four-station addition to BART and involves almost 8km of subway, with underground station platforms at 28th Street/Little Portugal, Downtown San Jose, and Diridon stations, and a ground-level station in Santa Clara. A train maintenance and storage facility will be co-located in San Jose and Santa Clara.
