Rethink of the BART to San Jose configuration 07 May 2020

Shani Wallis, TunnelTalk

Extension of the BART heavy rail system to Silicon Valley in the San Francisco Bay Area region of Northern California, through the city of San Jose, is undergoing another configuration rethink. The larger single-bore tunnel with center platform stations in the bored diameter and the trackway side-by-side throughout, is no longer in contention, and the smaller diameter single-bore concept, with stacked station platforms, is back in play.

The smaller diameter single-bore concept with stacked platforms in the bored diameter at stations received environmental clearance, but the fact that the owner and future operator are different entities adds some complexity. BART requested VTA explore a different side-by-side track configuration within the single-bore tunnel. The VTA, Valley Transportation Authority, will fund, design, build and own the infrastructure, and BART will operate the transit service. BART raised some previous operational concerns regarding the ventilation design, uncustomary train operations and emergency egress.

Considered reconfigurations of the extension design
Considered reconfigurations of the extension design

The other consideration is an undertaking by VTA to limit construction disruption, particularly as the route runs under Santa Clara Street at the heart of retail, business and residential in downtown San Jose. Of the 6-mile (10km) Silicon Valley BART extension by VTA to Santa Clara County, 5 miles (8km) runs underground beneath San Jose with four stations, three underground and one at grade (Fig 1).

Following several months of evaluating different configurations within a single-bore tunnel, BART agreed to a large single-bore concept with side-by-side tracks and a 24ft (7.3m) wide center platform at each of the underground stations. In July 2019, VTA began advancing the larger single-bore design with its Program Management Team (Joint Venture between HNTB and WSP) and its General Engineering Consultant MMW (Joint Venture between Mott MacDonald and PGH Wong Engineering).

In December 2019, the 10% design by MMW for this configuration included a tunnel of about 49.5ft (15.1) i.d. and would require a TBM of 56ft or 17m o.d.. As design progressed, higher projected risks were identified, and preliminary cost estimates exceeded funding available. At a VTA industry forum, feedback from tunneling contractors also indicated that the higher risks may reduce the interest in bidding for the project and possibly increasing the cost of the prospective bids. Due to the higher projected costs and increased associated risks, it was determined all previous options needed to be re-evaluated.

An evaluation process revisited the larger single-bore tunnel, twin running tunnels of about 6m i.d. between cut-and-cover stations, and a stacked single-bore diameter tunnel of about 43ft (13.1m) i.d., including stacked station platforms in the tunnel. Due to the higher costs and associated risks for the larger diameter bore tunnel and due to the construction impacts associated with the twin bore concept, VTA is no longer pursuing these options. Within the options twin or single tube trackway tunnels between mined stations excavated using SEM sequential excavation methods have been considered but dismissed as high risk in the saturated sandy soils of the area, under a high groundwater table.

Having previously had reservations with the stacked single-bore concept, BART has agreed to an optimized, stacked platform single-bore concept with enhanced emergency egress at the two mid-tunnel ventilation structures. From the western enhanced mid-tunnel facility west, the larger single-bore diameter will accommodate side-by-side trackways to the west portal. East of the eastern enhanced mid-tunnel facility, and through a cut-and-cover station at 28th Street/Little Portugal Station, the trackways are required to be side-by-side. Only the central section between the mid-tunnel facilities will contain stacked tracks.

Managing the variables, to provide leadership, oversight and accountability in the management and delivery of the BART Silicon Valley Program is now the task of Takis Salpeas who joined VTA in February. Within his 35 years of experience, Salpeas worked for the Washington DC WMATA Transit Authority, the Los Angeles Metro, and for BART, to manage its San Francisco Airport extension.

Under the Salpeas leadership, VTA will advance design on an optimized single bore, stacked platform configuration and assess any environmental, right of way and utility considerations. VTA will also be preparing documents to submit for the FTA Expedited Project Delivery Pilot Funding Program.

In the meantime, the first 10 miles of the BART system to Silicon Valley, known as the Phase I Berryessa Extension Project, has been in construction for the past eight years. Aligned mainly at grade, the project has transitioned from a VTA construction project to pre-passenger testing and operations by BART. Passenger services are planned to begin summer 2020.

The two separate authorities are involved in the extension project because Santa Clara County opted out of becoming part of the BART Bay Area Rapid Transit District when first formed in the 1960s and County residents did not contribute tax revenues to previously support the system. VTA therefore secured the funding to build the extension and will manage construction infrastructure for the extension of BART to San Jose and Santa Clara with services on the extension to be operated by BART. Current estimate for Phase 2 extension is currently estimated at about US$6 billion.


Funding and single-bore secured for BART to San Jose 03 May 2018

Shani Wallis, TunnelTalk

The single-bore option has been approved by project owners for the 5 mile (8km) extension of the BART rapid transit system to San Jose and Silicon Valley in Northern California. A TBM of about 45ft (13.7m) diameter will excavate the single-tube, double-track tunnel that will also accommodate the platforms for two of the four stations on the extension that lie beneath downtown San Jose (Fig 1).

Fig 1. BART extension to downtown San Jose
Fig 1. BART extension to downtown San Jose

At the same time, US$730 million in State funding for the project from the newly passed gas tax of the California Senate Bill 1 was also agreed by the California State Transportation Agency. The funding now supports a request for $1.5 billion in Federal Government grants including from the New Starts program, to be made this summer. The balance of funding for the $4.8 billion project will be sourced via multiple local funding vehicles including the 2000 Measure A half-cent sales tax at $1 billion, the State of California and its Traffic Congestion Relief Program (TCRP) at $160 million, the 2016 Measure B, half-cent sales tax at $1.5 billion, and a maximum of $750 million from the Transit and Intercity Rail Capital Program.

“The magnitude of these announcements, and the regional significance of the project, cannot be understated,” said VTA (Santa Clara Valley Transportation Authority) General Manager and CEO, Nuria Fernandez.

The single-bore option is adopted after a thorough review by VTA and BART in January and February 2018 and calling on industry experts for the single and twin-bore tunnel options. Promoted by consulting engineer HNTB among others, the single-bore option was approved by the VAT Board of Directors and by the BART (Bay Area Rapid Transit) Board of Directors as operator of the rail system that servers San Francisco, the Bay area cities and will run services on its extension to San Jose and Silicon Valley. VTA, the authority responsible for delivering the BART extension into downtown San Jose and Santa Clara, is preparing to provide the safest, least disruptive project of infrastructure construction to meet the needs of the operator (BART) and the expectations of community stakeholders, and ensure prudent investment of taxpayer dollars.

The single-bore design is described as meeting industry and BART facility standards for operations and safety and as minimising construction impacts of the more traditional twin-tube single track running tunnels and associated open-cut station box construction. It is also reported as expecting to shorten the four-year construction program by 10 months and reducing construction costs by about $50 million.

Compared to the twin-bore option, the single-tube option is adopted to:

  • Limit excavation within the public street right-of-way, resulting in less construction impact to businesses and the community during construction;
  • Avoid closure of Santa Clara Street and adjacent roadways in San Jose, reducing impact to traffic, cyclists, and pedestrians during construction;
  • Eliminate impact to the VTA light rail services, avoiding temporary closure of tracks crossing Santa Clara Street at 1st and 2nd streets for street-level excavation; and
  • Provide greater operational flexibility, allowing for the ability to provide multiple crossover tracks and areas to store train cars within the tunnel for emergencies, special events, or regular maintenance activities.

Construction is programmed to begin in 2019 towards completing the project and starting services in 2026. “Confirmation of these recent decisions are key milestones in our decades-long effort to bring BART all the way to Downtown San Jose and Santa Clara,” said Sam Liccardo, Mayor of San Jose and Chairperson of the VTA Board of Directors.

As a next step in project development, VTA has organised a forum for 15 May 2018 to provide information about the upcoming RFP (request for proposals) for general engineering consultants and to invite DBE (disadvantaged business enterprise) and SBE (small business enterprise) firms to participate in the project’s procurement phases. Details of the forum are announced on the TunnelTalk Procurement service.


Single bore option for BART to San Jose 01 Jun 2017

Shani Wallis and Peter Kenyon, TunnelTalk

Extension of the Bay Area Rapid Transit system, BART, to the city of San Jose on the south end of San Francisco Bay in northern California, is into perhaps its most positive stage of development and realisation. After years of stalled progress, funding sources are now identified and with a procurement programme in place, the project developers are exploring signal bore options for the underground stations and track alignment ahead of plan start of construction in 2019.

Fig 1. Details of the BART extension under San Jose
Fig 1. Details of the BART extension under San Jose

The initial plan for the 6-mile extension of BART services beneath downtown San Jose (Fig 1) was to link three underground stations with conventional twin-tube TBM-bored running tunnels. Planners of the underground alignment of the BART to San Jose metro rail extension are now exploring the single-tube, twin-track running-tunnel concept with the tunnel divided by a horizontal deck for trains to run in the upper and lower sections of the tunnel in a stacked configuration and allow the platforms at stations to be accommodated within the same single-tube, TBM-bored tunnel (Figs 2 and 3).

Known also as the Barcelona method, the concept was developed in Spain and used on the city’s Line 9 project and to positive effect. The advantages of the system are several fold. In particular, the disruption and cost of extensive open-cut excavation of stations into the streets of the city is avoided. Excavation at stations is confined or restricted to smaller off-line ingress and egress access structures to cross passage adits to the underground station platforms, stacked and aligned in the single-tube double-track tunnel. In addition, a single tube double track tunnel of approximately 12m diameter excavates less material than twin parallel single tube tunnels of 6-7m diameter each, and uses less concrete material in its precast segmental lining. The cost of one larger diameter TBM is also potentially less than the cost of two smaller diameter machines. The pros and cons of the two different methods are being considered in the current schedule of studies.

Current estimates of the (9.5km) underground Phase II Silicon Valley Extension beneath San Jose is costed by the Santa Clara Valley Transportation Authority (VTA) at US$4.7 billion. Of this, US$1.5 billion (nearly 30%) is being applied for allocation from the New Starts Program of the Federal Transit Administration (FTA). $2.5 billion will be raised via a local sales tax increase approved by Santa Clara County voters in the November 2016 ballot.

Fig 2. Single-tube, double-track, TBM tunnel with the platforms included at stations
Fig 2. Single-tube, double-track, TBM tunnel with the platforms included at stations
Fig 3.  Plan of the off-line station access structures
Fig 3. Plan of the off-line station access structures

In December 2016, a VTA spokesperson told TunnelTalk: “Based on the current schedule, construction procurement activities are planned for late 2018 with heavy construction scheduled to start by mid-2019. The format and specific procurement process is likely to be finalized in early 2018, with the evaluation of contracting strategy and packaging likely to begin in mid-2017.”

The Phase II project has provisional New Starts Project Development (NSPD) status with the FTA and design is at an advanced stage ahead of confirmation of environmental permitting and expected FFGA (full funding grant agreement) from the FTA by December 2017.

Fig 4. The extension to Silicon Valley will add another 4.5 miles of underground infrastructure to the 112-mile BART network
Fig 4. The extension to Silicon Valley will add another 4.5 miles of underground infrastructure to the 112-mile BART network

The BART to San Jose project has had a checkered history.

In 2001, VTA and the BART District entered into a comprehensive agreement to extend BART services into Santa Clara County. VTA’s BART Silicon Valley Program, is responsible for ensuring the intent of the comprehensive agreement is fulfilled. Beginning in 2002, VTA initiated planning, environmental, and conceptual engineering activities for the full 16-mile extension from the Warms Springs Station end of the East Bay alignment in Alameda County all the way to downtown San Jose and Santa Clara city (Fig 4).

In 2005, VTA initiated preliminary engineering activities followed by 65% engineering activities in 2007. By the end of 2008, VTA made the decision to deliver the program in phases. One of the major funding sources for the BART Silicon Valley Program is the sales tax measure passed by Santa Clara voters in 2000. As a result of the economic downturn in 2007/ 2008, the amount of expected revenue from the tax measure was substantially less than originally projected. As such, in 2008, the decision was taken to deliver the program in two phases.

Subsequent to this decision, design activities for Phase II were put on hold, while Phase I for the 10-mile at-grade extension from the BART Warm Springs Station in Alameda County to Berryessa Station in San Jose, continued and into construction. Phase I construction is currently ahead of schedule and the extension is expected to be open for ridership in late 2017.

Planning and environmental clearance efforts for Phase II were restarted in 2013. Current focus for the 6-mile Phase II project to extend services from the Berryessa Station underground through downtown San Jose and to surface again for an at-grade station at Santa Clara, includes the reevaluation of tunneling methodology and the tunnel alignment and stations configurations.

Operating station tunnel on the Barcelona Metro Line 9
Operating station tunnel on the Barcelona Metro Line 9

The tunnel segment of Phase II is approximately 4.5 miles long beginning at the east portal in the Alum Rock area of San Jose and concluding at the west portal adjacent to I-880, south of Avaya Stadium in San Jose. Based on the current design, tunnel excavation would be by using a pressurized closed-face TBM. VTA anticipates a decision to be made on the tunneling methodology in mid-2017 and if the single-bore tunneling methodology is adopted, preliminary studies indicate the off-street station and entrances would be cut-and-cover construction with the platform in the bored tunnel.

The Phase II project is located in the Santa Clara Valley, which extends southeastward from San Francisco Bay, and is a northwest/southeast trending valley within the Coast Ranges Geomorphic Province of Northern California. The Valley is an alluvium-filled basin located between the Santa Cruz Mountains to the southwest and the Diablo Range to the northeast and is covered by alluvial fan, levee, and active stream channel deposits with marine estuary deposits located along the bay margins. These unconsolidated deposits cover Tertiary through Cretaceous age bedrock.

Construction of the horizontal dividing deck for the twin-track rail tunnel
Construction of the horizontal dividing deck for the twin-track rail tunnel
Lower track section beneath the completed horizontal dividing deck
Lower track section beneath the completed horizontal dividing deck

The water table in the area is approximately 10ft below ground surface with the tunnel being constructed below the water table at an average depth of 40ft below ground surface to the tunnel crown. TBM operation and hyperbaric interventions are anticipated and under hydrostatic pressures of typically between 1 and 2 bar. Beneath the rivers and retaining walls, where the tunnels are at their deepest, hydrostatic pressures of between 3 and 4 bar are anticipated.

As design progresses into final stages for the project, the only threat to its construction is suggestion from the Trump administration that it will cut severely the Federal budget allocations to mass transit projects.


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