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Bored Tunnel Will Save Time, Possibly Money

High-speed rail which crosses the Fazeley canal, near Birmingham
The high-speed rail system currently being developed in the United Kingdom will ultimately connect 8 of the U.K.’s largest 10 cities. The first phase will link London and Birmingham, extending approximately 230 km through tunnels and over surface tracks and viaducts, such as this one across the Fazeley canal, near Birmingham. HS2 Ltd.

The developer of a new high-speed rail system in the United Kingdom is proposing that a 9 km bored tunnel be built under Ealing and Northolt.

May 21, 2013—The United Kingdom is racing ahead with the development of a new high-speed rail (HSR) line to ease congestion—for both passenger and freight traffic—on its aging Victorian railway network. HS2 Ltd., an organization that is wholly owned by the country’s Department for Transport and is developing and promoting the country’s newest HSR, released the project’s draft environmental statement and proposed design refinements in mid-May. One of the most significant revisions to the first phase of the plan, which was initially created last year, includes the proposal that a 9 km tunnel be bored beneath the borough of Ealing and the town of Northolt in northwest London, replacing a planned at-grade stretch of the route.

HS2, Ltd., first announced last month that a study of the possibility of a tunnel under Ealing and Northolt had been undertaken at the request of local residents, the Ealing Council, and the mayor of London. The study that a bored tunnel would not only minimize disruption for the residents, it would also save 15 months of construction time and either cost the same as or less than a surface route in this location.

The HSR system, known as HS2, is still under development, but plans call for a Y-shaped route that will connect eight of the United Kingdom’s 10 largest cities. (The country’s first HSR, called HS1, operates from St. Pancras in London and through the Channel Tunnel, connecting the United Kingdom to continental Europe). The first phase of HS2 will connect the capital of London with Birmingham via approximately 230 km of track and tunnels. Construction of this phase is anticipated to cost £16.3 billion in 2011 funds. Phase II—the arms of the Y— has an expected construction cost of £18.2 billion and will connect Birmingham to Manchester via a 153 km route to the west, and Birmingham to Leeds via a 187 km line to the east. It would also see the construction of a spur from London to Heathrow Airport.

The bored tunnel that is being proposed would extend an already planned 5 km twin bored tunnel to create a 14 km tunnel between Old Oak Common and West Ruislip, both in greater London. 

 The proposed Colne Valley Viaduct is located on the suburban fringe of London, along the new high-speed rail route to Birmingham

The proposed Colne Valley Viaduct is located on the suburban
fringe of London, along the new high-speed rail route to
Birmingham. Once the first phase of the project is complete, 14
trains will operate hourly in each direction. HS2 Ltd.

Initially the route was supposed to exit the 5 km tunnel and transition to an existing rail line along the Northolt corridor, according to Adam Joyce, a spokesman for HS2, who wrote in response to questions posed by Civil Engineering online. When that decision was made, “13 bridges along this section of the route had been identified as needing replacement,” Joyce said. “Replacement bridges along with the addition of appropriate mitigation measures (such as noise barriers) were seen as being the most appropriate route for the railway in this area rather than tunneling.”

At the request of community members, however, HS2 studied the merit of extending the 5 km tunnel. What they discovered, Joyce said, was that bringing the high-speed rail line to the surface along this section of the route would require that every bridge located along it be replaced. More extensive retaining walls and earthworks than previously anticipated would also need to be constructed along this section of the route, he said, and larger-than-expected tunnel portals would also need to be built: a 1 km structure at one end and a 650 m portal at the other. Additionally, both spans of a complex roundabout system known as the Hanger Lane gyratory would need to be replaced.

Extending the tunnel an additional 9 km under the area thus made more sense from a constructability standpoint. “We estimate the 14 km tunnel between Old Oak Common and West Ruislip would take 5 to 6 years to build—about 15 months quicker than if the Northolt to North Acton section was built on the surface,” Joyce said.

The proposed 9 km tunnel extension would require three vent shafts located between North Acton and Northolt.

The public comment period on the draft environmental statement and design refinements that began on May 16 gives community members and stakeholders an opportunity to respond to the proposal before the Secretary of State for Transport, Rt Hon Patrick McLoughlin MP, makes a final decision on the route and submits it to Parliament as a bill known as a “hybrid bill” later this year. If passed, the bill will grant permission for work to begin on the first phase of the revised plan to begin. Public comments on the draft environmental statement and proposed design refinements—which also include a revised proposal for the redevelopment of Euston station and a 2.6 km twin bored tunnel at Bromford, in the West Midlands—will be open until July 11, 2013.

The visual and noise impacts of the new lines on local communities are expected to be minimized by a combination of tunneling, cuttings, landscaping, and fencing, according to HS2. As currently designed, 70 percent of the surface tracks will be hidden from sightlines by fencing, landscaping, or cuttings. About 45 km of the first phase of the route—19 percent of the total—will be in bored tunnels, Joyce said.

HS2 will operate up to 14 trains per hour in each direction once the first phase is completed. Single units of the trains will be 200 m long, but they will be able to operate two at a time to seat 1,100 people.

The entire high-speed rail project is anticipated to generate benefits of £47 billion and fare revenues of up to £34 billion over 60 years, according to material contained on the HS2 website. The annual expenditure, spread over 20 years, is anticipated to be less than £2 billion, according to the organization.

The HS2 target date for royal assent (final approval) of the hybrid bill is 2015, with construction of the first phase expected to begin by 2016 or 2017 and to be completed by 2026.


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