Two short but spectacular HS2 tunnels offer glimmer of hope for stalling project | Infrastructure

S.A few meters down, hidden deep beneath a hidden ventilation shaft in the Chilterns countryside, lies the buried treasure of HS2: two 10-mile tunnels built to avoid an eerily gorgeous area of ​​polished concrete of outstanding natural beauty.

A staff member working on the high-speed rail project laments what the entire route should look like by now: pristine, fully built and just waiting for a railway to pass through them.

The ballooning cost of HS2 and the construction delays that have hobbled the project have led to much soul-searching and fuss over the alleged national inability to build infrastructure.

From mothballed worksites in central London to abandoned routes in the Midlands and the north, many things have not gone to plan. However, this first look inside the completed 9 m diameter tunnels (the ventilation shafts are the last piece of the puzzle) shows what civil engineers with a clear mandate can do.

This was, ironically, one of the first areas of controversy when the rail route was redesigned. Uproar over the possible disruption (in the Conservative marginals no less) saw the decision to build the extended tunnel with HS2 nowhere near the law books.

Construction work there began at the start of the pandemic as politicians continued to consider the final route and scrapped Euston’s designs. The compound, which houses Align JV, a joint venture between Bouygues, McAlpine and VolkerFitzpatrick, which is HS2 Ltd’s main construction contractor for this section of the line, had a capacity of around 1,800 people at its peak.

The compound also served as the basis for the construction of the striking Colne Valley viaduct, a 3.5 kilometer railway bridge that spans nearby reservoirs. A concrete production facility was established on site for the viaduct and the subsequent 112,000 tunnel sections required. The two tunnel boring machines, brought from Germany, operated 24 hours a day, seven days a week, and worked in 12-hour shifts for 33 months from their first launch in 2021.

The main tunneling work was completed last year and the construction phase, along with the final wells, was officially completed. Mark Clapp, HS2 Ltd’s head of tunnel civil engineering, says those delivering a project of this scale and complexity on time “need to be confident that their hard work will stand the test of time”.

But building infrastructure is unpopular with locals, and Clapp is quick to sidestep mitigating measures, including rerouting business traffic as well as installing a sludge treatment plant on the site for millions of tonnes of excavated soil. “We removed the chalk from the soil and reused it to landscape the area to create a more chalky pasture; it is a rare and dwindling habitat and we added to it.”

Ventilation shafts, which must be large enough for emergency and maintenance access, were also designed with local impacts in mind. The headquarters near the village of Chalfont St Peter resemble small agricultural buildings at ground level; It masks a cave basement large enough to house huge fans and machines that can stand several stories above the ground.

According to HS2’s chief engineer, Mark Howard, the design also allowed the volume of the shafts to be minimised: “A lot of the talk was about the outage and what the main buildings looked like. The more you dig, the more you uncover – and twice the amount of spoil means twice the amount of trucks on the road.”

Tunnel portals feature more innovation: a funnel-shaped opening designed to stop the sonic boom that high-speed trains can produce when entering at 200 miles per hour. Japanese bullet trains have a 18-metre-tall tapered nose to prevent bursting when exiting tunnels, but for physical and economic reasons the UK has been unable to do the same: “This protruding piece would hit the old Network Rail infrastructure. And it takes up around 40 seats,” says Howard.

Laboratory tests to understand micro-pressure waves involved shooting miniature trains on elastic bands through tubes, resulting in the construction of 200m-long perforated concrete funnels to stop the boom.

Eventually, trains will emerge from these crossings in just three minutes about 10 miles north of here. But it may take another decade for this three-minute journey to begin. Next comes the installation of mechanical, electrical and plumbing equipment. This will be followed by rail systems, including rail to the powertrain and electrical equipment on the roof. Years of testing would follow.

And first, the entire HS2 structure is expected to be reset. Progress on the Chiltern tunnels makes them outliers, even in tunnels from London to Birmingham that were once only stage 1. The original £32.7 billion budget, which includes the Leeds and Manchester lines, is expected to be revised to over £80 billion at current prices.

A spokesman for HS2 Ltd said: “Our managing director, Mark Wild, has made clear that the overall delivery of HS2 is unacceptable and is committed to ending the project’s cycle of cost overruns and delays.

“Over the last year he has led a comprehensive review examining every part of HS2, creating a framework to build the railway efficiently and at the lowest reasonable cost. This means getting the construction program back in the right order, transforming HS2 Ltd into a leaner delivery company, restarting our relationship with the supply chain and delivering significant improvements in productivity.”

Although more than a year has passed since Wild took over as CEO in December 2024, the promised reset itself appears overdue. But following wholesale changes made by previous governments that resulted in phase 2 being canceled overnight in Manchester, ministers have vowed to give Wild time to draw up what they hope will be a decisive plan.

Wild’s initial assessment, sent to the transport secretary last March, was that hopes that HS2 would be up and running by 2033 were unattainable. Since then, Wild and the Ministry of Transport have been working on what could be done, when and at what cost.

The leadership team has been revamped, including the recruitment of former London Transport commissioner Mike Brown as chairman. But hundreds of other corporate roles were canceled in favor of front-line civilian distribution jobs. Meanwhile, commercial renegotiations with the supply chain continue this year to create contracts that do not pass balloon costs back to taxpayers.

Last week ministers said there was still “an intention” for a line from Birmingham to Manchester connecting to Northern Powerhouse Rail; even though they emphasize that this will definitely not be another part of HS2.

Wild, whose last job was to lead Crossrail to open the Elizabeth line to a restructured budget and schedule, may face a tougher task in restoring the progress and reputation of Britain’s high-speed rail. However, when it is opened, there may still be many things to be amazed by.