Work on the UK’s longest railway bridge ramped up this week as HS2 began producing 1,000 enormous concrete segments.
The Colne Valley Viaduct will stretch for 2.1 miles (3.4km), carrying high-speed trains some 33ft (10m) above a series of lakes and waterways just outside north-west London
Deck segments weighing up to 140 tonnes are being made at a temporary factory nearby which was built specifically for the project.
The 328ft (100m) long building, which is visible from the M25 motorway, is larger than the Royal Albert Hall.
Each segment of concrete is a slightly different shape depending on where it will fit into the viaduct.
Around 12 segments will be produced each week at the peak of construction.
It's good to have a challenge
Engineers are using a technique known as match-casting, which involves pouring the concrete for each segment against the previous one to ensure they fit perfectly alongside each other.
The 1,000 segments will be supported by 56 piers resting on concrete piles inserted up to 180ft (55m) into the ground.
Designers of the viaduct were tasked with minimising its impact on the environment.
It will be set low into the landscape, taking inspiration from the flight of a stone skipping across water.
The segment factory’s manager, Ludovic Vergne, told the PA news agency: “It is not the size or the length of the bridge that is difficult.
“The challenge is the aesthetics that we need to provide. Each segment is unique.”
The Frenchman, who has more than 30 years’ experience of building bridge segments, went on: “Colne Valley is a very calm and quiet place.
“To put in place a typical bridge would not be very difficult, but they are trying to build something that has a better view.
“For me it is more difficult but it’s good to have a challenge.”
Production of the segments is expected to take just under three years, with the viaduct completed by summer 2025.
The work is part of a £1.6 billion contract handed to joint venture Align, which also involves building a 10-mile (16km) tunnel under the Chiltern Hills.
