“Quality issues” found in HS2 green tunnel segments

18 August 2022

Pre-cast segments forming HS2’s first ‘green tunnel’ are being tested after quality issues were identified in “a few segments”.

The Chipping Warden tunnel is the first of HS2’s three green tunnels made of pre-cast segments and an HS2 spokesperson said “it’s important that we take the time to get the quality assurance and installation process right”.

“We have recently identified quality issues with some of the segments and we are currently conducting tests to determine whether remedial work is needed. No decision has been made yet and we are actively engaging with our supply chain partners to resolve the problem,” the spokesperson said.

Excavation and foundation work is continuing on the site while the tests are conducted on the segments.

Construction of the 2.5km tunnel at Chipping Warden in Northamptonshire began earlier this summer and so far around 100m of the tunnel has been assembled.

Designed as an M-shaped double arch, the tunnel has separate halves for southbound and northbound trains. Instead of casting the whole tunnel on site, five different concrete pre-cast segments are slotted together to achieve the double arch – one central pier, two side walls and two roof slabs. All 5,020 segments are steel reinforced, with the largest weighing up to 43 tonnes. The completed tunnel will be covered by earth and landscaped to fit in with the surrounding countryside.

The off-site manufacturing process allows the tunnel to be built on the surface, with the aims of speeding up construction, improving efficiency and reducing disruption for communities.

HS2’s main works contractor, EKFB, a consortium of Eiffage, Kier, Ferrovial Construction and BAM Nuttall, developed the off-site approach, taking lessons from the construction of the latest French high-speed lines. It is the first time it has been used in the UK.

Stanton Precast is making the segments for all three tunnels in a factory in Derbyshire.

The spokesperson said “the lessons learnt at Chipping Warden in terms of quality assurance and the installation process will be applied when assembly begins on the other two tunnels”.

They added that all major structures on HS2 are designed to achieve a minimum of 120 years before major maintenance is required.