HS2 wants to restart assembly of the pre-cast concrete 'green tunnel' in Northamptonshire in a week.
Construction was stopped in August after quality issues were recognized in "some segments". diggings and establishment work went on while tests were done on the segments.
A representative for HS2 Ltd told T&T: "Chipping Warden is the first of three green tunnels made of pre-Cast segments and it's essential that we spend the time to get the quality confirmation and construction process right. primary test results have been positive and we are effectively engaging with our supply chain partners to guarantee that we are prepared to restart assembly immediately. In the meantime, excavation and establishment works are advancing great and off-site segment manufacturing is progressing."
The representative wouldn't remark on the nature of the quality issues.
Development of the 2.5km tunnel at Chipping Warden in Northamptonshire started this summer and around 100m of the tunnel had been assembled when concerns were raised.
Planned as an M-formed double arch, the tunnel has separate parts for southward and northward trains. Rather than casting the entire tunnel on location, five different concrete pre-Cast segments are slotted together to accede the double arch - one central pier, two side walls, and two roof slabs. All the 5,020 segments are steel reinforced, with the largest weighing as much as 43 tons. The finished tunnel will be covered by earth and adapted to its surroundings.
The off-site producing process permits the tunnel to be constructed on the surface, with the purpose of accelerating construction, improving efficiency, and decreasing disturbance to the public.
HS2's major works contractor, EKFB, a consortium of Eiffage, Kier, Ferrovial Construction, and BAM Nuttall, developed the off-site approach, taking experiences from the development of the most recent French high-speed lines. It is the first it has been utilized in the UK.
Stanton Precast is making the segments for the whole three tunnels in a production line in Derbyshire.