Increasing capacity on the East Coast Main Line with a pioneering new tunnel
As part of our £1.2billion East Coast Upgrade, we’ve increased capacity for passenger trains on the East Coast Main Line by building a new two-track railway line that dives under it at Werrington, north of Peterborough.
The fly through video below visualises how the new dive under works when in operation.
The new line removes constraints to the timetable caused by slower freight trains on the Great North Great Eastern (GNGE) route having to cross over the high-speed East Coast Main Line.
The new dive under provides an alternative route by enabling the new two track railway to run underneath the East Coast Main Line instead, separating it from any high speed passenger traffic.
The north ramp was constructed by installing 183 x 18 metre-long, 900mm diameter, rotary bored contiguous piles and over 900 x eight to 10 metre-long soil nails, finished with sprayed concrete facing. In total 120,000m3 of soil and clay was excavated to create one of two 940 metre ramps.
Final fit out of the north ramp commenced following the ‘curved box’ structure being pushed in to position in January 2021.
In February 2020, our tunnel boring machine, named ‘Chloe and Georgia Whiteman’ after the daughters of Mark Whiteman, a colleague, who tragically passed away unexpectedly in 2019, was launched into the ground to begin the work of boring two three and a half metre diameter, 168 metre-long guide tunnels underneath the operational railway.
Thanks to the state of art remote track monitoring equipment which constantly measured the position of tracks, tunnelling was successfully completed, unnoticed by the trains passing above, at the start of August 2020.
The tunnels were fitted out with the required slide and guide plates inside to support the pushing of the ‘curved box’ into position under the East Coast Main Line.
South Ramp and South Dive Under Entrance
Mirroring the north ramp, a second 940 metre ramp was constructed to the south of the dive-under, in the enlarged area made by the slewing of the Stamford Lines.
The Reception Pit, which was used to receive and recover the tunnel boring machine from the ground, was completed in April 2020. Works included the installation of 66 x 18-meter-long bored contiguous piles and the excavation of over 2,000m3 of soil and clay.
Piling for the South Ramp was completed in August 2020 and allowed excavation of the ramps to commence.
The South Ramp consists of 693no. 900mm diameter, bored contiguous piles up to 18m in length, and a further 340 metres of 10 metre sheet piles.
Relocating the Stamford Lines at an earlier stage enabled the South Ramp to be constructed with no impact to the operational railway or passengers.
From March 2020 work began to build the dive-under structure.
The ‘curved box’ was built next to the East Coast Main Line in nine, interconnected sections. The structure was 155m long, 9.5m wide and 5.1m high, with 1m thick walls and soffit.
It weighed just over 11,000 tonnes, which is 1,000 tonnes heavier than the Eiffel Tower!
The ‘curved box’ was pushed under the East Coast Main Line using large jacks to propel and steer it during January 2021.
A trial push took place in December 2020, when the box was pushed forwarded by 16 metres to allow the structure to be weighed, the centre of gravity to be identified and all equipment to be calibrated and checked.
Over Christmas 2020, a bespoke signalling solution was installed and tested on the two ‘Stamford’ tracks running alongside the construction site. This work enabled a partial train service to continue to run on the East Coast Main Line while the tunnel was being pushed into place in January 2021.
The big push
During a nine-day partial closure of the East Coast Main Line in January 2021, the 11,000 tonne, 155-metre curved concrete box tunnel was pushed into place.
Time-lapse footage below shows the 11,000 tonne curved concrete box being pushed under the East Coast Main Line.
Whilst hydraulic jacks at the rear pushed the tunnel portal forwards at just 150cm per hour, excavators at the front broke away the guide tunnels to reveal the glide plates to guide and steer the tunnel into position.
This was the first time that a curved concrete box has been installed using this industry-leading engineering technique in the UK.
Teams removed three of the tracks, lifted the overhead wires and dug out spoil from the site. Once the tunnel was eventually underneath, they then put everything back in place ready for regular services to resume.
In September, Network Rail completed major signalling work ready for freight trains to use the dive under, with engineers commissioning the signalling system over a weekend, marking a major milestone in the final stage of the project.
Vital work to test the new tunnel then took place will take place, with trains starting to use the new infrastructure in December 2021.