Over Christmas, part of the East Coast main line moved 20 metres westwards as enabling works for the £200 million Werrington Grade Separation project to construct an underpass at Werrington Junction near Peterborough.
The existing Werrington junction layout causes constraints on increasing the frequency of passenger services, as slow freight trains moving onto the Great Northern Great Eastern route (GNGE) need to cross over the three high speed lines of the East Coast main line.
Network Rail and its designer, Jacobs, considered a number of options for grade separation, comprising both under and overline options. Local public consultation in summer 2014 presented these and 400 people attended events, with a strong majority favouring the underpass solution.
Public feedback received was collated and analysed and used to help inform Network Rail’s selection of the preferred option. Key concerns raised were the potential environmental and community impacts, especially noise, given the proximity of the railway to properties. An overline option would require a very high viaduct that would have to also cross the higher level A15 trunk road and, for many, the visual intrusion of this on the very flat landscape was a key concern.
The underpass option was selected, recognising public concerns but also reflecting the technical, environmental, cost, maintenance and constructability issues and constraints.
In Autumn 2016 the single preferred option was presented in four local public consultation events, enabling concerned residents to review the plans for the scheme, speak to members of the project team and provide their feedback. This enabled Network Rail to address any remaining queries before the detailed design of the underpass option was finalised.
Network Rail submitted a Transport & Works Act Order in 2016 to begin work on the project and this was approved in 2018.
The plan
The Werrington grade separated junction project involves the construction of a rail chord to provide a new connection between the ECML and the GNGE line. This will be a massive 3km-long undertaking.
From south of Cock Lane footbridge, a central pair of tracks for the GNGE chord will take a ramp into a new underpass, below the ECML, and rise to meet the GNGE line approximately 600 metres after Lincoln Road. The new chord will use the footprint of the existing Stamford lines, which will be realigned, the Down line moving up to 20 metres westwards and the Up moving 10 metres east onto the existing wideway between the ECML and Stamford routes.
The new underpass itself will be a 155-metre-long curved structure jacked under the ECML. A maintenance access bridge beneath the Stamford lines will give access to its southern portal.
East of the ECML, the new chord will pass under the A15 using the alignment of the existing Hurn Road, which will be diverted, and beneath a new bridge under Lincoln Road.
The project began on site in March 2019 and is due for completion in March 2021. It forms part of the wider Network Rail East Coast Upgrade, which also includes works at London King’s Cross, Stevenage and a number of other smaller projects that collectively will allow an additional two high-speed paths per hour between London and Doncaster.
The project is being managed on the hub and spoke model. Network Rail is providing management, Morgan Sindall, the principal contractor, is constructing civil works and OLE structures, signalling is being installed by Siemens and the permanent way works by the Central Rail Systems Alliance (made up of Network Rail, Balfour Beatty, Atkins and TSO).
The scale and scope of this project includes a very wide range of activities and the design team reflects this. Jacobs was appointed by Network Rail as the lead design organisation to deliver the GRIP 3 option selection design. Signalling design and telecoms data transmission design were delivered by the Network Rail Signalling Design Group. Once appointed, Morgan Sindall provided early-contractor-engagement support to ensure that constructability was fully considered in the design.
The delivery of GRIP 4 and GRIP 5 detailed design was carried out by Morgan Sindall supported by lead designer Mott MacDonald and by Tony Gee & Partners.
Siemens delivered the detailed signalling and telecoms design. GSM-R design is by Network Rail Telecoms and track bed design by the Network Rail Track Bed Design Team in Birmingham.
Difficult designs
The scheme has included a number of geotechnically challenging aspects, such as de-watering of artesian pore pressures in the various underlying strata and dealing with Oxford Clay, with its residual shear planes.
Working together, the two designers – Mott MacDonald and Tony Gee – had to deliver both heavy civils and temporary works packages. These included over 450 metres of propped contiguous piled wall, 150 metres of soil nailed cutting, a steel/concrete composite integral bridge, 55 metres wide and with a 15-metre span, a 150-metre-long curved jacked portal and its associated temporary works, including TBM (tunnel boring machine) launch and reception pits, jacking slab and cutting shield.
Works during 2019
Works began in the Spring with the setting up of the site compounds. The main compound is on the west side, accessed through an industrial estate, and is the base for the track realignment, south ramp and retaining structures. A smaller one on the east side, accessed from the A15, is responsible for the jacked box construction and connection works to the GNGE route.
This project is alongside the western edge of Peterborough, close to many properties and audible to many more, and so engagement with neighbours is very important. The dedicated communications group for the ECML project was responsible for engaging with the community, highlighting to them the benefits of the scheme and warning of potential noise and disruption, especially during the occasional night works. The relationship with neighbours has been extremely good so far, despite the noise of piling and excavation which spreads far in this flat terrain.
One of the early preparatory tasks before the major works began was the diversion of a number of significant Anglian Water, UK Power Networks and Vodafone utility assets.
A stream, Brook Drain, which ran alongside the boundary, has been moved westwards to make way for the new formation. Sized to help with local flood issues, the new river is 840 metres long and four metres deep. It features a meandering channel, including riffles – shallow sections of water – and side pools, where aquatic wildlife can take refuge. During environmental surveys, the rare Four-spotted moth was found living on the riverbank. A habitat for these was designed into the new channel. At the southern end of the project, 0.5km of the stream has been diverted beneath the realigned Stamford lines, within a concrete box culvert.
At the south end of the project, Cock Lane Footbridge was replaced with a new longer structure, maintaining access from Benedict Square to Stirling Way and spanning the realigned Stamford and GNGE lines. This new 50-metre-span structure was designed by Mott MacDonald, fabricated by Britton Fabricators and erected during October and November. The footbridge is a steel structure throughout with exception of the upside pier, which is close to the Up Slow and is a heavy reinforced concrete structure, designed to resist derailment impact loading.
Following the completion of the footbridge and Brook Drain works the formation for the diverted Up and Down Stamford lines was constructed. Clay excavated from the site was used to backfill the old Brook Drain. The new formation is built on natural ground overlain with a geotextile and 200mm deep sand-filled geocells ensuring a minimum 45MPa bearing pressure.
G44 concrete sleepers and CEN60 rail were delivered by road and the 3,580 metres of plain line was installed on 250mm bottom ballast, welded and tamped in advance of the Christmas and New year tie-ins.
New overhead line equipment included new piled foundations, structures, and wiring to the new Down Stamford line.
New signals, four-foot equipment and lineside location cases were installed along the new alignment and tested prior to commissioning over the tie-in possessions. Within Peterborough signalling control panel, works were carried out, to alter the panel to accommodate the commissioning of the new alignment and enabling works to allow pre-testing of the system leading up to the complete project commissioning works at the end of 2020.
At the North end of the realigned section, a top-down constructed bridge has been installed. This will provide the access for construction traffic and for future maintenance within the underpass.
To the north of the ECML, much of the north ramp has been constructed and preparatory earthworks have begun forming the new formation for the chord line. In total, over 120,000 cubic metres of soil and clay have been excavated to date.
The first section of the north ramp consists of contiguous piled walls with steel overhead bracing. 183 rotary-bored piles, each 900mm diameter and driven 18 metres deep, were installed by Bauer Technologies using a BG45 PremiumLine Rotary Drilling Rig. This section forms the jacking slab for the two 168-metre-long, three metre diameter bored tunnels that will house the box jacking guide rails and for jacking the box itself. The 750mm thick temporary jacking slab incorporates slide track and jack reaction pockets and is supported on 30 1.2-metre-diameter bored piles.
Beyond this section the formation passes through a steep cutting supported by 900 soil nails, installed by BAM, each eight to 10 metres long, and by a sprayed concrete facing.
At the A15 bridge Hurn Road passed through one of the two spans, the existing GNGE through the other. The road has been diverted, so that the new chord can be laid through its span, a rare example of a road being changed to a railway. A new bridge is being constructed beneath Lincoln Road and a 41-metres-long temporary footbridge has been provided for pedestrians. To accommodate these works, a pair of semi-detached houses were purchased and demolished. One bungalow was also demolished as part of the Hurn Road diversion.
North of the end of the project, as part of the project enabling works, two ponds were constructed near Fox Covert footbridge to re-house Great Crested Newts.
Works during Christmas
The Christmas period saw the realignment of the Stamford lines by up to 20 metres to the west, so creating a central wideway for the following construction of the south ramp. As the plain line had been completed in advance, only the tie-ins at each end remained to be completed over two 53-hour disruptive possessions – on 24 to 27 December for the Down Stamford and 4 to 5 January for the Up.
The signalling works carried out over the Christmas period were relatively minor with the real risk being timescales to complete the lineside build of the signalling system, following construction of OLE and track assets.
The existing track was lifted out by road/rail excavators and new plain line panels and ballast unloaded from an engineering train on the opposite track.
The redundant track panels were lifted out in 60’ panels, stacked by the excavators and removed from the site using a pair of tracked McCulloch Rail Lifters into the compound where they will be removed by road to Whitemoor Rail Recycling Centre to be reused as serviceable material.
After each of the two possessions, works were completed on time and handed back with a planned 50 TSR (line speed 80). During these possessions, some train services were diverted, and a bus replacement service was provided between Peterborough and Leicester.
Future works during 2020
With the Stamford lines repositioned, the construction of the south ramp can begin, with traffic entering the site through the maintenance access bridge. This work is due for completion in June. Once complete, the Up Stamford will again be moved, this time to its final location, to the east of the ramp. The retaining structures for the ramp will be 693 contiguous bored piles, 900mm diameter, up to 18 metres in length, the shallow sections at the ramp top will be of AZ26-700 steel sheet piles up to 10 metres long.
During the summer, Morgan Sindall will construct the concrete box – the jacked portal – that will later be pushed into position to form the underpass beneath the ECML. This is a cast concrete structure, 155 metres long, curved at 750 metre radius on plan, 9.5 metres wide and 5.1 metres high. The walls and roof are one metre thick and the whole box weighs 11,000 tonnes.
Designed by Mott MacDonald and Tony Gee, it includes fitment for a hydraulically linked lateral guidance system to move the portal around the plan curvature and to resist out-of-balance horizontal soil pressures during the push. This is the first time that a curved portal has been jacked in this configuration in the UK.
A 200-metre jacking slab was constructed in a deep cutting between contiguous piled walls. Because of the ground conditions, designers had to determine the effects of soil slumping against the sides of the jacked portal during the push.
Once the jacked portal structure has been constructed off-line, installation will take place during a nine-day blockade of the ECML in the first two weeks of September. After removal of permanent way, earthworks and OLE equipment, it will be pushed (jacked) into place using a 5,000-tonne jacking force, the box running along slide tracks, pre-installed within 3.21-metre-diameter pre-bored tunnels.
Once the box is in place, the track can be restored to its planned layout and the whole project should be complete in 2021.
Rail Engineer will be back to report on the ‘Big Push’ in September.
