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Crossrail’s Royal Oak Portal

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There are always developments going on beside the railway. Many go un-noticed. If you travel by train from South Wales into Paddington, there’s always been a mish-mash of sites just to the north of the main line.

The Westway A40 dominates the skyline and there have been rows of parked buses and lines of taxis in various states of assembly and colour. There’s even the Great Western Studios occupying a cold-war bunker style building.

But now, as you prepare to arrive at Paddington, being forever exhorted to “Make sure you have all your luggage and children with you” and to “Mind the blindingly obvious gap”, a glance over to the lineside reveals that everything has changed.

The buses have gone, as have the taxis and the seemingly immovable Great Western Studios have vanished.

Entrance to the underworld

All this is because of Crossrail – a major project that is well and truly under way.

On the invitation of Crossrail, the rail engineer has had a chance to view the completed approach to the Royal Oak Portal.

What might resemble a slip road in more rural surroundings is in fact the entrance to the underworld – the route for the project’s tunnelling machines and then, later on, the fleet of Crossrail trains.

Simon Pledger is Bechtel’s Project Manager for this part of the Crossrail scheme and leads us through the background engineering.

Narrow strips of land

A little bit of orientation may help. There are two sites involved. The Westbourne Park area will eventually accommodate the turn-back sidings for trains out of Paddington, along with a reinstated bus deck.

Originally the site of all the buildings and vehicles mentioned above, it also has a Tarmac stone terminal siding facility – which has to be moved.

The Royal Oak Portal site, which is just over half a mile from the bufferstops at Paddington, is just to the west of Westbourne Park. They are both narrow strips of land sandwiched between the A40 on its flyover and the London Underground and Network Rail tracks.

Buried services

The Crossrail parliamentary bill allowed for compulsory purchase orders for the land involved and, when all these processes had run their course, two contracts were let for demolition work.

Morgan Sindall undertook the clearance of the Westbourne Park area along with moving an existing retaining wall back to create a wider site for the ultimate relocation of the buses and for new sidings for Tarmac.

The Studios (Studio Space for the Creative Industries) have been relocated to just the other side of the A40.

Keltbray moved into the Royal Oak site to prepare the land for the portal works. In the process, ‘things’ were found. Simon remembers that, “We encountered at least 26 buried services across the site. It may have been more.

These and other obstructions to the movement of the Tunnel Boring Machines (TBMs) had to be removed. They included a thrust block to a cable chamber, a signal gantry leg and a selection of signalling location cabinets.

“We have implementation arrangements with Network Rail that allows them to do that work on our behalf.

“So far as plant working right by the London Underground and Network Rail tracks is concerned, there are a number of liaison mechanisms to ensure we adhere to undertakings and carefully protect their assets.

“We develop what we call ‘work package plans’ – effectively method statements for how we do the work. Where there’s an impact on their assets we share those method statements with London Underground and Network Rail over which they have approval rights.

“They’re also involved at the design stage and have what we call a final design submission that they get to approve – this basically tells them what we’re going to build.”

Excavating the approach to the portal. Photo: © Crossrail.

Temporary props

With the site cleared it was time to install the diaphragm walls. Most of these structures are of reinforced concrete placed in trenches filled with bentonite slurry. The bentonite keeps the trench sides stable and is displaced by the poured concrete.

The remaining part of the wall, completing a long box structure, was constructed using sheet piles. Temporary props were placed across the tops of the walls so that material could be excavated down to track formation level.

Some of these props were designed to remain in position as part of the permanent structure. Others remained in place only until the track base slab had been poured and had cured. At this point the props were removed.

The project was fortunate that the material arising was mostly from made ground. There were none of the issues of contaminated material so often encountered in urban and especially railway environments.

Leading the muck away

With the site being long and narrow, there were limited options for leading the muck away. The original contract had provision for carting material out via both the eastern and western ends. The eastern end sent haulage traffic out into Central Paddington.

The western end was land locked and was dependant on an agreement with the contractor occupying the Westbourne Park site.

An agreement was reached with Morgan Sindall that allowed CSJV (A joint venture between Costain and Skanska) to construct a haul road through the Westbourne Park site and out at the western end.

“It was a much better option because it allowed us to use both ends of the site and also it speeded up the programme with easier access and egress,” Simon Pledger recalled.

Traffic went out at set times throughout the day in accordance with the Section 61 agreement arranged with Westminster who were fully supportive of the spoil going out the West because of the reduced impact on Paddington Central area.

Most of the material – London Clay – went off to the Downes Barnes Golf Course in Hillingdon.

Lifting steel props by gantry crane. Photo: © Crossrail.

Ancient geological structure

All four sides of the new box structure have vertical extensions to cater for a ‘flood level 2’ – a fairly bland term for a major flood that would have the rest of London in trouble long before Crossrail!

On more mundane drainage matters, this large hole in the ground has temporary sumps and pumps to remove rainwater before the main cross-London tunnel drainage is installed.

The Natural History Museum had an interest in the excavations as they went through the Westbourne River. This ancient geological structure was found at about 11m depth and yielded around 160 (animal) bones, some of which appeared to have had ‘human intervention’.

This caused some delay. However the contractor did well to minimise any disruption by working with the archaeologists and eventually completed the job almost a month ahead of schedule. The subterranean riparian encounter had been expected because of earlier soils investigations.

Crossrail has a number of different sites which are likely to have significant historical interest and has a targeted ‘watching brief’ on these areas. An archaeologist will stand watching work in progress and as soon as they spot something they will ‘step in’.

The first phase portal structure is now complete – that is, the civils works for the purposes of allowing the TBMs to drive through London.

There is some additional scope of works to do once the tunnelling contractor has finished. Once the muck has been taken out from Bond Street and beyond and the TBM has emerged at Farringdon and been taken to pieces, the portal will be finished off and a headhouse erected.

Future programme

So, what next for Simon? “I’m looking at scoping the works that need to be done at Westbourne Park and Royal Oak Portal between the tunnelling contractor completing and the system-wide team coming through.

“So there is some scoping of works to get the buses back at Westbourne Park, an undertaking to manage the relocation of Tarmac and to put the sidings back.

“Still to do is the headhouse finishing for the portal, Network Rail’s Marcon Sewer drainage and the Green Lane Sewer drainage to accommodate the new Crossrail tracks.

“I’m setting that up at the moment and basically assisting the delivery team with some exercises trying to simplify our processes and to find additional value for money.”

A major item of Crossrail infrastructure has been completed.

The next things we will see (that is, if we pay attention as we arrive on our trains from the west) will be the TBMs being delivered in bits, being assembled and trundled down to the headwalls.

The rail engineer looks forward to an invitation to see it all close up!

Grahame Taylor
Grahame Taylorhttp://therailengineer.com

Structures, railway systems, railway construction, digital data

Grahame Taylor started his railway career as a sandwich course student with British Railways in October 1965, during which he had very wide experience of all aspects of railway civil engineering.

By privatisation, he was in charge of all structural and track maintenance for the Regional Railways’ business in the North West of England.

In 1996, he became an independent consultant, setting up his own company that specialised in the capturing of railway permanent way engineering knowledge using the then-new digital media. As a skilled computer programmer he has developed railway control systems and continues to exploit his detailed knowledge of all railway engineering and operations.

He started to write for Rail Engineer in 2006, and became editor two years later. During this time, he has written over 250 wide-ranging articles and editorials, all the while encouraging the magazine’s more readable style of engineering reporting.


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