The tunnelling is finished. It’s time to start building a railway. Ok, here at Rail Engineer we’ve taken an interest in the Crossrail tunnelling machinery. We’ve marvelled at the wonders of steering a delicate path through all the services and foundations beneath London. We’ve looked at the logistics of shifting all the spoil and the creation of a wetland nature reserve twice the size of the City of London at Wallasea Island in Essex.
But we’re really railway engineers, not tunnellers, and so it’s now, with the tunnels completed, that our enthusiasm for the project really kicks in. Over the coming months we’ll be looking at how an almost bare tunnel will be kitted out with the paraphernalia of a railway and how all that stuff is integrated to form a complete system capable of running a service of up to a train every two minutes.
This month, David Bickell covers the signalling and the transition from Network Rail to the Crossrail system and back again. In future issues, we’ll be looking in detail at the track installation equipment and how everything fits together, as well as delving into the power requirements and the overhead power delivery system.
And amongst all this there will be coverage of the logistics involved in not only feeding this voracious project but how all the various sites are kept safely apart. Of course, everything will depend on telecoms right through and beyond the construction phase.
But this is all to come. In the meantime we look at how things are at the moment with the rumble of the tunnelling machines now a thing of the past.
The contractor undertaking the Crossrail railway systems main works, contract C610, is ATC – a Joint Venture comprising Alstom, Transports Sud Ouest (TSO) and Costain Limited.
Gregg Purcell (Crossrail’s railway systems construction manager) and his team weren’t waiting for the last bucket of spoil to be transported along the Thames before they got into the tunnels. As each TBM receded into the distance, and its roar became more and more muffled, the railway began to take shape behind them.
The bore has not been left as a plain tube. It’s not entirely without a railway form. The tunnel construction team built mass concrete – ‘first stage’ concrete – up to just below slab track level along with walkways on either side. These walkways are a crucial part of the scheme of things.
It is on them that specialist multi purpose gantries run conveying the first components to make up the track structure, as we’ll see in a moment.
The track support comes in five different assembly types:
» There’s direct fixed track – used in the Victorian-engineered Connaught Tunnel;
» For most of the railway there’s standard track slab using fibre reinforced concrete;
» High attenuation sleepered track – similar to standard slab – is used only in a few small areas to reduce noise/vibration;
» Floating track slab (light) is used to reduce noise and vibration underneath Soho;
» Floating track slab (heavy) will be installed to reduce noise and vibration underneath the Barbican.
Direct fixed track has been used within Connaught Tunnel. The track bed, a concrete reinforced structure, allows engineers to create a flat surface on top of the significant undulations in the ground and to work within the height restrictions which are a feature of this Victorian- engineered tunnel. A total of 2.6km of direct fixed track has already been installed.
Floating track slab (light) goes in between Tottenham Court Road and Bond Street to minimise noise and vibration impacts from the operating railway on nearby recording studios and hotels which is a requirement of the Crossrail Act. The track slab is cast and then jacked up so that it ‘floats’ on a combination of elastomet rubber bearings and heavy-duty springs installed beneath it. A total of 1.97km of floating track slab (light) will be installed.
Floating track slab (heavy) will be used in the Farringdon area due to the close proximity of the Barbican. It sits on heavy-duty springs. A total of 1.34 km of floating track slab (heavy) will be installed.
Due to the extra depth added by the spring base of the floating track, a stiff shallow slab is needed. To ensure that the shallower slab remains durable and effectively minimises noise and vibration, an unusually dense concrete called Magnadense is used. Magnadense, manufactured by LKAB Minerals, is over twice as dense as normal concrete due to its natural iron ore content.
Behind this one word, Magnadense, lies a whole story of engineering discovery in the UK. It’s a concrete type used extensively in Sweden as a way of making sure that house basements are heavy enough not to float in the high water table over there. There has been little use in the UK until now and so this has been a steep learning curve.
Gregg’s aside: “On the team is a gentleman who has poured vast quantities of the stuff in the French nuclear industry and his experience has helped with a range of novel issues that we have had to overcome.
This concrete is so dense that a full concrete lorry will be heavily overloaded. Road vehicles have to run half full to keep within standard HA loading. Batching plants have to learn how to handle it. Costs rise.”
Short test tracks will be used to test the construction methods, materials and equipment as well as for training purposes. A 100 metre long stretch of standard track slab has been built at Plumstead, a 30 metre section of direct fixed track has been constructed beside the Connaught Tunnel in Silvertown, and a 100 metre curved section of floating track slab has been built at Old Oak Common.
The majority of the track in the central section (about 80%) is standard track slab. This amounts to a total of 41.2km.
When constructing the standard track slab, the initial sequence of work is carried out by four multi- purpose gantries which transport and accurately position around 70,000 sleepers and 57km of rail in Crossrail’s central section. Each gantry, operated by a single person, will run along the raised curbed sides of the tunnel’s first stage concrete mentioned earlier.
After positioning 108-metre- long sections of rail along a stretch of tunnel, the gantry then carries and deposits sleepers at carefully measured intervals before lifting the rail into place on top of them. The track is then secured in place using clips, props and jigs before it is welded and the formation is concreted into position.
Two gantries will operate from Plumstead, one from Westbourne Park and the other will install the floating track slab underneath the Barbican estate.
The bespoke gantries have been manufactured for Crossrail by Metalliance in France and were delivered to London in August 2015.
The two main temporary logistics centres for Crossrail’s railway systems are located at Plumstead in southeast London and Westbourne Park in west London. These will be used by the many different engineering trains during the fit-out of the tunnels and stations.
Plumstead is the larger of the two railheads with a total of eight tracks, an overhead gantry crane to supply engineering trains and an operations centre to coordinate the activity.
At Westbourne Park, the previous railhead that was constructed for the transport of excavated material from the western tunnels is being replaced with a new three-track railhead. The materials needed for the western tunnels fit-out will be stored and loaded onto construction trains at a temporary storage depot at Old Oak Common and brought to the Westbourne Park railhead.
The concreting train is a sophisticated mobile underground concrete batching factory, which is the reason for its significant length. Dry materials are loaded onto the concreting train, which then batches the concrete. At 465 metres long, this train plays a key role in creating the standard track slab. Refurbished and brought to the UK from France via the Channel Tunnel in August 2015, it will be based at Plumstead and used in the installation of standard track slab. At its peak production rate it will be able to install up to 250 metres of concrete track slab a day.
Running and maintaining the concreting train is a 24-hour operation. Concrete pouring will take place during the night with restocking and maintenance being carried out during the day. When the concreting train is not operating in the tunnels, it will be split in two due to its size and will be located on two of the eight railhead tracks.
A concreting shuttle will be used to construct the standard track slab in the tunnels between Royal Oak Portal in west London and central London. Pre-mixed fibre reinforced concrete, provided by a batching plant at Paddington New Yard, will be loaded onto the shuttle. The concrete shuttle will be delivered to Westbourne Park in January 2016.
The main difference between the train and the shuttle is that the train is loaded with dry materials, the shuttle with conventional ready-mixed concrete. It has around half the output of the concreting train but is much shorter – a factor driven by the limited room available at its stabling point in Westbourne Park.
Gregg observes that, with the shuttle, “you’re up against the clock the moment you load it up!”
Around 70,000 sleepers have been manufactured for Crossrail by SBC Rail (Stanton Bonna) in Nottingham, a Consolis Holdings (SAS) company. These sleepers will be delivered into the Crossrail tunnels in bales by construction trains from Plumstead and Westbourne Park.
A specialised welding machine will be used to join the 108-metre-long sections of Crossrail’s permanent rail together. Tata Steel will supply more than 57km of its heat-treated, wear-resistant rail. The steel blooms are being manufactured at Tata Steel’s plant in Scunthorpe before being rolled at the company’s Hayange
mill in northern France and delivered to the Plumstead Railhead via the North Kent Line. Tata Steel will also deliver rail to the Westbourne Park railhead from January 2016 to support the track installation process in the western tunnels.
As part of the tunnel fit-out, over 250,000 holes will be drilled to accommodate brackets for cabling, walkways and other equipment to support the operation of the railway.
ATC Joint Venture will deploy a state of the art, precision automated drilling rig which will drill many of the holes required, minimising the need for manual drilling. The Crossrail drilling rig was manufactured by Rowa Tunnelling Logistics in Switzerland and arrived in November 2015.
Once the track slab has been laid, the rig will sit on the track and move its way through the tunnels drilling the holes in pre-determined locations. The machine has a dust suppression system in place, producing a clean and accurate drilled hole every time. The drilling rig works in conjunction with real-time 3D laser surveys of the tunnel to ensure accuracy.
The Crossrail route will be powered by a 25kV overhead line system. A rigid overhead conductor bar will be installed in the tunnels.
In the central section, traction power for the Crossrail trains will be provided by two new bulk supply points from National Grid at Pudding Mill Lane in the east and Kensal Green to the west.
A 22kV high-voltage network will be installed by AC (just Alstom and Costain without TSO) in the central section from Royal Oak Portal in the west to Limmo Peninsula in the east with an 11kV high voltage non-traction spur to be installed from Limmo through to Plumstead. This network will supply mains power to each Crossrail station, shaft and portal within the central section.
Crossrail’s communications and control systems
New communications and control systems will be installed throughout the new Crossrail stations and tunnels. These include:
» Customer information systems – customer information displays in ticket halls and concourses and at each platform screen door;
» CCTV – Digital cameras for station control and security while views of the platform are also transmitted to the drivers cab for driver only operation (DOO);
» Radio – Provision of radio infrastructure / network for operations and emergency services;
» Public Address System – For general and emergency announcements.
Current Crossrail progress
Construction of the logistics centre at Plumstead is complete. The construction of the Westbourne Park temporary railhead is underway.
The first delivery of permanent rail was made in August 2015 and installation of permanent track is also underway.
So, that’s the state of railway engineering on Crossrail. If you’re really bereft of the delights of tunnelling, then there will be three whacking great machines chomping their way through the London Clay from next year. However, these will be constructing the Thames Tideway – a tunnel just a little larger than Crossrail, but which will be transporting something considerably less wholesome.