Crossrail will use eight tunnel boring machines (TBMs) to construct the new tunnels under London. The giant machines will carefully weave through the capital's congested sub-terrain, snaking between the existing Tube network, sewers, utilities, and London’s hidden rivers at depths of up to 40 metres.
The custom made 1,000 tonne and 150 metre long machines are giant underground factories that are not just tunnelling, but removing the muck and creating a sealed concrete tunnel as they go.
Each machine has a rotating cutter head at the front, and a series of trailers behind, housing all the mechanical and electrical equipment required for the excavation of material.
Each TBM weighs approximately 1000 tonnes and will be up to 140m in length with an external diameter of 7.1m. This allows for an inside tunnel diameter of 6.2m once the concrete tunnel segments are in place.To construct the 42km of tunnel required for Crossrail the tunnel boring machines will undertake ten individual tunnel drives to construct the 6.2m diameter rail tunnels.
The push force of these powerful machines is huge- equivalent to the force needed to lift over 2,900 London taxis.
At the front of the TBM is a full face cutter head which rotates at around 1 to 3 rpm. As the TBM advances forward the cutter head excavates the ground. The loosened material is removed from the cutter head via a screw conveyor, which moves the material through the back of the TBM and out of the tunnel via a conveyor belt.
Close to 100% of the excavated material will be reused. Three quarters is being delivered by rail and ship to Wallasea Island in Essex to create a new nature reserve in partnership with the RSPB. All excavated material from the western tunnels will be transferred by freight train from Royal Oak Portal to Northfleet.
There will be two different types of TBM to reflect the differing ground conditions along the Crossrail route. Six will be Earth Pressure Balance Machines, which will be used for the main running tunnels between Royal Oak and Pudding Mill Lane.
These will pass through ground which is predominantly London clay, sand and gravels. The Thames Tunnel, which is predominantly constructed through chalk, will use Slurry TBMs.
Our first pair of TBMs, Phyllis and Ada, were delivered to Westbourne Park just west of Paddington, in early 2012 where they were assembled and tested ahead of launch in May and August respectively. Elizabeth and Victoria, Crossrail's second pair of TBMs, were delivered to Limmo Peninsula in London’s Docklands in summer 2012.
Two further TBMs, Mary and Sophia, are undergoing factory testing and will be delivered to Plumstead Portal later this year. They are Crossrail's only mixed-shield, or "slurry", TBMs and will be used to construct the Thames Tunnel.
A fourth pair of TBMs, yet to be named, will be used to construct the tunnels between Pudding Mill Lane and Stepney Green. The eight TBMs will undertake a total of ten individual tunnel drives to construct the new 6.2m diameter Crossrail tunnels.
The eight tunnel boring machines will be used as follows:
- Royal Oak to Farringdon (Drive X) – 2 x earth pressure balanced TBMs
- Limmo to Farringdon (Drive Y) – 2 x earth pressure balanced TBMs
- Pudding Mill Lane to Stepney Green (Drive Z) – 2 x earth pressure balanced TBMs
- Limmo to Victoria Dock Portal (Drive G) – 2 x earth pressure balanced TBMs re-used from the Pudding Mill Lane to Stepney Green drive
- Plumstead to North Woolwich (Drive H) – 2 x slurry TBM
To help reduce the likelihood of settlement while the tunnels are constructed, the TBMs have to run nearly 24 hours a day, 7 days a week, 365 days a year. There will be scheduled breaks to allow maintenance on the TBMs to take place.
Each TBM will be operated by a ‘tunnel gang’ comprising of around twenty people - twelve people on the TBM itself and eight people working from the rear of the machine to above ground.
Gallery - Crossrail's giant tunnelling machines
Naming our tunnelling machines
According to tunnelling tradition, a TBM cannot start work until it is given a name. This tradition is carried out throughout the world as a sign of good luck for the project ahead. Since our TBMs will operate in pairs to deliver the east and westbound tunnels for each of the tunnel drives we decided to name them in pairs.
Throughout January 2012 we ran a competition inviting the public to suggest pairs of names for the first 6 TBMs that will be used to construct the new tunnels. We received a fantastic response from across the UK with over 2,500 entries submitted.
A Crossrail panel drew up a shortlist of 10 pairs of names and these were published on our website, with the public invited to vote for their favourite pair of names throughout February.
Around 4,500 people voted and the three pairs of names that received the most votes were:
- Ada and Phyllis (submitted by Emma Duncan, London):
Ada Lovelace was one of the earliest computer scientists. She worked with Charles Babbage on his ‘analytical engine’, and is regarded as having written the first computer program. Phyllis Pearsall single-handedly created the London A-Z. A portrait painter, she got lost on the way to a party in 1935 and decided the maps were inadequate. She walked 23,000 streets, and a total of 3,000 miles to compile the map, delivering the first 250 copies in a wheelbarrow.
- Victoria and Elizabeth (submitted by Bryan Evans, Burnham):
Named after the two Queens, Victoria was monarch in the first age of great railway engineering projects and Elizabeth is the monarch at the advent of this great age of railway engineering projects.
- Mary and Sophia (submitted by Ray King, London):
Mary was the wife of the famous railway engineer Isambard Kingdom Brunel and Sophia was the wife of Marc Isambard Brunel who built the first tunnel under the Thames.
As these giant machines go to work constructing the new tunnels beneath the busy streets of London you can track their progress on our Near you mapping tool.
Tunnel construction schedule:
|Tunnel drive||TBM launch||Tunnel drive complete|
|Royal Oak to Farringdon (Drive X)
||Third Quarter 2013|
|Limmo Peninsula to Farringdon (Drive Y)
||November 2012||Third Quarter 2014|
|Pudding Mill Lane to Stepney Green (Drive Z)||Fourth Quarter 2013||Third Quarter 2014|
|Limmo Peninsula to Victoria Dock Portal (Drive G)||Third Quarter 2014||Fourth Quarter 2014|
|Plumstead to North Woolwich (Drive H)||First Quarter 2013||Second Quarter 2014|