Tunnelling
Build
We will use eight custom-made tunnel boring machines to construct the tunnels. These giant machines will work nearly 24 hours a day excavating the ground and building the concrete tunnel walls as they dig. Two types of machines will be used to cater for the differing ground conditions along the route.
To control ground movement, the rate and the volume of excavated material must be kept equal with the machine’s advance. Pressure sensors continuously control this equilibrium. Advanced belt scales, a laser scanner and a density meter also assist measuring the volume of excavated material to pinpoint accuracy. These are continuously measured and monitored in realtime.
Design
We are building 42km of tunnels beneath London. Our experts have carried out extensive studies to carefully plan the railway’s path under the city. The tunnels will weave through the Capital’s congested sub-terrain, between underground lines, sewers, utilities and building foundations at depths of up to 40 metres.
The tunnel boring machine
Our tunnel boring machines work in pairs to build the 6.2m diameter tunnels needed for Crossrail trains.
148m Length of our tunnel boring machines - the equivalent of 14 London buses end to end
£10 million Cost of each tunnel boring machine
1,000 tonnes Rotating cutter head loosens the earth. Trimay/ Hardox plated and tungsten carbide tipped picks and disc cutters make the tools stiffer than steel and denser than titanium. Screw conveyor moves earth from the cutter head.
Rotating arm places segments with millimetre precision to form a ring. Hydraulic cylinders brace themselves on the newly positioned rings to push the machine forward at a force of up to 58,000kN. This is the equivalent to the force needed to lift over 2,900 London taxis.
Weight of each tunnel boring machine
100m Distance of tunnel built per week
6 million tonnes Excavated material from our tunnelling - enough to fill Wembley Stadium three times
Each ring is made up of eight segments and weighs 22 tonnes. Belt conveyor system removes earth from the machine.
Pre-cast concrete segments delivered to the segment feeder. Over 250,000 segments will be used to construct the tunnel walls. Segments differ in shape to enable the tunnel to curve. Conveyors move earth to the tunnel portal.
The tunnel drives We have developed an innovative programme using five tunnel drives. We are also rejuvenating the disused 19th Century Connaught Tunnel.
To Shenfield
To Maidenhead and Heathrow
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Tunnel Drives Royal Oak to Farringdon
Sub-surface station
Limmo to Farringdon
Surface station
Pudding Mill Lane to Stepney Green
Portal
Limmo to Victoria Dock
Tunnel
Plumstead to North Woolwich
Surface
Protecting buildings during tunnelling
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Shaft
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To Abbey Wood
We will use six earth pressure balance machines to drive through clay to the west of the River Thames and riverbed deposits to the east. The above diagram shows an earth pressure balance (EPB) machine. Two slurry machines will drive through chalk and flint beneath the River Thames. Slurry machines differ from EPB machines in three major ways: they have a
sealed, pressurised, air-locked chamber behind the cutter head; they have inlet pipes; and use an outlet pipe rather than a conveyor system to remove the earth. Bentonite, a mix of clay and water, is added to the cut ground in the chamber to form a liquid. The bentonite is separated from the excavated material at the tunnel portal and reused.
The construction of grout shafts will protect buildings during tunnelling and station excavation. The 17m deep shafts have small diameter pipes installed in an array from the base. The pipes extend up to 60m from the shaft.
When needed, engineers inject a cement-like substance (grout) at specific ports from the pipes deep into the ground to firm it. When they are no longer required the shafts will be backfilled and the ground reinstated.
Grout injection pipe Crossrail tunnels
Legacy
Working in partnership with the Skills Funding Agency, and with industry-wide sponsorship, we have developed the UK’s first training facility to provide people with the key skills required to work in tunnel excavation and underground construction. The academy will equip workers not only for jobs on Crossrail but also on future tunnelling projects in the UK and abroad. Through the academy and our commitment to providing apprenticeships, we are helping to revitalise the country’s construction and engineering skills base. We are also contributing to the development of new qualifications and health and safety standards across the tunnelling industry.
The material excavated from our tunnels will be beneficially reused. We will donate two-thirds of our excavated material to the Royal Society for the Protection of Birds to create a new 1,500 acre nature reserve at Wallasea Island in Essex. Wallasea Island will be one of the largest new wetland nature reserves in Europe. This reserve will help to compensate for habitat loss elsewhere in England and combat the threats from climate change and coastal flooding. Wallasea Island will provide a haven for wildlife including birds and seals. We will deliver the excavated material to Wallasea Island by rail and ship.
website www.crossrail.co.uk
e-mail
[email protected]
helpdesk 0345 602 3813 (24 hours, 7 days a week) Printed on recycled paper
