Your Guide to Ground Treatment

• Why ground treatment is necessary

• What grout shafts are

• How grout shafts will be used on the construction of Crossrail

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Crossrail

Information about Crossrail is available in a range of languages, audio, Easy Read and Braille.

Please tick the relevant box to show the format you require. Include your name and address and return to Crossrail at the address below.Name: Address:

CrossrailInformation about Crossrail is available in a range of languages, audio, Easy Read and Braille. Please tick the relevant box to show the format you require. Include your name and address and return to Crossrail at the address below.

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Please return to: FREEPOST CROSSRAIL No stamp or address required E-mail: helpdesk@crossrail.co.uk

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Shaft

Tunnels

Grout injection pipe

Where and when will grout shafts be used? Thorough assessment before the Crossrail works and continuous monitoring during them mean that we can accurately determine where grout shafts are required and when grouting needs to be done.

Most commonly they will be set up in advance of excavation and underground work, at a distance of between 20 and 50 metres from the elements of work that need compensation grouting.

The first grout shafts will be set up in the summer of 2011.

Some shafts will be required for only one phase of work, some for several phases; some will need to be in place for a period beyond completion of the works to control minor long-term settlement. When they are no longer required they will be removed, the shafts backfilled and the ground reinstated.

How can I find out more? If you wish to find out about Crossrail you can contact our Helpdesk on 0345 602 3813. Alternatively, visit our website (www.crossrail.co.uk) where you can find out about ongoing works and sign up to receive regular updates.

More information on our commitment to minimise settlement can be found in the leaflet ‘Your Guide to Ground Settlement’, also available on the Crossrail website at www.crossrail.co.uk/ground-settlement

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IntroductionThis guide will tell you about ground treatment. It will explain:

• why ground treatment is necessary

• what grout shafts are

• how grout shafts will be used on the construction of Crossrail

Why is ground treatment necessary?

Digging tunnels, shafts and basements, such as will be undertaken during the construction of Crossrail, always causes small movements in the ground. This effect is called ‘settlement’. In most cases you would not be able to see the effects of settlement but in some cases there may be small cracks in plaster, and in a few cases doors or windows may stick. Very rarely, settlement can affect the structure of buildings.

Ground treatment works can minimise settlement and its impact on property.

How will Crossrail minimise settlement?

We know a lot about how settlement works in London from projects such as the Heathrow Express Railway, the Jubilee Line Extension, tunnels for the Docklands Light Railway, the Channel Tunnel Rail Link and the Thames Water Ring Main. We have also learned a lot about how best to minimise it.

In the first instance, settlement will be minimised by the tunnelling and excavation

The worksites will be surrounded by hoardings to limit dust and noise emissions. In addition, much of the equipment that will be used will be located within the shafts themselves, further limiting noise and dust.

techniques that will be used on Crossrail(for example, by using tunnelling machines that exert a continuous pressure on the surrounding earth).

In the second instance, if necessary, we will minimise the impact of settlement by treating the ground so that it is less likely to move. The most effective means of doing this is by using ‘compensation grouting’.

What is compensation grouting?Compensation grouting is a well established technique employed on tunnelling projects around the world to minimise settlement.

It works by injecting a cement-like substance, grout, into the ground to firm up the area where settlement is expected to occur. The grout is injected via small-diameter underground pipes which spread out from a central ‘grout shaft’. This method can be employed very precisely and is an effective way of minimising settlement and damage to buildings.

What are grout shafts? Grout shafts are holes in the ground from which grout can be pumped.

They will be operated by small teams (usually between five and ten people) from worksites approximately 30m x 6m in size. When they are not operational these worksites can be reduced in size.

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