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Recent Advances from the United Kingdom Tunnelling Industry – The A3 Hindhead Project

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Author T Ireland and T Rock
ID P200803032

Description

This paper looks at recent advances in the United Kingdom (UK) tunnelling
industry with particular reference to the A3 Hindhead Project. A 1.8 km long
twin bore tunnel is the centrepiece of the A3 Hindhead scheme, which commenced
construction in 2007 and is being delivered under a UK Highways Agency early
contractor involvement (ECI) contract.


The proposed construction methodology is progressive mechanical excavation of
a horseshoe-shaped tunnel with shotcrete installed close behind the face using
robotic spraying equipment. The tunnelling medium is a ‘soft rock' sandstone for
which there was little previous tunnelling experience, requiring extensive
geotechnical investigations and an innovative approach to lining design. A 240 m
long section though sandy material utilising a steel pipe umbrella is also
required.


This paper describes the development of the tunnel planning and
design including the most recent developments in UK road tunnels. The innovative
approach to the design of the following is discussed:

  • the ‘permanent' primary lining,
  • an observational technique allowing optimisation of the steel pipe
    umbrella design,

  • a plain concrete secondary lining designed for resistance to
    a hydrocarbon fire, and

  • a spray-applied membrane.