BAA’s £140 million Airside Road Tunnel (ART) was developed as an
improvement to facilities at London’s Heathrow Airport. It
facilitates the transfer of passengers and baggage between the
central terminal area and aircraft stands located on the western
edge of the airport serving the newly opened Terminal 5.
Ramp during constructionThe ART consists
of two bored tunnels each 1.3km long and 8.1m internal diameter
with a further 500m of ramp at each end built as cut-and-cover
structures. The scheme also includes nine emergency escape cross
passages between the two tunnels, two 20m long tunnels for
electrical equipment and two sump facilities built inside the
tunnels. These structures have been constructed using an innovative
one-pass shotcrete lining.
Mott MacDonald Role
TBM cutterheadMott MacDonald was a key
member of the integrated team appointed by BAA to help deliver the
ART. Working with contractors AMEC, Laing O’Rourke Civil
Engineering and Morgan-Vinci JV, our role covered responsibility
for initial planning and feasibility along with preliminary and
detailed design of all works. This included the definition of the
tunnel alignment, approval of tunnel construction methodology to
ensure integrity of the tunnel face, management of the geotechnical
investigation, design of the segmental tunnel lining and design of
the tunnel ventilation system and tunnel services.
Project Highlights
ART bored tunnelThe project demanded
extensive excavation up to 17m deep for the tunnel portals beneath
busy taxiways and aircraft stands while passing above the existing
Piccadilly Line tunnel. Keeping the rail tunnels operational and
minimising disruption above ground were also key requirements
throughout construction. The contractual framework set up by BAA
encouraged innovation and allowed value enhancing alternatives to
be designed and implemented for the tunnel portals. Here, together
with BAA and Laing O’Rourke, we developed an Observational Method
scheme which eliminated the need for temporary steel propping and
overcame severe spatial and logistical constraints.
West portal TBM chamberThe need to
minimise ground settlement caused by excavation through London Clay
at shallow depth below aircraft taxiways, stands and fuel lines led
to use of an earth pressure balance tunneling machine (EPBM) with
the additional provision of compressed air as an alternative method
of supporting the tunnel face. Mott MacDonald experts carried out
the prediction of settlement movements from the tunnel excavation.
To ensure trains could continue to run in the Piccadilly Line and
Heathrow Express tunnels while the construction was carried out
nearby, a real time electronic monitoring scheme was used, its
supply and installation procured from a specialist subcontractor to
manage the monitoring throughout construction.
We also undertook a site surveillance role of the tunnel and civil
engineering works to ensure quality, with specific responsibility
for the minimizing the impact on third parties.
See our dedicated website on Heathrow Terminal 5 ›
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