below ground at T5

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					Mott MacDonald cover story                                                                        www.mottmac.com




Breakthrough on the
Airside Road Tunnel




                             below ground
                             at T5
                             New endings and new beginnings are all in a day’s work for our team at
                             Heathrow’s Terminal 5. As one of BAA’s first-tier integrated suppliers,
                             we’re design engineer for all the £4.2 billion project’s sub-structures and
                             foundations, as well as providing rail assurance services, tunnelling advice
                             and project and programme management. And as our role has drawn to
                             a close on the airside road tunnel, we’ve now entered a busy period on
                             sub-structure design for the terminal’s second satellite building.
10 momentum
                                                                                                              cover story Mott MacDonald




                                                                                                              Five facts on
                                                                                                              Terminal 5


                                                                                                              T5 site covers
                                                                                                              260 hectares –
                                                                                                              equivalent
                                                                                                              to the size of
                                                                                                              London’s Hyde
Heathrow’s 1.3 km long airside road tunnel (ART)       BAA’s contractual framework promotes. It led to        Park.
has a dual purpose – not only providing road           programme savings of over 30 weeks as well as
access from terminals 1, 2 and 3 to Terminal 5, but    improved site safety by avoiding the need to handle
also serving the remote aircraft stands on the         heavy steelwork within confined spaces.
                                                                                                              60 000 people
western edge of the airport from the central
terminal area. This complex job has involved           As work came to an end on the ART, activities have     will be involved
working under one of the world’s busiest airports      picked up on Terminal 5 Phase 2, which includes
                                                                                                              with building
with the challenges of extremely shallow depth and     design and construction of a second satellite
having to pass under existing utilities – and at one   building and 13 new aircraft stands as well as an      T5 over the life
point running only 3 m above the Heathrow              expansion of the baggage and Tracked-Transit-
                                                                                                              of the project.
Express rail link tunnels.                             System housed in tunnels. The satellite building
                                                       has four levels above ground and three levels of
Opened in March, the ART – driven by a 9.16 m          basements up to 18 m below ground. We’ve been
external diameter dual mode tunnel boring              involved since the feasibility stage, with respons-
                                                                                                              It will take
machine – was completed on time and below              ibilities including the design of deep basements for   an estimated
budget and with no impact on the airport’s busy        the satellite building and a number of cut-and-cover
day-to-day operations during the tunnelling            tunnels. By October 2006 we will have delivered
                                                                                                              37 million
process. Trains on the Heathrow Express operated       28 fully integrated design packages and a fully        manhours
as normal and all associated work for monitoring       co-ordinated 3D model.
was able to be undertaken within the normal                                                                   to build.
maintenance closures.                                  Stage one of Phase 2 – currently at production
                                                       design stage with completion scheduled for March
Mott MacDonald has been responsible for the            2008 – includes all the works below ground as well     T5 will have
design of the twin tunnel bores and the approach       as the apron slab and three new aircraft stands,
                                                                                                              175 lifts
structures along with highway design, mechanical       while stage two will deliver the remaining aircraft
and electrical definition design and instrumentation   stands and above-ground building works for live        and 131
and monitoring of this prestigious project.            operation in March 2011. The two stage design
                                                                                                              escalators.
                                                       and construction process creates some unique
Safety was a big focus of our twin tunnel design.      challenges and requires careful planning,
Recognising the need to provide safe access at all     co-ordination and design integration.
                                                                                                              T5 will have
times the decision was taken to bore twin single
carriageway tunnels – but ensure they were             The biggest challenge on the sub-surface works is      the capacity
sufficiently wide to allow vehicles to pass one        the presence of four rail tunnels, three shafts and
another in the case of a simple vehicle breakdown.     three cross-passages. We’ve undertaken detailed
                                                                                                              to serve some
A key innovation was the use of the observational      geotechnical analysis to model the behaviour of the    30 million
method (OM) on the ART portals. With strong            rail tunnels and understand the impact of the
encouragement from BAA, our designers and the          basement design and construction. We’re working
                                                                                                              passengers
civils contractor Laing O’Rourke developed             within strict limits to ensure that tunnel displace-   per year.
substantial time and cost savings in temporary         ments, gradients, distortions and change in lining
works through close teamwork. Based on our             loads meet with specified guidelines. We’ve also
extensive previous experience in the use of OM,        incorporated a deep level chamber for launching
the team saw it as an excellent opportunity for        a tunnel boring machine to construct a baggage
                                                                                                              www.baa.co.uk
innovation and continuous improvement. The             tunnel to the central terminal in the future. We’ve    www.tunnels.mottmac.com

method demands clear communication, commit-            developed the monitoring strategy and will be
ment, and trust between the parties involved           providing construction support until 2008 when the
– totally compatible with the partnering ethos that    first phase of Terminal 5 opens for business.

                                                                                                                           momentum 11

				
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