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Design and Construction of Tunnels for Northern Gateway Project, New Zealand


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Author D Sykes, B D Hegan and M Behrens and A McPhee


This paper describes the design and construction of twin 400 m long road
tunnels as part of the Northern Motorway Extension Project in Auckland, New
Zealand. Construction of the tunnel civil works is now completed and
installation of mechanical and electrical systems is well underway. The tunnels
are expected to be open for traffic at the end of 2008.

The paper will address the design aspects of the project including: tunnel
alignment and cross-section, geotechnical conditions and rock support,
waterproofing and concrete lining and fire and life safety. The paper will cover
the bored tunnel section, the cut-and-cover tunnel section, cross passages and
portal structures. The design brief included a requirement for the tunnels to be
a gateway to Auckland and this required particular attention to be given to the
visual appearance of the finished tunnel structure. The final arrangement of the
portal structures and a requirement for recesses in the concrete lining for
emergency cabinets, deluge pipework and cable runs, reflects these

The tunnels were excavated by a roadheader and road planer using a heading
and bench. Initial support was provided by a combination of lattice girders,
cement grouted rock bolts and steel fibre reinforced shotcrete. The permanent
lining consisted of installation of a drainage geotextile and waterproof
membrane, followed by cast in situ unreinforced concrete. Each portal consists
of a cut-and-cover section. This paper describes the tunnel construction
methods, including the particular requirements for safety, the environment and
community relations.

The tunnel is fitted with a compartmentalised deluge system for fire fighting
purposes. The tunnel control centre is incorporated into the control centre for
Auckland Harbour Bridge, some 30 km from the tunnel location.