The New Lynn Rail trench formed the largest component of KiwiRail’s Project DART, a major upgrade to the Auckland rail network, duplicating the track to allow for increased train frequency to meet passenger demand.
The project was integral to key stakeholder Waitakere City's New Lynn Transit Oriented Development (TOD) vision to improve vehicle, pedestrian and cycle movements around New Lynn as part of urban renewal of the town centre.
In conjunction with contractor Fletcher Construction with specialist partners and Synergine and Parsons Brinckerhoff, Beca was commissioned to design the New Lynn Rail Trench and associated lowering and road bridging of a duplicated rail track.
The rail trench was constructed using the diaphragm wall technique top down, bottom up method of construction, the first of its scale in New Zealand. 1.5km of the Western Line was duplicated and lowered into a new, up to 8m deep, 880m long trench, in which sits the 225m central platform.
Some 100,000m3 of earth was removed and 60,000m3 of concrete used in the diaphragm retaining wall and trench base slab construction. An innovative methodology of track slews and relocation of the operating track onto the northern diaphragm wall whilst constructing the balance of the trench and the base slab allowed road and rail operations to be maintained throughout. The rail trench project also included four new overbridges and a new level crossing.
Beca provided geotechnical, structural, civil, hydrogeology, survey, traffic engineering, building services and fire life safety design and construction supervision for the project.
Beca also completed the structural and building services design for the enhanced station commissioned by ARTA. The concourse involved four inverted pyramid canopy structures, glass clad walls, ticketing and passenger waiting areas connected by stairs, lifts and escalators to the platform, creating a signature interchange for Auckland’s third busiest rail station.
Beca was also commissioned by Waitakere City to design the upgrades and modifications to the local roads made possible by the rail trench. Beca Planning managed the consenting process to obtain all the necessary approvals to support the design works, including securing a new road designation over the rail corridor.
The collaborative working relationship with key stakeholders and early contractor involvement (ECI) contract procurement model with KiwiRail and Fletcher successfully achieved early enabling works to start, an optimised design, and project delivery early and within budget. March 2010 saw the first train through the trench, and the new belowground rail station and above ground bus interchange and street network opened to the public mid-September 2010.