Infrastructure - New Lynn Rail Trench
Going underground requires concrete expertise
In April 2008 Firth began work on the New Lynn Rail Trench. One of the most technically challenging parts of Project DART, a $600m upgrade of Auckland’s rail network, it meant lowering a 1km of track into an open cut trench. Requiring approximately 50,000m³ of concrete in total, the rail trench is the most significant concrete project currently underway in New Zealand.The process involves creating a diaphragm wall from a specialist tremmie mix of concrete on each side of the new rail trench, which initially acts as a retaining wall. Once the sidewalls are complete then the concrete slab for the bottom of the trench is poured last.
Firth worked with the Rail trench team to develop an appropriate range of concrete mixes. A number of considerations were important for differing applications including early strength/low heat requirements. “Firth offered technical leadership and concrete expertise to the operation,” says Marc Hainen, Chief Operating Officer Firth Northern.
The redevelopment will mean improved public safety, traffic movements and station facilities. However the new rail trench is still on a working railway in a congested traffic area and that brought it’s own challenges.
“Operationally, the new trench is on a live rail line in a busy transport centre so we have had to work around that and much of the work has had to be done at night,” says Hainen. “Firth is lucky that it is allowed to operate 24 hours a day, so the majority of the concrete is delivered at night. The tremmie mix is poured on a night shift to avoid traffic and congestion,” he says.
Once the trench is completed, the main rail track will be moved into it and bridges will be built over the tracks, so the rail line will be underground – which is much safer than the current situation where a main rail track passes through a busy centre.
Firth expects the project will be completed by mid 2010. back to top