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.