Lawrence Hargrave Drive SeaCliff Bridge
Wollongong, New South Wales, Australia
The SeaCliff Bridge is the centrepiece of a recent restoration of Lawrence Hargrave Drive, south of Sydney between Clifton and Coalcliff. This section of the coastal road sits at the base of a 300m high rock escarpment which was closed to traffic in 2003 due to the ongoing and unacceptable risk of rockfalls.
The bridge is 665m long combining an insitu balanced cantilever bridge and an incrementally launched bridge with maximum spans of 108m.
The bridge features:
- two traffic lanes with a design speed of 60 kph,
- a three metre wide pedestrian and cycleway on the seaward side
- a 100 year design life (a major challenge with foundations located in a wave zone)
- long-term design durability by application of an active cathodic prevention system.
The balanced cantilever bridge is a curved single-cell post-tensioned box girder with main spans of 108m and variable depth from six metres over the piers to 2.5 metre midspan.
The piers are supported on 1.5 metre diameter bored piles with solid pile caps and hollow pier columns, which in some cases required temporary rock bunds to be placed to facilitate construction access.
The incrementally launched bridge has an overall length of 203m and consists of six 30m spans with a 23m end span on a 150m radius horizontal curve.
The bridge required extensive temporary works to enable construction to be completed in a particularly tight timeframe, including access roads and rock seawalls for the foundations and tower cranes for the balanced cantilever deck.
A curvilinear bridge alignment was chosen to replicate the natural shape of the coastline, with a minimum offset from the existing road of approximately 45m.
The bridge solution took into consideration the foundation conditions along the chosen alignment, including the presence of rock ledges, a two metre thick coal-seam underlying most of the site, a severe wave environment, and restricted construction access conditions.
Associated works included:
- blasting of 3000 cubed metres of rock from the escarpment face,
- extensive mudslide chute and basin constructed with gabions,
- extensive rock bolting, grouting and mesh protection works throughout,
- the structural widening of the road at the edge of a 30m high rock face.
The Sea Cliff Bridge was opened by the Premier of NSW on 11 December 2005, two months ahead of schedule, and has become an icon structure to the people of Wollongong, once again welcoming tens of thousands of tourists annually to this picturesque coastal road.
