Bridges

The Granite Island Causeway is a key piece of South Australian infrastructure of cultural and heritage significance. It is an iconic landmark for local tourism, used for the historic horse drawn tram services and for recreational pedestrian and fishing activities. It is also the only link connecting Granite Island with the mainland at Victor Harbor, providing access for vehicles that service the island. The existing timber causeway was at the end of its useful service life, having already undergone numerous repairs to address storm damage and natural deterioration. A feasibility study identified that an upgrade of the structure was not viable, warranting full replacement. Key features of the $43 million project include a new 620 m long causeway; boat landing facility; new track and tram stops; foreshore urban design improvements including viewing areas, historic storytelling and interpretive signage, and public art viewing areas; and existing causeway partial rehabilitation and demolition works.

This paper will focus on some of the key challenges and considerations for the design and construction of the new causeway. The geometric and structural designs were heavily dictated by the leap-frog span by span construction methodology, temporary works and craneage limits. Crane demobilisation off the completed causeway was also critical. The construction program precluded the use of in situ concrete works, demanding a fully precast system. This presented several challenges, including development of critical pile to headstock connections without in situ concrete; mitigating girder hog and differential hog deflections; and a high level of coordination between precast manufacturer and post-installed direct fix track. Sustainable materials and solutions were paramount in the offshore environment where inspection and maintenance access is limited. Innovations included FRP balustrading, developed in close consultation with the supplier; 'sacrificial' reinforcement cage to protect the girder primary reinforcing strands; and bearings that don't require replacement.