Low impact marine construction

On the Granite Island Causeway Project in South Australia our team used the 'hand over hand' construction method to minimise environmental impacts and ensure delivery on time.

The 'hand over hand' method employs three concurrent work fronts:

  • Front one installing the permanent piles
  • Front two installing the grouted HDPE sleeves and the precast headstocks
  • Front three installing the precast longitudinal girders and decks. 

As the structure advances out into the water it acts as a construction platform for the work crews to build the next stage. Each work front takes a similar duration, ensuring maximum productivity.  

Analysis was conducted on various construction approaches during the tender phase, including the use of jack-up barges or a temporary bridge structure to facilitate construction. However, the 'hand over hand' method was the only one capable of achieving completion by the target date. 

The other benefit of the method is its minimal footprint. Minimising the impact on the sensitive marine environment was a key consideration during the tender and design phases of the project. 

The adoption of the method, along with the use of precast prestressed deck units which pushed the span out as far as possible, minimised the number of pile driving operations further reducing the impact on the marine environment.  

The design and construction methodology was fit-for-purpose and extremely efficient. It resulted in on time and on budget completion and had a low impact on Victor Harbor's rich marine ecology.