ACCESS TO CHANNEL ISLAND

The Channel Island access road will provide access from Palermston to Darwin's new coal-fired power station. A number of constraints were placed on the design and construction of this project, with the most critical being the very compressed timetable for completion of the roadway to the Channel Island bridge site, and the performance of that road under heavy construction traffic. A feature of the roadway is a 5.4 km section which traverses tidal islands and mangrove mud up to 7 metres deep. Following detailed analysis of various design alternatives, a novel approach of construction using stone columns was recommended. Installed at closely spaced intervals, the columns penetrated the mangrove mud to the underlying incompressible zone and are designed to provide support for the embankments over the tidal swamps. The system provides much reduced total settlement of the embankment and reduction of the period during which consolidation of the foundation soil would be achieved. By adopting this form of construction, a trouble-free structure was achieved within the construction schedule at a minimum cost penalty in comparison with conventional construction techniques. (Author/TRRL)