Context :

The Mooney Mooney Creek subcatchment, in the Hawkesbury Estuary, is largely dominated by bushland and is subject to long-term sustainability and bank erosion issues. During the torrential rains of June 2007, a steel road culvert collapsed on the Pacific Highway when the roadway embankment failed.


The problem :

Owing to the significant consequences of this rupture and to local media attention, the Gosford City Council was in need of an urgent and viable solution to replace the collapsed culvert. An inspection of other similar structures in the catchment area found that a steel culvert at Leask Creek also needed to be replaced.

The Gosford City Council required concrete culverts, with concrete headwalls that could be tailored to suit the site requirements.


The solution :

The design and supply of the replacement culverts were awarded to the Reinforced Earth Company (RECO). Based on RECO's experience, the customer was confident of its ability to rapidly install an efficient prefabricated arch system. The presence of a local company, with installations nearby, was an additional advantage.

RECO was able to supply durable and high-quality TechSpan® precast arches using moulds from a previous job, which were cleaned and slightly modified to meet the particular design requirements of the new culverts.

One of TechSpan's® major advantages is that it can be adapted to suit specific project requirements. The TechSpan® precast concrete arch system can be seamlessly combined with concrete-faced Reinforced Earth retaining walls, adapted to receive special finishes to satisfy aesthetic requirements. The interface of these two systems is accomplished through precise arch and panel fabrication, marrying each panel to the shape of the arch. Precise casing of each arch ensures a proper fit between units. Scheduling was the biggest challenge for this project due to tight time limits between precasting and delivery owing to the sensitive nature of the project and given the amount of public attention. In addition to all that, delivery was complicated by the thoroughness of site preparation where rock levels had to be adjusted so that the storm water would flow exactly according to the design.