Stormwater Upgrade and Road Reconstruction

Thursday, 6 August 2020

Council commenced a project to replace the 70 year old stormwater pipe in Gray Street, Riverside which was cracking and losing shape, to enable it to service the current and future needs of the area.

The project was undertaken in three stages over three years, after excavation works uncovered underground conditions that were far worse than expected or had been encountered in previous stages. 

The ground condition under the road was found to be a soft, saturated clay “slurry”.  Therefore the entire road of approximately 350 metres had to be reconstructed by digging out existing materials to a depth of 600mm, removing it from the site, and replacing it with new compacted fill and geotextile fabric as can be seen in Hudson Civil Products' images attached.

Contractors, Zanetto Civil, used ‘Geofabrics’ E’GRID GT3030 with an attached geotextile layer to provide both tensile strength and separation for drainage and pavement layers.  This is made up of a biaxial geogrid laminated to a nonwoven geotextile and is widely used in subgrade improvement and pavement strengthening works in Tasmania. 

Inside the geotextile surround, graded rocks less than 150mm in diameter were used to enable drainage, with the water directed into the existing stormwater system via HDPE piping. This was required to provide a solid structure to position the stormwater pipe within and allow for the road to be reconstructed above it. 

Council in its 2019/2020 Capital budget allocated funding to reseal the entire length of Gray Street with asphalt. Work was unable to be undertaken until a dry sub base was achieved.

The road surface is built to last with a 30 year design life, and associated stormwater infrastructure is now of a high standard and capacity.

Traffic flow and access for local residents was maintained during the entirety of the project and we appreciate their patience and cooperation during the entirety of the project.