Picnic Point Sea Wall
The sandstone sea wall at Picnic Point on the Sunshine Coast at Maroochydore was crumbling away, leaving a series of sink holes and broken rocks exposed to passers-by. Sunshine Coast Regional Council chose Hanson’s Glasshouse Quarry Armour Rock to replace the falling sea wall because its high-quality stone met strict petrographic and engineering specifications.
Armour Rock as tough as armour
The Glasshouse rock is classed as welded-tuff or ‘Ignimbrite’, which comes from the Latin for ‘fire’ and ‘storm cloud’. It’s a durable volcanic rock consisting mostly of consolidated pumice fragments. Glasshouse Quarry produces dark grey Ignimbrite with attractive ochre, green, and deep red colourations, that blends well into the natural landscape at Picnic Point. The Sunshine Coast Regional Council team selected a mixture of 600-800mm Armour Rock, along with P5 and P3 class stone, to rebuild the wall. Rocks are selected manually, and moved into position along the length of the wall, then secured with a slurry mixture. The front, sea-facing sides of the stone are hand-grouted by a specialist team to ensure there is no movement or slippage. The rear side of the wall is stabilised with 20-40mm drainage material, also supplied from Glasshouse Quarry.
Tides pose challenges to Armour Rock build
The Picnic Point worksite has picturesque views of the Maroochy River and a relaxing ambiance, but the sought-after water frontage has made for a difficult build. According to site manager Dennis Smith, one of the main challenges faced by the council in completing this job was managing the work schedule around the changing tides. “Some days there were six available work hours and other days there were none at all - particularly during the king tide”. The river rose and completely covered the working face of the wall making progress impossible. To help, Hanson maintained a moderate stockpile of Armour Rock on site allowing the council to make their tide-bound schedule more productive. By making sure there was always product to hand the council team were able to work whenever the tide allowed. Work on the sea wall began in late 2017 and the Picnic Point section was completed in March 2018. Later this year the same process will begin on the sea wall at Golden Beach.