Cardno-Designed Stormwater Structure Withstands Wild Weather
When a heavy storm struck Sydney on the first weekend in June, huge waves and king tides resulted in erosion of the beach and damage to properties at Collaroy.
During this event, a stormwater pipe designed by Cardno escaped damage, one of the few structures in the vicinity to emerge unscathed.
Between 2011 and 2015, a multi-disciplinary Cardno team worked on improving and extending the 85m pipe, which had become a safety hazard from continual wave and tidal impacts due to failure of the structural components. Our services included concept design, survey, geotechnical and utility services investigations, water quality analysis, flood modelling, community consultation, structural construction documentation and cost estimation.
Structural aspects of Cardno’s work were completed by Senior Principal Kevin Leedow and structural design engineer Peter Whelan. Senior civil engineer Rob Lenferna completed the civil components, while coastal, ocean and estuarine expert Doug Treloar undertook the coastal modelling and wave loading on the structure. The coastal modelling anticipated the extent of potential scouring under the structure and local scour around the piles.
Cardno’s design included a narrower outlet structure with a “V” shaped base and rounded face that dissipates forces from incoming waves, especially the uplift forces which lead to the failure of the previous pipe system. The previous structure had a 3.5m wide flat base, which presented a risk to swimmers being swept underneath and not being able to find the surface.
The new structural components were founded on straight and raking concrete piles socketed in rock 20 metres below the surface. The design allows for precast concrete units to be manufactured offsite and craned into position, minimising on-site construction time and associated weather, tidal and wave risks.