Greens Road Flood Repair – MagnumStone™
Hawkesbury City Council
Pells Sullivan Meynink
Greens Road, Lower Portland, NSW
In March 2021, severe flooding along the Hawkesbury River, north of Sydney, caused significant damage to two sections of Greens Road in the Lower Portland Region. This made for a very challenging time for the residents. With many homes requiring repair works due to damage caused by the flood event, access to many residents’ properties was limited to a fire trail. In some cases, the lack of suitable infrastructure meant it was unsafe to return to their homes at all.
From the beginning, Greens Road was identified as an extremely challenging project. Access into the site could only be gained from one end of the project, but weight restrictions imposed along this long, narrow track meant that construction of the required retaining structure needed to be fast and easy to install using small, compact equipment. It needed to withstand future flood events and allow construction to be staged while giving temporary all-weather access to the residents.
To successfully overcome these challenges, two significant retaining structures along separate 350m and 360m sections of the road alignment were designed. Ranging from 1m to 6m in constructed height, the design used the MagnumStone positive connection system with StrataGrid geogrid straps. Significant anchoring and erosion protection was also designed for the slopes above.
Due to the proximity of the river, the walls will become fully submerged during future flood events. To provide a robust design preventing erosion of the toe and the effects from rapid draw down, the MagnumStone units were placed on a concrete footing directly on bedrock. The hollow core of the MagnumStone units was then filled with 20mm drainage chip. This provided a free draining channel at the face of the wall.
The MagnumStone system also allowed staged construction. Because MagnumStone blocks are precast, there’s no waiting time for curing. Once StrataGrid had been laid and the structurally engineered sandstone compacted behind it, heavier vehicles could use the road, opening previously inaccessible areas of the site.
Further flooding, unexpected soil conditions and the creation of temporary accessways for both construction and residents meant the Greens Road project had a very tight program. Cirtex’s challenge was to get the blocks scheduled and produced on time. Delaney’s challenge was delivering the large number of blocks onto the narrow site. Because the work platform was also the site access, transporting over 4,100 MagnumStone blocks and 55,000 lineal meters of StrataGrid geogrid reinforcement onto the site often required double and triple handling of the material.
Delaney Civil also performed night works to meet the program, enabling specified times during the day for construction and residential access. Once prepared, Delaney Civil found the MagnumStone system consistent, easy to lay and very easy to work with. MagnumStone’s design was easily adapted to follow the alignment of the road. All curves were created without cutting or trimming blocks, maintaining a secure lug connection between all the units in the construction.
Cirtex is pleased to have worked with Delaney Civil on this challenge project and we value the opportunity of providing the local community with unrestricted, robust and all weather access to their properties.
The MagnumStone system provided the following benefits to the project:
- Large quantities delivered quickly to site
- Resists rapid draw down effects
- Able to be installed in narrow conditions