The F3 Freeway forms the primary road connection between Sydney and Newcastle. It is widely recognised as one of the most scenic in Australia with a series of high vertical sandstone cuttings alternate with open sections providing spectacular long distance panoramic views across forest covered valleys associated with the Hawkesbury River. The high volume of traffic travelling along the F3 combined with its very high scenic values results in a high level of scrutiny of potential visual impacts that may result from road works and maintenance.
Consequently we were engaged by Jacobs on behalf of NSW Roads and Maritime to carry out a visual assessment of proposed rock cut stabilisation works along a section of the F3 Freeway immediately south of the Hawkesbury River Bridge at Brooklyn. The proposed works involved installation of steel mesh over part of the rock cut to control rock fall.
Location: Brooklyn NSW Australia
Images: Corkery Consulting
The visually prominent sandstone rock cuts present a risk to motorists from rocks falling on the roadway. The potential for rock fall results from the combination of rock fractures, weathering of joints and establishment of vegetation results in small rocks being dislodged.
Minimising the risk requires on-going maintenance activities that involve regular inspections, removal of loose rock and vegetation together with the application of ‘shotcrete’ and rock bolting in some situations. These activities result in exposure of fresh rock faces together with areas of fresh ‘shotcrete’ that are visually prominent due to the colour contrast with the adjoining areas of weathered rock.
In order to reduce the cost ongoing maintenance required the Engineering Technology Branch of Roads and Maritime Services (RMS) proposed to install high-tensile steel rock fall mesh along a number of rock cuts. The mesh is intended to amount of work required to treat the rock cut and extend the period between maintenance events.
We carried out a Landscape Character and Visual Impact Assessment of the proposed mesh installation for a series of rock cuts along the F3 Freeway. The assessment predicted that the proposed installation of mesh would result in a moderate to high visual impact. However, there was varying opinion about the magnitude of visual impact.
Consequently RMS agreed to install a trial section of the proposed mesh on a portion of rock cut so that the potential visual impact would be more accurately predicted. The trial included the application of various paint colours to sections of the mesh to test the level of visual impact mitigation that they achieved.
Results of the trial confirmed that painting the mesh black resulted in a significant reduction in the level of visual impact on motorists travelling along the F3. Consequently the permanent mesh, which has been installed to reduce the risk of rock fall along a number of rock cuts, is powder coated in black.