Slope strategy for Pearl Beach Dr

A strategy on slope stability risk reduction for Pearl Beach Dr, Pearl Beach, has been recommended for adoption by Gosford Council.

Council officers have recommended that the strategy by Shirley Consulting Engineers be adopted.

The geotechnical report and Slope Stability Risk Assessment prepared by the consultant covered issues including the risk of rockfall onto the road, risk of damage or failure of the road pavement and other infrastructure and risk of landslip or rockfall from the embankment below the road formation.

It also covered issues about areas vulnerable to potential landslip or rockfall hazards including traffic and road users, road and utility infrastructure, and private property below the road formation.

The report recommended six actions to reduce the risks to "an acceptable level" or alternative risk treatments.

It stated: "A detailed survey be prepared of Pearl Beach Dr, including the road reserve and private land boundaries, road alignment/width, reduced levels on cuttings and spot heights/contours on slopes."

The survey would particularly focus on obtaining information in the critical remedial works areas.

The recommended: "Council's development section be advised of the various risks posed to the private properties in Jade Place (both by Pearl Beach Dr and from within the private land), and independent risk assessments be carried out of the various properties in Jade Place as part of the risk reduction program in Pearl Beach Dr.

"A 'concept design' of the necessary risk reduction and remedial works be prepared and the costs of the necessary repair works be more accurately determined.

"The detailed remedial works design be verified by an experienced geotechnical engineer, before the works are carried out at the site.

"During construction of the various remedial works, inspections be carried out by an experienced geotechnical engineer, to identify and confirm foundations materials, seepage sources, drainage collection and disposal methods and temporary support/stability of excavations.

"On completion of the remedial works program, an updated risk assessment be prepared for Pearl Beach Dr to confirm that the various levels of risk have been reduced to acceptable levels."

Council officers said they would "immediately proceed" with the first three recommendations, and then proceed to the other three.

The remedial works were divided into several sections.

The first involved the widening of Pearl Beach Dr on the cut side of the road to provide for drainage and sufficient shoulder width to act as a catch area for minor rock falls from the slope above.

It also involved the general scaling of the excavated rock slope, the installation of a number of rock bolts and the stabilization and removal of some of the boulders on the slope above the road excavation.

Some landscaping and revegetation would also be included.

Other parts of the remedial works included the construction of a trench drain on the cut side of the road excavation, to intercept overland and seepage flows from the hillslope above, along with piping and channelling of the flows in to a drainage system.

It would also include the repair of the existing damage and leaky pipe culverts that transverse the roadway along with the reconstruction of the pavement in the areas that are currently significantly damaged, and areas of the road pavement likely to be damaged during the course of the remedial works.

Council has applied for funding assistance for road stabilisation works in Pearl Beach Dr from the Federal and State Government funded 2007/08 Natural Disaster Mitigation Program up to $150,000.

The funding is conditional upon council contributing a further $75,000.

A council report stated that the application was still under review and had originally been anticipated to be determined by July.

It stated that: "Should the application be approved some of this funding could be used to scale, bolt or anchor some of the loose rock material above the slope under the supervision of a geotechnical engineer without the need for detailed design, as has been carried out nearby at Patonga Dr, Pearl Beach".

Council agenda CIT.26, 4 Sep 2007