Since the Kings Highway was first constructed, the Clyde Mountain area has been subject to landslips affecting transport to and from the South Coast, with landslips strongly correlated to high rainfall events. Following a landslip which closed the Kings Highway for 6 days in 2012, RMS engaged a geologist to produce an options report to reduce slope risk at Clyde Mountain on the Kings Highway.
The large rock slide of approximately 930 m3 or 1600 tonnes completely blocked MR51 Kings Highway between Batemans Bay and Canberra on Clyde Mountain 25Km east of Braidwood. The slide demolished part of the existing large rockfall fence as well as other provisions. The rockslide was quickly cleared by Eurobodalla Council workers and a temporary fence was installed. The catastrophic nature of the rock slide, the existing mitigation measures and the existing risk assessment relying on measures being designed to prevent failure, all contributed to an unprecedented failure.
NSW Public Works were engaged to provide quality project management services to RMS to refine and implement the options to reduce the slope risk. From the outset of the project, the NSW Public Works team worked closely with RMS to establish a clear scope of works and a communication strategy for all stakeholders.
Stage 1 works were to remove vegetation via hand and machine scaling to reduce significant immediate risks. Stage 1 works allowed for the refinement of the design to enable a permanent engineered geotechnical risk reduction solution.
Stage 2 works saw the installation of the refined design in the areas cleared under the stage 1 works and included the installation of rock bolts, enhancement of rock catch fences, shotcrete and rock fall mesh. The expertise of the key project management staff involved in the project complimented by their experience in similar projects and their understanding of the local community contributed to more frequent access of the Kings Highway during stage two works construction and with greater level of safety.
The evaluation showed a significant reduction in the risk levels associated with the site. It also highlighted further down slope risks that were indicated by the drilling conditions encountered during the works.