Rockfall risk and remediation on the Lake George Escarpment

Andrew Hunter, Tom Nicholson, Peter Burgess and Val Brizga

In 2005 a rockfall occurred on the Lake George Escarpment, north of Canberra in New South Wales causing rocks to be strewn across the Federal Highway. Although vehicles were not hit by the fall, a significant traffic accident ensued as vehicles attempted to avoid the debris on the highway. The escarpment had not been previously recognised as a site prone to rockfall with no recorded or published history of rockfalls. A subsequent investigation involved the use of photogrammetry, geomorphological and geotechnical mapping, and computer rockfall simulations to assess both the extent of rockfall hazard across the escarpment and the risk to road users. The assessed risks at the site exceeded the tolerable risk level stipulated by the NSW Roads and Traffic Authority (RTA). Slope remediation works involved the partial removal of the rockfall hazards by blasting and manual removal in conjunction with the construction of a series of rockfall fences to reduce rockfall risk to tolerable levels. This paper provides a commentary on rockfall trials filmed with high-speed motion cameras that were conducted to calibrate rockfall simulation software and assess the fence requirements. The paper also provides insight into natural hazards with the potential to affect transport corridors that should be considered at route selection stage.