The hazard of falling rocks is a significant issue for transportation infrastructure providers in areas of steep topography. This paper presents the results of a survey undertaken to characterize the nature of the rocks that might fall to create a rockfall hazard in the Tertiary basalt environments of eastern Australia. It finds that the size of jointformed fragments in intact rock masses varies up to around 0.6 m, but that subsequent fragmentation and chemical breakdown during weathering is likely to reduce the average size to around 0.3 m. The maximum size of a likely falling rock is around 0.4 m. Fragments of basalt may occur in a variety of basic geometric forms, reflecting their strongly jointed origin, but their low resistance to chemical weathering causes them to become rounded. The tendency toward roundness is exacerbated by the presence of vesicles and ultramafic xenoliths, where these occur. It is also observed that natural slopes in basalt areas tend to become rockier as their steepness increases, making size more important than roundness for blocks on steeper slopes. These characteristics have consequences for the ability of fragments to continue rolling once a falling motion is initiated, and hence, for the geometric characteristics adopted when evaluating rockfall hazards in basalt using numerical simulations.
11th International Association of Engineering Geology Congress, 2010 (IAEG2010). Proceedings of the 11th International Association of Engineering Geology Congress 2010 (Auckland, New Zealand 5-10 September, 2010 ) p. 2899-2907