Design parameters for rockfall protection barriers in the rocks of the Narrabeen Group

The design of effective rockfall protection barriers from first principles can involve detailed site characterisation, extensive trajectory modelling and complex structural design. Alternatively, if the nature of the rockfall hazard can be characterised on the basis of the geological environment, then it is possible select a protection strategy with appropriately specified design considerations. In this paper, a parametric study of rockfall phenomena in areas of the Narrabeen Group is undertaken to determine the likely characteristics of the rockfall hazard that must be managed. Starting with statistical data on the size and shape of the rock debris, and measurements of the coefficients of restitution that are representative of the ground slopes in Narrabeen sandstone environments, a series of rockfall simulations are undertaken for potentially hazardous slopes extracted from the RTA's slope management database. The results present the distribution of energies and trajectories of blocks that are likely to enter road reserves in Narrabeen environments, and they suggest that fences with energy capacities up to 3200kJ, up to 4m high may be required to effectively manage the most severe rockfall risk in these areas. The parameters determined are especially useful in the context of producing a protection fence design that is specifically targeted to being both efficient and effective.