Measurements of effective elastic modulus and microcrack density

Abstract

Effective management of unstable rock slopes on a road network requires knowledge of their location and the risk posed to the road user. Existing stability assessment and risk evaluation systems use variable approaches and are dominated by subjective judgement. In addition they are usually undertaken on a reactive basis, prompted by rock falls. As a consequence road users may be exposed to risk before problems are addressed, comparison of results is difficult, budgetary problems arise as incidents are largely unforeseen, and prioritisation of funds is impossible. In order to address these problems a two stage approach to identifying and classifying rock slope risks has been developed and subjected to field trials. The first stage derives a Rock Slope Hazard Index from rapid, standardised field data collection. The second stage derives a Rock Slope Hazard Rating from detailed field surveys. The trial of the Hazard Index involved assessing 179 rock slopes at a rate of 15 to 20 slopes per man day. The results were used to classify the slopes according to the requirement for future action. The trial of the Hazard Rating involved assessing six slopes and found a total of 75 plane, 27 wedge, 20 toppling potential failures and widespread ravelling.