Rock slope hazard assessment: a new approach

Abstract

Abstract Uncontrolled bulk blasting and the application of ‘standard’ designs have left a legacy of many unstable highway rock slopes, some of which are potentially hazardous. Effective management of these slopes requires knowledge of their location and the risk posed to the road user. Existing rock slope stability assessment and risk evaluation systems use various approaches to data collection, and different scales and nomenclature for results. In addition, these assessments are usually undertaken on a reactive basis, prompted by rockfalls. As a consequence road users may be exposed to risk before problems are addressed, comparison of results is very difficult, budgetary problems arise as incidents are largely unforeseen, and prioritization of funds is impossible. As a result of a research programme undertaken for the Scottish Office Industry Department (SOID) National Roads Directorate, a new, proactive approach to identifying and classifying rock slope hazards has been developed. Application of this new approach is likely to improve risk management of hazardous rock slopes. The first stage of this approach derives a rock slope hazard index from rapid, standardized field data collection. This is used to classify rock slopes into four categories depending on the requirement for future action. The second stage derives a rock slope hazard rating from detailed field surveys. The rating is a measure of the risk of a vehicle incident being caused by rockfall. The results of a field trial of the rock slope hazard index, carried out on a section of trunk road in the Scottish Highlands, are described.