Development of a strategic slope management system for use in South Africa

Abstract

Despite some preliminary developments for Slope Management Systems (SMS) for the South African Road Network, no functional SMS has been implemented. Slopes along important strategic routes are generally not monitored and only maintained on a reactive basis. This application of remedial measures after failures occur often results in disruptions to the flow of traffic. The USA is the leading implementer of Rock Hazard Rating Systems (RHRS) and bases these systems on qualitative methods that follow a heuristic approach. The first state wide RHRS was developed in Oregon and awarded scores to various categories that contribute to rockfalls and the potential impact thereof on traffic. This RHRS has been adopted by 18 different states either unchanged or modified to suit the local conditions. Unstable slopes need to be reassessed every 2 years, or before maintenance budget allocations, to allow for the RHRS inventory to be updated and mitigation plans to be made. There is, however, limited literature available on comprehensive SMS’s that incorporate both rock and soil slopes. Following a comprehensive literature review the modified Colorado Department of Transport RHRS was found to be a suitable starting point for the development of a SMS for South Africa. As the system contains no rating methodology for soil slopes, appropriate rating criteria have been incorporated into the proposed South African system. Other modifications include the removal of variables considered unimportant in South Africa and the variables concerned with the risk to lives of motorists. The proposed method is intended to be applied on an iterative basis with initial basic observations of all slopes along a route and proceeding to different levels of reassessment on specific slopes based on the identification of high risk slopes. The method has been used on major road links of an important strategic nature within South Africa to asses its suitability