Highways in Kentucky contain numerous rock slopes and rockfall from these slopes represent potential dangers to motorists. As these highway rock cut slopes age and deteriorate because of weathering, the potential for rockfall and rock slides increases. Some bodily injuries and traffic fatalities have been reported in past years. The general aims of this study were to establish a highway rock cut slope policy and devise a statewide system of dealing with this problem. This study represents the start of an effort by the Kentucky Transportation Cabinet to develop a proactive stance and policy toward preventing, minimizing, or mitigating the rockfall problem on the Cabinet's highways and to establish a rockfall risk management program. As this study shows, the vast majority of rockfall problems in Kentucky occur in counties located east of Interstate 75. Preliminary rockfall hazardous ratings of all rock cut slopes­ – some 5270 slopes – on the Interstates, Parkways, and most Primary routes were performed using the rockfall hazardous rating system (RHRS) devised by Pierson and Vickle of Oregon DOT. This approach appears to be a good system for rating the potential for rockfall at a given highway rock cut location. Some 180 slopes were identified as hazardous. Detailed numerical ratings were performed at those locations. Differential weathering and structural characteristics – jointing and unfavorable orientations – were the major causes of rockfall. Few mitigation measures have been used on Kentucky's highways. For the sedimentary rock strata in Kentucky, benching of rock slopes appears to be very effective in preventing, or mitigating, rockfall on Kentucky's highways. The rock cut slope design guidelines used by the Cabinet appear to be sound. The basic problem is not design standards, but the fact that many of the highway rock slopes are aging, weathering, and deteriorating. With aging, rockfall problems will continue to increase with time. The computer rockfall simulation program devised by Colorado engineers was used to analyze several case studies of rockfall. This program appears to a very good analytical tool for assessing the stability and safety of existing rock slopes and newly designed rock slopes and will be useful in devising remedial and mitigating plans at rockfall sites.

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The contents of this report reflect the views of the authors, who are responsible for the facts and accuracy of the data herein. The contents do not necessarily reflect the official views or policies of the University of Kentucky, Kentucky Transportation Cabinet, nor the Federal Highway Administration. This report does not constitute a standard, specification, or regulation.