Rockfall Hazard Classification and Mitigation System

Abstract

The Montana Department of Transportation (MDT) Rockfall Hazard Classification and Mitigation System research project was initiated in February 2003. Once customized for MDT conditions, the Rockfall Hazard Rating System (RHRS), a nationally recognized rock slope management tool, was selected for implementation in order to provide the information MDT needed to make informed decisions on where to invest safety dollars at rockfall-related locations. An initial review of the highway system using MDT's Transportation Information System (TIS) ImageViewer was completed. Roughly 2,600 potential rockfall sites were identified. Using a web-based questionnaire, rockfall history and behavior information was gathered for each site from the local maintenance person responsible for the affected portion of roadway. Preliminary Rating was performed on each identified site. In all, 2,653 sites were visited resulting in 1,869 sites being categorized as either A or B sites, indicating a potential to produce a hazardous rockfall situation. The remaining sites that were deemed to pose no or a very low threat of a hazardous situation occurring were eliminated from further consideration. The Detailed Ratings were conducted at the 869 A sites. Once the Detailed Ratings were completed, and based on a decision by the MDT Technical Advisory Committee (TAC), only those sites that received a Detailed Rating score greater than 350 points were categorized as A-rated sites. The resulting database contains 368 A-rated sites. The top 100 A rated sites, those with a score greater than 471 points, were further evaluated and had preliminary designs and cost estimates prepared. The designs included only those elements directly associated with rockfall mitigation. This information will allow MDT to include cost and associated benefits as they proceed with development of rockfall mitigation projects.