Development of a Rockfall Hazard Rating Matrix for the State of Ohio

Final report.PDFTech ReportFHWA/OH-2005/005State Job No. 14782RockfallsLandslidesHazardsHazard analysisHazard evaluationRatingsMatrices (Mathematics)OhioOhio. Dept. of TransportationShakoor, AbdulWoodward, Martin J.Kent State University. Dept. of GeologyOhio. Dept. of TransportationNTL-ENERGY AND ENVIRONMENT-Environment ImpactsNTL-HIGHWAY/ROAD TRANSPORTATION-Soils and GeologyUS Transportation CollectionAlthough Ohio is not considered a "mountainous state", it is well documented that rockfalls are prevalent. Rockfalls pose aconsiderable risk to traffic safety, create maintenance problems, and exert a strain on limited maintenance funds available to theOhio Department of Transportation (ODOT). In order to assist ODOT in their prioritization for remediation work, a relative rockfallhazard rating matrix has been developed.108 sites along Ohio roadways were characterized for their geology, geometry and traffic characteristics. As compared to otherstates (Oregon, New York, and Washington) where rating systems have previously been developed, Ohio geology can becharacterized as relatively flat lying alternating sequences of durable and nondurable sedimentary rocks. Because of this, thematrix focuses on differential weathering and undercutting present at road cuts.Data was collected for all sites and was statistically analyzed, using univariate, bivariate, and cluster analyses, to determinesignificant variables that characterize slopes. Statistical analyses indicated that slake durability index (SDI), slope angle, andslope height were the most significant variables in differentiating between sites.A matrix was then developed based on the statistical analysis and information gained from previously developed rating systems.Geologic parameters include geologic conditions (SDI and maximum amount of undercutting; discontinuity extent/orientation andjoint roughness coefficient), potential block size, and hydrologic condition. Geometric parameters were evaluated through acomparison of actual field conditions to prescribed Ritchie catchment ditch design. Traffic parameters included average dailytraffic, percent decision site distance, and pavement width. Information about rockfall history was unavailable for this researchproject, but its importance has been well documented (Pierson, 1991). For this reason, a subjective assessment of rockfall historyhas been included.The matrix assigns scores on an exponential scale based on relative risk, with higher scores representing more of a hazard. Thedeveloped matrix was applied to all sites, and scores ranged from 23 to 157. Based on the final scores, three broad-basedcategories of hazard were developed to more easily characterize the sites (high>100, moderate 50-100, and low