Development of a Rockfall Hazard Rating Matrix

Although Ohio is not considered a "mountainous state", it is well documented that rockfalls are prevalent. Rockfalls pose a considerable risk to traffic safety, create maintenance problems, and exert a strain on limited maintenance funds available to the Ohio Department of Transportation (ODOT). In order to assist ODOT in their prioritization for remediation work, a relative rockfall hazard rating matrix has been developed. One hundred eight sites along Ohio roadways were characterized for their geology, geometry and traffic characteristics. As compared to other states where rating systems have previously been developed, Ohio geology can be characterized as relatively flat lying alternating sequences of durable and nondurable sedimentary rocks. Because of this, the matrix focuses on differential weathering and undercutting present at road cuts. Data were collected for all sites and were statistically analyzed, using univariate, bivariate, and cluster analyses, to determine significant variables that characterize slopes. Statistical analyses indicated that slake durability index (SDI), slope angle, and slope height were the most significant variables in differentiating between sites. A matrix was 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 and joint roughness), potential block size, and hydrologic condition. Geometric parameters were evaluated through a comparison of actual field conditions to prescribed Ritchie catchment ditch design. Traffic parameters included average daily traffic, percent decision site distance, and pavement width. Information about rockfall history was unavailable for this research project, but its importance has been well documented. For this reason, a subjective assessment of rockfall history has been included. The matrix assigns scores on an exponential scale based on relative risk, with higher scores representing more of a hazard. The developed matrix was applied to all sites, and scores ranged from 23 to 157. Based on the final scores, three broad-based categories of hazard were developed to more easily characterize the sites (high>100, moderate 50-100, and low<50). The rating matrix can be used to evaluate other rock slopes in Ohio and neighboring states with similar geology. These relative ratings can aid ODOT in making financial decisions and addressing legal issues of slope safety by examination of slopes using engineering principles.

Language

  • English

Media Info

  • Media Type: Print
  • Edition: Final Report
  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 386p

Subject/Index Terms

Filing Info

  • Accession Number: 01004370
  • Record Type: Publication
  • Report/Paper Numbers: FHWA/OH-2005/005
  • Contract Numbers: State Job No. 14782(0)
  • Files: TRIS, USDOT, STATEDOT
  • Created Date: Sep 19 2005 11:36AM