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Development of a rockfall hazard rating matrix for the State of Ohio.
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2005-03-01
[PDF-27.58 MB]
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Edition:Final report.
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Abstract: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.
108 sites along Ohio roadways were characterized for their geology, geometry and traffic characteristics. As compared to other
states (Oregon, New York, and Washington) 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 was collected for all sites and was 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
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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 and
joint roughness coefficient), 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 (Pierson, 1991). 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.
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