Rockfall Hazard Process Assessment: Final Project Report
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2017-10-01
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Edition:Final Report, June 2015 - September 2017
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Abstract:After a decade of using the Rockfall Hazard Rating System (RHRS), the Montana Department of Transportation (MDT) sought a reassessment of their rockfall hazard evaluation process. Their prior system was a slightly modified version of the RHRS and was implemented in 2005. This reassessment included an update of their existing rockfall database, review of developments in slope management systems, and a set of implementation tools to help guide their decision making and project development process. The new MDT Rock Slope Asset Management Program (RAMP) includes a number of new enhancements. RHRS score components have been recombined to create sub-scores to isolate specific evaluation attributes. The slope's Condition is calculated as a function of rockfall history and ditch effectiveness and scored using a 100 (good, like new condition) to 0 (poor or failed condition) linear score. Five new Condition State categories facilitate deterioration modeling and risk analysis. Evaluation of rockfall event records will allow estimation of rockfall event likelihoods based on slope dimensions and condition for use in risk calculations. Programmatic cost estimates to improve the slope, also based on slope dimension and condition, allow rapid network-wide estimation of improvement costs. Performance Measures and Decision Support Tools help guide the planning process. Tools that leverage MDT's cloud-based GIS services permit collection of rockfall events and maintenance activities across multiple computing platforms. Fiscal analyses indicate that the 997 inventoried and assessed rock slope assets represent a value of approximately 4 billion dollars to build again today; a value worthy of notice. Unchecked slope deterioration limits an average slope’s life span to approximately 104 years. A 'Good' condition slope has a 50% likelihood of deteriorating to 'Fair' in 36 years, with another 41 years to deteriorate further to a 'Poor' condition slope. Getting slopes that have deteriorated back to a modern, state-of-the-practice, 'Good' condition would require approximately 700 million dollars. Including slope preservation efforts into a funding plan that maintains network conditions rather than relying solely on comprehensive reconstruction efforts can save MDT 19% for the same outcome, or $7 million dollars annually for a fully funded Rock Slope Asset Management Program.
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