VERMONT'S ROCKFALL HAZARD RATING SYSTEM

Rockfall is a form of hazard that can have significant unfavorable impacts to the travelling public such as prolonged road closures, damage to property, and loss of life. Roadway construction throughout Vermont, across rough terrain, has required excavation and creation of many rock cuts, which can extend for over thousands of feet and range in height from fifty to over one hundred feet in height. Due to deterioration of the rock cuts over time, unfavorable geologic structures, and relatively steep slopes, rockfalls are an annual occurrence throughout Vermont.

In order to proactively react to rockfalls and to prevent future rockfalls, the Vermont Agency of Transportation (VTrans) has adopted and modified a Rockfall Hazard Rating System (RHRS) that is similar to one developed by the Federal Highway Administration (FHWA) and other DOTs.

The VTrans RHRS consists of criteria that ranks and evaluates these rock cuts on their potential to produce rockfall and likelihood for the falling rock to reach the roadway. Rock cuts are assigned a ranking (A, B+, B, or C), which corresponds to how likely rockfall is to happen at the rock cut and reach the roadway. Current RHRS inventory for Vermont consists of 122 “A” ranked rock cuts, 93 “B+” ranked rock cuts, 618 “B” ranked rock cuts, and 2,800 “C” ranked rock cuts.

For the most hazardous “A” ranked rock cuts, the RHRS includes several detailed categories that are evaluated and scored. These categories include information relating to roadway and slope geometry, geologic parameters, and rockfall history. The numerical score produced for each category are summed together to produce an overall Rockfall Hazard Rating (RHR) score for each “A” ranked rock cut. The higher the number, the more hazardous the rock cut is.

The VTrans RHRS is utilized by the Agency as part of the rock slope management plan to help prioritize hazardous rock cuts for remediation. The future of the RHRS will include incorporation into a Rock Cut Asset Management Program and use in an Arc GIS platform.