NYDOT: ROCK SLOPE RATING PROCEDURE

[tuanpecc1]

ROCK SLOPE RATING PROCEDURE

Publisher: NEW YORK STATE DEPARTMENT OF TRANSPORTATION
Pages: 48
Date: APRIL 2007

INTRODUCTION
In the winter of 1988, NYSDOT resident maintenance engineers were asked to send the Geotechnical Engineering Bureau lists of rock slope locations in their areas of responsibility that might conceivably be considered potential rockfall problem sites, screening them by the following criteria (listed it, order of importance.) :
1 . Areas with rockfall histories,
2. Posted rockfall zones,
3 . Obviously unstable rock masses,
4. Overhanging rocks,
5. Highly fractured and jointed oversteepened slopes (those higher than the setback from
the shoulder edge),
6. Areas of ice buildup on slopes,
7. Fallen rock in ditches,
8. New cracks or gaps in the rock,
9. Areas with soil deltas at the toes of rock slopes, and
10. Rock- slabs on slopes inclined toward the roadway.
A total of 1741 sites were identified and then evaluated by geologists from the Geotechnical Engineering Bureau, using an initial rating system based on a procedure originally developed for the Federal Highway Administration (FHAN'A) by Duncan C. Wyllie of the. geotechnical consulting firm of Golder Associates. This procedure was considered state-of-the art at the time, and was included in FHWA's Rock Slopes manual . Although the Department used this system in developing a rock slope ranking, no implementation policy was established. Also, identification of potential rockfall sites is an open-ended process, because sites may be added at any time. NZ'SDOT has now devised a revised system believed to have these three distinct advantages:
It isolates three components of a possible rockfall-vehicle accident as independent factors,
It more objectively addresses the cluestion of how much risk is associated with a falling rock flitting a vehicle, as well as the risk of a vehicle hitting a fallen rock, and
It considers not only risk posed by an existing rock slope, but level of risk remaining after reinediation .
The proposed rating procedure for rock slopes was presented to the Assistant Commissioner and Chief Engineer, approved, and a working draft issued in May 1993.

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