| This paper contains a method for the analysis of rockfall risk along roads and motorways.
The method is derived from the Rockfall Hazard Rating System (RHRS) developed by
Pierson et al. (1990) at the Oregon State Highway Division. The RHRS provides a rational
way to make informed decisions on where and how to spend construction funds. Exponential
scoring functions are used to represent the increases, respectively, in hazard and in
vulnerability that are reflected in the nine categories forming the classification. The
resulting total score contains the essential elements regarding the evaluation of the
degree of the exposition to the risk along roads.
In the modified method, the ratings for the categories "ditch effectiveness",
"geologic characteristic", "volume of rockfall/block size", "climate and water
circulation" and "rockfall history" have been rendered more easy and objective.
The main modifications regard the introduction of Slope Mass Rating by Romana (1985,
1988, 1991) improving the estimate of the geologic characteristics, of the volume
of the potentially unstable blocks and the underground water circulation. Other
modifications regard the scoring for the categories "decision sight distance"
and "road geometry". For these categories, the Italian National Council's standards
(Consiglio Nazionale delle Ricerche - CNR) have been used (CNR, 1980). The method
must be applied in both the traffic directions because the percentage of reduction
in the decision sight distance greatly affects the results.
An application of the modified method to a 2km long section of the Sorrentine road
(no 145) in Southern Italy was developed. A high traffic intensity affects
the entire section of the road and rockfalls periodically cause casualties, as well
as a large amount of damage and traffic interruptions. The method was applied to
seven cross sections of slopes adjacent to the Sorrentine road. For these slopes,
the analysis shows that the risk is unacceptable and it should be reduced using
urgent remedial works. |