Reliability analysis and partial safety factors approach for rockfall protection structures

The design of rockfall protection structures must consider several variables, such as the energy and the height of the impacting block. Nevertheless, the statistical distributions of these variables do not follow a predefined law. Reliability analyses aim at finding how the random nature of the parameters describing a structure affects its performance and safety. In the geotechnical framework, generally, the limit states approach is adopted, accounting for the design values of both effects of actions and resistances. The present paper proposes a solution to a time-variant reliability problem to define the design values of the parameters for net fences design, i.e. velocity, mass and trajectory height of the impacting block, accounting for the spreading of their distributions and rockfall occurrence process. The proposed approach is incorporated into the semi-probabilistic design framework and the equivalent partial safety factors of the main variables and the corresponding characteristic values are discussed. The results highlights that the values of the partial safety factors are affected by the ratios between two relevant values of the right-tail of the distributions of height and velocity, i.e. the 99th and the 95th percentiles, and by the parameters of the statistical distribution of the blocks found at the foot of the cliff.