Abstract
Net fences are among the most widespread passive protective measures to mitigate the risk from rockfall events. Despite the current design approach being based on partial safety factors, a more efficient time-dependent reliability approach has been recently introduced by the authors. This method is influenced by various parameters related to the geometry and the kinematics of the block, i.e., the uncertainty related to the distribution of the size of the impacting block, its occurrence probability, and the shape of the right-tail of the distributions of its velocity and trajectory height at the location of the net fence. Furthermore, the block size distribution of the deposit greatly affects the results. The present work focuses on the possible range of such parameters to encompass the great majority of real events. The obtained results are compared with the current design approaches based on fixed partial safety factors. It emerges that the choice of the characteristic mass of the block and the failure probability greatly influence the results. Moreover, if a set of partial safety factors is assigned to different sites, an intrinsic variability in the failure probability has to be accepted. Suggestions for an accurate procedure and future developments are provided.
Highlights
Rockfalls are among the most hazardous landslide phenomena, due to their abrupt occurrence and the very high involved energies [1,2,3,4]
The values of the equivalent partial safety factors are affected by the ratios v99 /v95 and h99 /h95, which are related to the slope and rockfall propagation, the parameter α, which is related to the impacting block mass distribution, and the coefficient of variation of the mass COVm, which directly depends on the number of surveyed blocks
A novel time-dependent reliability approach was introduced for the design of rockfall net fences [36]
Summary
Rockfalls are among the most hazardous landslide phenomena, due to their abrupt occurrence and the very high involved energies [1,2,3,4]. From the results of the rockfall propagation analyses, an appropriate commercial product is selected [17] among the ones whose energy absorption capacity and the nominal height, evaluated with standard procedure [19], are greater than the correspondent impact energy and passing height of the simulated blocks This approach considers two possible failure modes: the falling block trajectory is higher than barrier height, or because its energy is larger than the barrier capacity. With the aim of providing a compelling solution for the designer, De Biagi et al [36] implemented their approach into the current practice [30]: equivalent partial safety factors for the impacting block energy, mass, velocity, and height were derived, and properties and the affecting variables were analysed.
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