QUANDO ANCHE LE FRANE SI DEVONO FERMARE

Il lavoro presenta le problematiche relative al dimensionamento di barriere paramassi a ret

QUANDO ANCHE LE FRANE SI DEVONO FERMARE

Il lavoro presenta le problematiche relative al dimensionamento di barriere paramassi a ret

Dynamic finite element analysis of interceptive devices for falling rocks

The widespread use of net barriers, which are flexible, as opposed to rigid, devices for intercepting falling rocks has led to the need for rigorous design criteria based on safe and sound theoretical methods. Consistently with current practice, full-scale experimental tests are necessary in order to assess the reliability of any such barrier. Here, a new simulation approach based on numerical methods is presented: the analysis of a complete typical falling-rock event has been performed, to study the response of these interceptive devices. A commercial finite element code featuring explicit dynamic capabilities, particularly useful when modelling high-speed phenomena has been used. The simplifying assumptions along with the model geometrical and mechanical data are discussed. Both single net panel and complete barrier simulations are presented. In the latter case, the results are compared with some experimental data obtained from in situ testing. The results of the numerical simulations highlight some limitations in the testing methods which are currently accepted, and suggest the use of new parameters to more precisely characterize the behaviour of such interceptive devices for falling rocks. The benefits of numerical simulations as supplements to or substitutes for full-scale crash tests are emphasized particularly for design or parametric studies

DEM Simulation of the evolution of unstable rock faces: an alternative approach to modelling and back-analysis

The evolution of unstable rock slopes is a process characterised by a succession of discrete events, each one giving rise to a new configuration of the rock face. If these events are put in a wider time frame, they can be seen as a local step contributing to the overall process. The advances in recognition systems, such as laser scanning or georadar techniques, allow to build numerical models of higher and higher precision, where the topographic and geostructural configurations may be precisely reconstructed. These improved capabilities open the possibility for defining highly representative numerical models that can be used for back analysis purposes or the design of risk mitigation works. One possible drawback of such approaches is that they superimpose structural and topographic data, whose compatibility is not independent on the mechanical behaviour of the rock mass. In fact, the initial geometry is depending on the (usually complex) rock slope history, which has a two-fold relationship with the whole set structural and mechanical features of the rock mass. In order to investigate this point, a series of Distinct Element analyses of an unstable rock face located in Bolzano province is performed. The model is characterised by a very simple geometry, and slope evolution is studied by adopting the strength reduction technique. Structural and mechanical information is obtained from an extensive in situ survey. The aim of the simulations is to show how a model based on the available geomechanical information can be used to reproduce the main topographic features of the rock slope, and to perform a back analysis of a selected case history