The effectiveness of protection systems toward rockfall risk mitigation

Hazard

The transcription factor BCL11A defines distinct subsets of midbrain dopaminergic neurons.

Midbrain dopaminergic (mDA) neurons are diverse in their projection targets, effect on behavior, and susceptibility to neurodegeneration. Little is known about the molecular mechanisms establishing this diversity during development. We show that the transcription factor BCL11A is expressed in a subset of mDA neurons in the developing and adult murine brain and in a subpopulation of pluripotent-stem-cell-derived human mDA neurons. By combining intersectional labeling and viral-mediated tracing, we demonstrate that Bcl11a-expressing mDA neurons form a highly specific subcircuit within the murine dopaminergic system. In the substantia nigra, the Bcl11a-expressing mDA subset is particularly vulnerable to neurodegeneration upon α-synuclein overexpression or oxidative stress. Inactivation of Bcl11a in murine mDA neurons increases this susceptibility further, alters the distribution of mDA neurons, and results in deficits in skilled motor behavior. In summary, BCL11A defines mDA subpopulations with highly distinctive characteristics and is required for establishing and maintaining their normal physiology

An Equivalent Continuum Approach to Efficiently Model the Response of Steel Wire Meshes to Rockfall Impacts

Steel wire meshes are a key component of rockfall protection barriers. The efficiency in reproducing the structure response with numerical methods relies upon the specific modelling technique employed to capture the wire mesh behaviour. The fabric of some rockfall meshes, such as chain-links is quite complex, which leads to sophisticated and costly numerical models, if modelled accurately. This paper presents an efficient approach to model the response of steel wire meshes to rockfall impacts by using shell elements to develop an equivalent continuum model. An elastoplastic behaviour is prescribed to the shell elements to reproduce the results of a set of experimental data, carried out on mesh portions under various load paths and boundary conditions. The idea is that simple laboratory tests can be used to calibrate an effective numerical model of the steel wire mesh with a significantly lower computational cost if compared to other effective solutions. The model\u2019s ability in yielding consistent results when implemented at the structure scale is then assessed, based on the data of full-scale impact tests on a three-span low-energy rockfall barrier. The method can be extended to other wire mesh types and can find convenient application on exploring the response of a rockfall barrier with a cost-effective tool

Calibration of an equivalent shell model for a chain-link mesh

In recent years, there has been an up surging interest toward the investigation of the response of low energy rockfall barriers. The mechanical response of these structures largely depends on the interception structure. In this short note, the response of a chain-link mesh, typically used for this barrier type, is explored, by means of dynamic and static tests on panel portions at different scale. Based on the experimental data, an approach to develop an accurate and com-putationally effective FE model of the net is then described

Design of falling rock protection barriers using numerical models

A numerical approach has been recently devised by the authors for the modelling of falling rock protection barriers, metallic structures used as passive measures against rockfall. Following this approach, in this study a FE model of a specific barrier type is developed. The constitutive parameters of the model are calibrated employing the data of a series of experiments carried out onto the main barrier components such as the interception structure and the energy dissipating devices. Then, the ability of the FE model to reproduce the real barrier behaviour is explored by simulating, retrospectively, a set of experiments carried out onto real-scale prototypes of the barrier, under various impact conditions. The very good fit of the rather complex experimental and numerical results can assess the ability of the FE model to reproduce the prototype behaviour, so validating the reliability of the adopted numerical approach and giving further confidence to the use of such models as design tools. Therefore, based on the numerical results, the considered barrier model has been enhanced in terms of cost-effectiveness and on-site performance

Dynamic analysis of flexible falling rock protection barriers

A numerical approach has been recently devised for the modelling of falling rock protection barriers, metallic structures used as passive measures against rockfall. The paper assesses the reliability of the approach and explores its potential as a predictive tool, with reference to a specific barrier type

The effectiveness of protection systems toward rockfall risk mitigation

A comprehensive method for rockfall risk analysis has been recently proposed by the Autonomous Province of Bolzano within the context of European project PARAmount (imProved Accessibility, Reliability and safety of Alpine transport infrastructure related to MOUNTainous hazard in a changing climate). The procedure is especially aimed to a proper planning of effective countermeasures through a rational management of the existent. To such purpose, the process of hazard evaluation has been especially designed to accommodate the presence of protection systems located in the area interested by the analysis. The application of the procedure requires a thorough knowledge of the considered works, which includes passive and active protection systems. With reference to the passive measures, the paper presents a numerical study of falling rock protection barriers at present installed within the Province territory. The investigation addresses the actual effectiveness of these structures toward hazard mitigation. Preliminary analyses and results, concerning a carefully carried out selection of barrier types occurring on the territory are described and commented

Numerical modelling of a low-energy rockfall barrier: New insight into the bullet effect

This paper investigates the dynamic respons eof low energy, semi-rigid rockfall barriers. The study is based on a FE model that reproduces the geometry, components and connections of the existing systems that were previously tested at The University of Newcastle. The mechanical behaviour of the relevant barrier components was calibrated from simple mechanical tests and the response of the assembled system, i.e. 2 m high, 15 m long rockfall barrier, was validated against of full-scale tests results. Following a satisfactory validation of the model, further dynamic non-linear analyses were conducted to investigate the dependence of the full system performance to the size of impacting blocks. Interestingly, the total failure energy was found to evolve non-monotonically with block size because of dynamic effects that seem to prevailfor impact speeds in the range of 15-20 m/s. The study also highlights the complex effects of adding intermediate longitudinal cables to the system. An improvement of the barrier performance is observed for the large blocks but the bullet effect is exacerbated for small blocks