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Flexible facing systems, the main element of which is a pinned net, are widely used to stabilise ground layers on slopes. Today, this technique benefits from decades of successful experience. The optimisation of their design has motivated a great deal of research, based on experiments and numerical modelling, particularly in recent years. This literature review first gives a synthetic overview of the available analytical design methods, before presenting the various research studies that have been carried out on flexible facing systems. The response of flexible facing systems is then discussed in a didactic manner, focusing on the membrane and paying particular attention to the mechanisms and parameters that influence this response. The relevance of current practices in terms of component characterisation tests and analytical approaches to design is then discussed. Finally, the latest research is presented and the best design criteria are discussed.

Flexible barriers are widely used as protection structures against natural hazards in mountainous regions, in particular for containing granular materials such as debris flows, snow avalanches and rock slides. This article presents a discrete element method-based model developed in the aim of investigating the response of flexible barriers in such contexts. It allows for accounting for the peculiar mechanical and geometrical characteristics of both the granular flow and the barrier in a same framework, and with limited assumptions. The model, developed with YADE software, is described in detail, as well as its calibration. In particular, cables are modeled as continuous bodies. Besides, it naturally considers the sliding of rings along supporting cables. The model is then applied for a generic flexible barrier to demonstrate its capacities in accounting for the behavior of different components. A detailed analysis of the forces in the different components showed that energy dissipators (ED) had limited influence on total force applied to the barrier and retaining capacity, but greatly influenced the load transmission within the barrier and the force in anchors. A sensitivity analysis showed that the barrier’s response significantly changes according to the choice of ED activation force and incoming flow conditions.

This study addresses the key issue of the interaction between debris flows and flexible barriers based on small-scale experiments for which both the flowing mixture and the barrier were designed to achieve similitude with real situations in Alpine environments. The considered debris consisted of a large solid fraction mixture with large and angular particles, flowing down a moderately inclined flume and resulting in near-critical flows, with a Froude number in the 0.9–2 range. The flexible barrier model consisted in 3D printed cables and net. The flow characteristics, evolution and deposition after contact with the barrier as well as the deformation and the loading experienced by the barrier were addressed varying the flume inclination and released mass. Four different interaction modes between the flow and the barrier are identified increasing the flow kinematics. A model based on the hydrostatic pressure assumption reveals relevant for estimating the total force exerted on the barrier when all the released material is trapped. This force doubles in case there is barrier overflow.

Open check dams are strategic structures to control sediment and large-wood transport during extreme flood events in steep streams and piedmont rivers. Large wood (LW) tends to accumulate at such structures, obstruct their openings and increase energy head losses, thus increasing flow levels. The extent and variability to which the stage–discharge relationship of a check dam is modified by LW presence has so far not been clear. In addition, sufficiently high flows may trigger a sudden release of the trapped LW with eventual dramatic consequences downstream. This paper provides experimental quantification of LW-related energy head loss and simple ways to compute the related increase in water depth at dams of various shapes: trapezoidal, slit, slot and sabo (i.e. made of piles), with consideration of the flow capacity through their open bodies and atop their spillways. In addition, it was observed that LW is often released over the structure when the overflowing depth, i.e. total depth minus spillway elevation, is about 3–5 times the mean log diameter. Two regimes of LW accumulations were observed. Dams with low permeability generate low velocity upstream, and LW then accumulates as floating carpets, i.e. as a single floating layer. Conversely, dams with high permeability maintain high velocities immediately upstream of the dams and LW tends to accumulate in dense complex 3D patterns. This is because the drag forces are stronger than the buoyancy, allowing the logs to be sucked below the flow surface. In such cases, LW releases occur for higher overflowing depth and the LW-related head losses are higher. A new dimensionless number, namely the buoyancy-to-drag-force ratio, can be used to compute whether (or not) flows stay in the floating-carpet domain where buoyancy prevails over drag force.

This article proposes a procedure for developing tools to quantify the on-site efficiency of any rockfall barrier. This procedure relies on meta-modeling techniques to predict the barrier ability in arresting rock blocks, whatever their trajectory. For demonstration purpose, a specific low-energy barrier for which a finite element model was available is considered. The barrier response is simulated varying six parameters describing the rock block kinematics. Six different methods are used to create meta-models predicting the simulated barrier response. The ability of each method in creating meta-models with good prediction capacities is evaluated. Meta-models created utilizing the best methods are then used to quantify the efficiency of the barrier in arresting rock blocks in two real situations. These situations exhibit very similar 95% percentiles of the block passing height and kinetic energy but very different distributions for the other parameters describing the kinematics of the rock blocks. The predictions reveal that the barrier efficiency is extremely site-dependant. The discussion addresses the meta-models performance and highlights the benefits in using such meta-models for quantifying the barrier efficiency, in particular with respect to more classical barrier design approaches. Last, the proposed eight-step procedure for generating meta-models to be used in operational contexts is described.

This study deals with an innovative type of protection structure for gravity-driven natural hazards such as landslides (slope failures, rockfalls, etc.) consisting of a vertical wall made up of interconnected concrete blocks. This type of articulated structure presents many advantages including reduced footprint, versatility and easy maintenance. The response of such a structure under impact is investigated considering projectiles with kinetic energies of 520 and 1020 kJ, based on real-scale impact experiments and numerical simulations. The finite difference model is described in detail as well as the experiments. The model was developed focusing on the global structural impact response while keeping the computation time reasonable. The model parameter calibration is based on data in the literature and complemented with specific measurements. The experimental data allows us to describe the impact response of the structure and identify the main mechanisms controlling this response (sliding, tilting, and fracturing). The simulation results revealed that the model is efficient in mimicking this response, in terms of deformation amplitude and evolution with time. Finally, the numerical model made it possible to highlight complex mechanisms that were not possible to experimentally determine such as the different energy dissipation modes within the wall.HighlightsFull-scale impact experiments demonstrating the impact strength of articulated walls made of concrete blocks and metallic elements up to 1000 kJ.Finite difference model of the structure validated against experimental data.Highlights of the prevailing mechanisms involved in the impact response of the structures based on both numerical and experimental investigations.Based on simulation results, friction between concrete blocks and damage to concrete contribute up to 70% of the projectile kinetic energy.

Rockfall propagation models are routinely used for the quantitative assessment of rockfall hazard. Their capacities and limitations remain difficult to assess due to the limited amount of exhaustive experimental data at the slope scale. This article presents experiments of block propagation performed in a quarry located in Authume (France). This study site was chosen for its complexity, related with the presence of topographical discontinuities and of configurations promoting block rolling. A total of more than one hundred blocks were released on two propagation paths. The propagation of the blocks was assessed by measuring the block stopping points as well as their kinematics at specific locations of the paths, called evaluation screens. Significant variability of the stopping points and of the block kinematics at the evaluation screens was observed, and preferential transit and deposit zones were highlighted. The analysis of the results showed predominant effect of topography, in particular that related to topographical discontinuities. Significant influence of local and small scale parameters (e.g., block orientation, local topography) was also highlighted. These conclusions are of particular interest for researchers or practitioners who would like to assess the relevance of propagation modeling tools considering this complex study site. In this configuration, the quality of block propagation simulations should notably rely on the accuracy of digital terrain models, and on the integration of local conditions effects using physically based approaches.

This study is based on the analysis of the residual rockfall hazard at the elements at risk and accounts for the variability of the rock release parameters influencing the trajectory. The design of protection structures is conducted in two phases: a functional design phase consisting of quantifying the structure height from the rock passing height distribution and a structural design phase where the structure required capacity is assessed from the rock passing energy distribution. This framework is used on a well-documented study site for identifying the effects of the definition of the rocks release conditions, limited to the rock volume and falling height, on the design and efficiency of protection fences. The rock volume is modeled using a random variable, with different probabilistic laws. A probabilistic method is also used to analyze the effect of the rock volume distribution. These sensitivity analyses are conducted using a point estimate method for saving computation time. In this work, the initial falling height is shown to have a negligible influence on both the functional and structural designs of the fence. On the contrary, the rock volume range appears to be the leading parameter. The influence of the distribution law is shown to be of second order. The proposed approach may be extrapolated to other uncertain or variable parameters, as well as to other types of passive rockfall protective structures.

This paper presents a numerical model based on Discrete Element Method used to reproduce a series of tests of dry granular flow impacting a rigid wall. The flow was composed of poly-dispersed non-spherical particles flowing in an inclined chute with different inclination angles. The model has been calibrated based on the flow thickness measurements and the shape of the flowing particles (a single sphere and a clump). Quantitative comparison with experimental data showed good agreement in terms of peak impact force on the wall, the time of the peak and also the residual force values at the end of the tests. After validating the model, relation between microstructure and the normal impact force against the wall was investigated, by comparing the variation of impact force values along the height of the wall for different tests. Microstructural heterogeneities were observed in the impacting and depositing stages of the flow, indicating the presence of arching effect in the granular medium behind the wall.

Flexible rockfall barriers are protection structures used to mitigate rockfall hazards in mountainous areas. The complex nonlinear mechanical behavior of these structures under impacts requires powerful modeling tools to perform structural analysis. In this article, a generic computational approach to rockfall barriers analysis is introduced. First, the generic formulation and numerical implementation in the GENEROCK software are detailed. Then, two barrier models are considered and validated against experimental full-scale tests on two different technologies. This numerical investigation permits insightful numerical investigation of the barriers’ behavior. Exploratory numerical simulations are eventually performed to highlight the strengths and generality of the proposed approach. The influence of the curtain effect modeling in simulation results is presented. The effects of repeated impacts on rockfall barriers are investigated and present new insight into barrier behavior and management practices. Stochastic modeling methods are also used to study the propagation of uncertainty and variability of the structure itself in its dynamic response.