Analisi numerica del comportamento di barriere paramassi

Mountainous areas are prone to natural hazards like rockfalls. Among the many countermeasures, rockfall protection barriers represent an effective solution to mitigate the risk. They are metallic structures designed to intercept rocks falling from unstable slopes, thus dissipating the energy deriving from the impact. This study aims at providing a better understanding of the response of several rockfall barrier types, through the development of rather sophisticated three-dimensional numerical finite elements models which take into account for the highly dynamic and non-linear conditions of such events. The models are built considering the actual geometrical and mechanical properties of real systems. Particular attention is given to the connecting details between the structural components and to their interactions. The importance of the work lies in being able to support a wide experimental activity with appropriate numerical modelling. The data of several full-scale tests carried out on barrier prototypes, as well as on their structural components, are combined with results of numerical simulations. Though the models are designed with relatively simple solutions in order to obtain a low computational cost of the simulations, they are able to reproduce with great accuracy the test results, thus validating the reliability of the numerical strategy proposed for the design of these structures. The developed models have shown to be readily applied to predict the barrier performance under different possible scenarios, by varying the initial configuration of the structures and/or of the impact conditions. Furthermore, the numerical models enable to optimize the design of these structures and to evaluate the benefit of possible solutions. Finally it is shown they can be also used as a valuable supporting tool for the operators within a rockfall risk assessment procedure, to gain crucial understanding of the performance of existing barriers in working conditions

A New Technique for Deep in situ Measurements of the Soil Water Retention Behaviour

In situ measurements of soil suction and water content in deep soil layers still represent an experimental challenge. Mostly developed within agriculture-related disciplines, field techniques for the identification of soil retention behaviour have been so far employed in the geotechnical context to monitor shallow landslides and seasonal volume changes beneath shallow foundations, within the most superficial ground strata. In this paper, a novel installation technique is presented, discussed and assessed, which allows extension of the use of commercially available low-cost and low-maintenance instruments to characterise deep soil layers. Multi-depth installations have been successfully carried out using two different sensor types to measure the soil suction and water content up to 7\u2009m from the soil surface. Preliminary laboratory investigations were also shown to provide a reasonable benchmark to the field data. The results of this study offer a convenient starting point to accommodate important geotechnical works such as river and road embankments in the traditional monitoring of unsaturated soil variables

A simple continuum approach to predict the drained pull-out response of piles for offshore wind turbines

The article presents a continuum approach to predict the response of pile foundations for jacket-supported offshore wind turbines. Tensile loading conditions are examined, which may be critical for piles used in combination with this structure type, generally adopted to exploit wind energy in intermediate water depths. The approach is developed to guarantee a simple implementation with a limited number of input data easily attainable from cone penetration tests and laboratory tests, and to ensure computational cost-effectiveness. Data from technical-scale tests on open-ended steel piles driven in dense sand and subjected to drained pull-out are used to assess the performance of the approach. The results are shown to be accurate, approximating rather closely the experimental load–displacement curves. The accuracy of the approach is also compared to that obtained with a recently proposed design method, to investigate the predictive capacity of the approach and its potential to support preliminary design activities

A Meta-Model-Based Procedure for Quantifying the On-Site Efficiency of Rockfall Barriers

International audienceThis 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

Metamodelling of the load-displacement response of offshore piles in sand

International audienceThe paper illustrates the development of metamodels of the response of steel piles driven in sand and subjected to pull-out. The metamodels are created for the prediction of the pile tensile capacity and secant stiffness. They were developed using the results of finite element analyses, which made use of finite element models of robustness assessed employing a selection of available data from large-scale model pile tests. Four hundred finite element analyses allowed for the calibration of very accurate metamodels, which were also demonstrated to closely track the outputs of the experimental results. Once calibrated, the metamodels can be used independently from the finite element models they stemmed from. The outcomes of the study show that metamodels of piles response can yield very accurate results within a wide and realistic range of soil-pile configuration, avoiding the laborious implementation and computational cost which underpins the use of finite element models. As the use of metamodels in this context is new, the paper relies on particularly simplified problem, but the procedure could be extended to accommodate modelling features of higher complexity

Investigating the effectiveness of semi-rigid protection fence

Semi-rigid, low energy rockfall protection fences, can provide in certain circumstances a convenient alternative to flexible falling rock protection barriers, if their installation is planned in an adequate and comprehensive manner. The response of these structures has been recently investigated (de Miranda et al., 2015; Mentani et al. 2016). Results of these studies have shown a dependency of the structure capacity on impact conditions. Realistic impact conditions can be applied to barrier models once they are suitably incorporated in an advanced rockfall simulation tool (Bourrier et al. 2014). Result of the simulations can then provide an effective support to intervention plans. The implementation of barrier models in a rockfall simulation model is a complex task and should rely on a thorough understanding of the fence structural behaviour. In this short note, the numerical response of a simple semi-rigid protection barrier is explored to the scop

Metamodeling to emulate plate anchor response in spatially variable soil

This paper describes a metamodelling approach to investigate the behaviour of a plate anchor in spatially variable soil. The approach explores the effect of variability in undrained shear strength on the monotonic holding capacity. The problem is firstly analysed through a selected number of two-dimensional finite element (FE) analyses. As this is computationally expensive, relatively few analyses are performed, with the metamodel developed to map the response over a wider range of parameters. This uses mathematical operators calibrated to emulate the FE models, which can be built on a relatively small data set, with the overall objective to retain the accuracy of the original FE model at negligible computational cost. In future, this approach may support design by considering uncertainties that are common for any offshore foundation problem, providing a tool that can be easily coupled with traditional probabilistic design approaches

Modelling for the design of passive protection measures against rock fall

An increasing need of protecting the civil installations against natural hazards—like very rapid soil and rock movements—is due to the extensive mountain territories usage for infrastructures and residential areas. In this study, the so-called flexible falling rock protection barriers, which can be numbered among passive solutions against rock fall, are analyzed in detail. These structures have been historically designed on the basis of full-scale impact tests on barrier prototypes. Based on a reliable experimental database, a numerical approach has been recently proposed for the modelling of these struc-tures, which has proved to reproduce all the relevant quantities for the description of the barrier response with time. The very good fit of the experimental and numerical results can provide further confidence on the use of such models as predictive tools to support the design of flexible falling rock protection barriers under different scenarios

A PROBABILISTIC APPROACH TO INTEGRATE THE EFFECT OF PROTECTION SYSTEMS INTO ROCKFALL HAZARD ASSESSMENT

International audienceThe paper introduces the essential features of a new strategy to develop reliable and computa-tionally cost-effective models of the mechanical response of a rockfall barrier subjected to realistic impact conditions. The approach combines the use of three-dimensional, non-linear and dynamic finite element models of a rockfall barrier with a reliability-based probabilistic approach. The strategy may apply to any type of rockfall barrier in presence of any condition of impact and it is devised so it can be implemented in rockfall propagation simulation tools. Applications of the approach are wide and includes the evaluation of the residual hazard down existing protection works and the reliable planning of new interventions