An experimental comparison of half-scale rockfall protection sandwich structures

International audienceProtection against falling rocks often requires the building of civil engineering structures such as soil reinforced embankments. A recent development consists in building a sandwich cellular structure for this purpose. Cellular structures are efficient technological solutions widely used in civil engineering for various applications. These structures also appear to be well suited to resist rockfall and to act as protective structures against impacts. This paper investigates the behaviour of three sandwich structures based on half-scale experiments. The 1.5 m high cellular sandwich structures were leaned against a concrete wall with the facing made of geocells filled with a coarse granular material. Three different granular materials were used for the kernel part of the sandwich (between the facing and the wall). The experiments were carried out with dead load pendular impacts by a 260 kg spherical boulder with maximal impact energy of 10 kJ. The aim was to evaluate the ability of each kernel material for reducing the stress on the concrete wall

Transmissibilité vibratoire d'un matériau de recyclage

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Comparaison expérimentale semi-vraie grandeur du comportement de trois structures pare-blocs

National audienceOn s'intéresse ici au comportement sous impact de structures sandwichs, alternant des matériaux de granulométries et densités différentes. L'objectif est d'optimiser l'efficacité des ouvrages de protections contre les chutes de blocs rocheux. Les résultats expérimentaux sur trois ouvrages de taille semi-vraie grandeur et soumis à impacts d'énergie croissante sont présentés et discutés. / This paper deals with the mechanical response of sandwich structures, alternating materials differing by both their grain size and densities. The aim is to improve the efficiency of rockfall protection structures. The experimental results obtained on three half-scale structures subjected to increasing energies impacts are presented and discussed

Self-potential signals associated with localized leaks in embankment dams and dikes

International audienceThe self-potential method can be used to detect and monitor anomalous seepages in dams and embankments. In such a case, an electrical field of electrokinetic nature (i.e., associated with pore water flow) can be measured using a set of non-polarizable electrodes typically located at the ground surface or in some wells. This field can be in turn related to the pattern of groundwater flow. We built an experimental dam to investigate to which extent the self-potential method can help characterizing seepages in dams. We first use the finite element method to simulate the ground water flow in a heterogeneous porous and permeable material by solving the groundwater flow equation. The resulting groundwater flow solution is then used to compute the electrical potential distribution by solving the corresponding elliptic partial differential equation. In a preliminary experiment, we could not measure any self-potential anomaly associated with the infiltration of water in the dam. Our numerical simulations showed that the magnitudes of the self-potential anomalies were controlled by (1) the nature of the flow regime (viscous laminar versus inertial laminar flow regimes) and (2) the presence of insulating Polyvinyl Chloride (PVC) tubes located at the end of the preferential flow channels in the structure of the dam. Thanks to these numerical simulations, we added sand at the entrance of the infiltration area in order to reduce the effects of the PVC tubes and to restrain the flow regime to the viscous laminar flow regime. New experiments allowed for detecting a self-potential anomaly with an amplitude of around −9 mV consistent with that obtained through numerical modelling with a finite element simulator. This comparison was used to test the accuracy of the modelling approach and define the strengths and weaknesses of the self-potential method to determine preferential seepages in earth dam structures

Tests de merlons amortisseurs sur une station d'essais d'impacts pendulaires

National audienceSur la station d'impact pendulaire du CER, dans le cadre du projet ANR REMPARe, quatre " structures sandwich " pare-blocs, amortisseurs sont testées. Suivant la nature de leur noyau, elles se déforment, transfèrent l'énergie d'impact et subissent des accélérations de façon différente. Cet article décrit la station, les expérimentations menées et une comparaison comportementale des structures

Soil-embedded optical fiber sensing cable interrogated by Brillouin optical-time domain reflectometry (B-OTDR) and optical frequency-domain reflectometry (OFDR) for embedded cavity detection and sinkhole warning system

A soil-embedded optical fiber sensing cable is evaluated for an embedded cavity detection and sinkhole warning system in railway tunnels. Tests were performed on a decametric structure equipped with an embedded 110 m long fiber optic cable. Both Brillouin optical time-domain reflectometry (B-OTDR) and optical frequency-domain reflectometry (OFDR) sensing techniques were used for cable interrogation, yielding results that were in good qualitative agreement with finite-element calculations. Theoretical and experimental comparison enabled physical interpretation of the influence of ground properties, and the analysis of embedded cavity size and position. A 5 mm embedded cavity located 2 m away from the sensing cable was detected. The commercially available sensing cable remained intact after soil collapse. Specificities of each technique are analyzed in view of the application requirements. For tunnel monitoring, the OFDR technique was determined to be more viable than the B-OTDR due to higher spatial resolution, resulting in better detection and size determination of the embedded cavities. Conclusions of this investigation gave outlines for future field use of distributed strain-sensing methods under railways and more precisely enabled designing a warning system suited to the Ebersviller tunnel specificities