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Many geotechnical problems involve pavements in Algerian arid regions; the main among them being related to the scarcity of standard materials. Recently, numerous studies were carried out on the va...

The ecological and environmental issues today encourage the use of eco-geo-materials that consume less «grey energy» , such as raw earth building material. This raw earth material is inexpensive and is generally available on the construction site. The compressive strength and ductility have a major role on its mechanical behavior. However, few studies are effectively dedicated to estimate both the compressive strength and the ductility property of raw earth materials. Treated with a very low percentage of binders, the raw earth is transformed into an eco-material suitable for use in the construction. However, the experimental study of the raw earth concrete mechanical properties presents uncertainties related to the bio-sourced nature of its components, such as plant fibers and raw earth. In this study, the raw earth samples of 25 different formulations were casted and tested for 90 days of curing time. The samples were tested for unconfined compressive strength through which ductility index were inferred. In order to optimize the formulation of this raw earth material, a «Design of Experiments» was conducted to study the effect of the various components on these two mechanical properties. A multivariate statistical regression technique of PLS, Partial Least Square, was performed to evaluate the design. This PLS technique was selected because of the complicated experimental design data along with different constraints on model based on the two responses. The obtained results show this technique could be a helpful tool to improve and optimize a raw earth concrete formulation.

Extreme waves play a crucial role in marine inundation hazards and coastal erosion. Prediction of non-linear wave–wave interactions is crucial in assessing the propagation of shallow water extreme waves in coastal regions. In this article, we experimentally study non-linear wave–wave interactions of large-amplitude focused wave groups propagating in a two-dimensional wave flume over a mild slope (β=1:25). The influence of the frequency spectrum and the steepness on the non-linear interactions of focused waves are examined. The generated wave trains correspond to Pierson–Moskowitz and JONSWAP (γ=3.3 or γ=7) spectra. Subsequently, we experimentally approach this problem by the use of a bispectral analysis applied on short time series, via the wavelet-based bicoherence parameter, which identifies and quantifies the phase coupling resulting from non-resonant or bound triad interactions with the peak frequency. The bispectral analysis shows that the phase coupling increases gradually and approaches 1 just prior to breaking, accordingly with the spectrum broadening and the energy increase in high-frequency components. Downstream breaking, the values of phase coupling between the peak frequency and its higher harmonics decrease drastically, and the bicoherence spectrum becomes less structured.

Building construction technology by raw earth materials is already known and used since ancient times. The raw earth material is abundant, low cost, requires very low energy to manufacture and does not generate waste. Ductility is required for earth building materials in the areas of seismic risks where the earth buildings are particularly vulnerable to earthquakes. Hence, a raw earth treatment by binders and vegetal fibers is one of the techniques applied to improve its strength and ductility. This paper presents the use of mixture design as a tool to evaluate and analyze the plastic behavior of the raw earth material. The ductility is quantified through two ductility indices. The results indicate that an alternative ductility index based on the post-peak behavior of the material could be used to define a ductility criterion to meet specific requirements of the seismic regions.

International audience; The propagation of solitary waves above an horizontal bottom and a sloping bottom is considered in this paper. Experiments are carried out in a wave flume above smooth beds. The solitary waves are generated with a piston-type wave maker, using an impulsive mechanism (Marin, F et al. (2005)). Close to the generation zone, the profile contains elevation and depression components. These depressions are attached to the main solitary wave during the propagation along the flume. The energy damping along the horizontal and sloping bottoms (Zhang, C et al. (2010)), the wave height variation in the shoaling zone, the breaking modes and the runup height are investigated. It is shown that spatiotemporal diagrams are adapted for tracking the evolution of solitary waves propagating from a horizontal bed to a sloping bed (Chang, L et al. (2014)). The breaking parameters are obtained using high resolution cameras. Present results are in good agreement with earlier studies (Hsiao, S et al 2008). A new formula is proposed for the estimation of runup height. Figure 1. Sketch of the experimental setup A 0 = Amplitude of solitary wave 3 meter form the wave maker, m. A 1 , A 2 = Wave heights for water depths h 1 and h 2 , m. A b = Breaking height, m. A s = Solitary wave amplitude, m A t = Amplitude of solitary wave at the toe of the beach, m. C gr = = Group velocity corresponding to the main solitary wave, m.s-1 E = Energy on a unit length in the direction transversal in the direction of wave propagation, J.m-1 g = Acceleration of gravity, m.s-2 h 0 = Stillwater depth, m h b = Breaking depth, m. L 0 = Wave length scale, m. R = Runup height, m. S 0 = Slope parameter. T = Duration of impulse, s β = 0.04= Slope, rad. ε=A 0 /h 0 = Non linearity parameter (1). ε'=A t /h 0 = Non linearity parameter (2). ɳ = free surface elevation, m = mean water level, m ρ = Water density, 1g.cm-3

The propagation of focused wave groups in intermediate water depth and the shoaling zone is experimentally and numerically considered in this paper. The experiments are carried out in a two-dimensional wave flume and wave trains derived from Pierson-Moskowitz and JONSWAP spectrum are generated. The peak frequency does not change during the wave train propagation for Pierson-Moskowitz waves; however, a downshift of this peak is observed for JONSWAP waves. An energy partitioning is performed in order to track the spatial evolution of energy. Four energy regions are defined for each spectrum type. A nonlinear energy transfer between different spectral regions as the wave train propagates is demonstrated and quantified. Numerical simulations are conducted using a modified Boussinesq model for long waves in shallow waters of varying depth. Experimental results are in satisfactory agreement with numerical predictions, especially in the case of wave trains derived from JONSWAP spectrum., Comment: 36 pages, 13 figures, 1 table, 38 references. Other author's papers can be downloaded at http://www.denys-dutykh.com/

National audience; Notre travail repose sur une étude expérimentale de la propagation des trains d’ondes fortement non-linéaires se propageant en eau intermédiaire vers la zone côtière. Trois méthodes de génération ont été employées. Ces méthodes dépendent du spectre à partir duquel les trains d’ondes sont construits. Il s’agit du spectre gaussien, spectre de PiersonMoskowitz et spectre de JONSWAP. Les essais ont été réalisés dans le canal à houle du laboratoire M2C (UMR 6143 Caen). Les signaux obtenus par les sondes résistives sont utilisés pour la détermination de l’évolution spatiale des transferts énergétiques et des interactions non-linéaires entre les composantes fréquentielles. Un partitionnement spectral a été effectué sur chaque spectre de référence pour quantifier les variations spatiales de l’énergie dans chaque gamme de fréquences. Des transferts énergétiques en amont et en aval de déferlement ont été mis en évidence et ensuite quantifiés. Une approche bispectrale par ondelettes a été utilisée dans le but de quantifier les interactions non-linéaires entre les composantes fréquentielles grâce à un paramètre appelé bicohérence. Au cours de la propagation, ce paramètre augmente progressivement et atteint des valeurs proches de 1 au moment du déferlement et décroit drastiquement en aval de ce déferlement.

Experiments are carried out in a flume without slope. Tests are performed for different unidirectional steady flow conditions, varying the initial sediment thickness and recirculating the sediment to ensure a constant supply condition, from an extremely limited sediment supply to an unlimited sediment supply condition. The formation of ripples and dunes is considered from an initially flat bed. The growth rate of the mean wavelength of ripples depends on the sediment supply, whether it is extremely limited or not. In spite of a rapid initial growth when sediment supply is extremely limited, the growth rate is much higher when sediment availability increases. As far as the equilibrium dimensions of the sedimentary structures are concerned, an increase of mean heights of ripples and dunes is pointed out when the sediment availability increases. The similar trend is found for mean ripple lengths but no clear trend is exhibited for dunes which are few and irregular. The empirical law proposed by Tuijnder et al. (2009) in a fluvial context for relative dune heights in the case of sediment limited supply conditions can be used for dunes in a coastal context. However, this formulation cannot be extended to ripple heights for which a dependence with flow conditions is noted. Ripple equilibrium lengths can be described with a relation suggested by Tuijnder et al. (2009) for dunes if an adaptation factor is considered.

(IF N/A; Q4); International audience; Laboratory-scale waves of two distinct types were generated in a two- dimensional wave flume to model the spatial evolution of the frequency spectrum in the nearshore zone. The two generated types are Gaussian wave groups of different spectra widths and solitary waves. In the experiment, the time series of free surface elevation along the flume are obtained along a distance of 10m using wave gauges. For each Gaussian wave train, four regions were defined, namely peak, transfer, high frequency and low frequency region referred to as E1, E2, E3 and E4. The repartition was based on the maximum frequency spectrum situated in E1 at X = 4m. Focusing is a complex process; this is mainly due to nonlinear energy transfer between different frequency ranges. It was concluded that the energy keeps stable in E1 and spreads toward E3 before breaking. The frequency spectrum in E2 has a decreasing trend during the wave train propagation. After the breaking, the frequency spectrum in E2 stops decreasing. It was found also that frequency spectrum increases during the focusing process in E4. Concerning solitary waves, it was found that the frequency spectrum of the main solitary wave decreases as the wave approaches the breaking zone.

International audience; This paper describes an experimental investigation of runup for intermediate sandy beaches from a physical modelling in a wave flume with tide simulation. Shoreline elevation measurements are acquired over a wide range of conditions using an optical method. Simultaneous morphological and hydrodynamic changes are considered to determine the best parameters to predict the maximum wave runup. The tidal level significantly affects the breaking conditions (position, height and type), and the slopes of the beach. Present data show that the surf zone slope and the wave breaking height should be used to estimate the maximum runup. The results are compared with previous formulations issued from the literature. A new formula is proposed for the runup estimation for intermediate beaches.

International audience; Sudden waves of considerable height are frequently observed at sea. These waves, with abnormally high amplitude, do not occur only in deep Ocean, but also in the coastal zone. A lot of studies have considered these waves in the open ocean; however, they have received little attention in the coastal zone. The physical processes involved in the transformation of these waves from the open sea to the coastal zone are poorly understood, despite the significant impact these waves may have on the coasts, such as overtopping, material damages, and erosion. The aim of the present work is to bring a contribution to the study of these processes from physical modeling. Present tests are carried out in a 22 m long, 0.8 m wide, and 0.8 m high wave flume. Solitary waves are generated. Preliminary tests have been performed to compare the characteristics of the experimental waves with the theoretical prediction of Boussinesq [1]. A good agreement is obtained as well for the wave form, than for the wave speed and duration. The transformation of solitary waves during their propagation towards the shore has been studied using an artificial 4% slope in the flume, placed 9.5m downwards from the wave paddle. A particular attention has been focused on the evolution of the wave energy. Above the 9.5m long horizontal bed upwards from the slope, an energy dissipation ranging from 20 % to 30 % has been obtained. However, the wave energy was found to increase during the propagation of the solitary waves above the sloping bottom, from 15 % to 30 % according to the considered tests, in agreement with the results depicted in [2]. Sapce-time diagrams have been plotted, allowing to describe the propagation of solitary waves above the horizontal and sloping bed. On these diagrams we can clearly see that the solitary wave has a symmetric profile about its crest and an approximately constant celerity before it reaches the slope. The wave height then increases when the solitary wave climbs up the slope. As water depth decreases, the solitary wave progresses with increasing of asymmetry and the front became more and more steep. Finally, the maximum runup is considered, and a new formula is proposed for its estimation (depending on the tangent of the 4% slope) Formation of freak waves resulting from the focusing wave group propagating in finite water depth was also investigated experimentally. Runup, breaking and energy dependence have been investigated. References [1] N.Abcha, N.Leblond(2014), Etude d'une onde solitaire se propageant en présence d'un courant, 14eme congrès francophone de technique laser, Marseille,15-19 septembre 2014. [2] L.Chang et al. (2014), Prebreaking internal velocity field induced by a solitary wave propagating over a 1:10 slope, Ocean Engineering 80 (2014), 1-12.

Surface waves often generate bedforms at the seabed. Small structures such as ripples with a typical wavelength between ten centimeters and one meter are very common structures in the coastal zone. The formation of these structures under nonlinear surface waves is considered in this chapter. Under regular waves, two modes of pattern formation from a flatbed in a wave flume are reported for well-sorted grains and mixtures of grains. Sand ripples can form uniformly or from isolated ripples spreading on the bed while growing. In this latter case, front propagation speed is measured and a simple model based on the quintic complex Ginzburg-Landau equation can explain features of front propagation on the granular bed. The profile of surface waves propagating in shoaling water approaches the solitary waveform before wave breaking. The main characteristics of solitary waves are presented. The effect of the high nonlinearity of these waves may be very significant on bedforms induced in the nearshore zone. The interaction between solitary waves and a sandy bed is reported. Sandy ripples induce a strong energy dissipation of solitary waves. When solitary waves propagate on the background of a standing harmonic wave, bars are formed with crests located beneath the nodes of the harmonic surface wave. In the case of harmonic standing waves alone, the bar crests are positioned beneath the antinodes of the harmonic surface wave. Grains with different densities may be found on the seabed. The concentration of light sedimenting particles on ripple crests is explained by a simple theoretical model.

Khoury, A., Jarno-Druaux, A., and Marin, F., 2013. Experimental simulation of sandy beaches under waves and tides: hydro-morphodynamic analysis Proceedings 12th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 1791–1796, ISSN 0749-0208.--> Numerous studies have been carried out on sandy beach morphology; however, the physical processes which govern beach morphodynamic are still not well understood, despite the significance of this subject in view of the direct applications for coastal erosion. The present work brings a contribution to the study of these processes from well controlled tests carried out in a 10-m-long and 0.49-m-wide wave flume with macro – and mega-tidal regime simulations. The tests were carried out with very fine or fine sand of relative density s=2.65. The incident waves and the free surface in the shoaling zone were measured with resistive probes. The wave breaking height and the free surface in the swash zone were rec...

International audience; The generation of localized, spatially periodic patterns on a sandy bottom is experimentally and theoretically studied. Tests are performed in a hydrodynamic flume where patterns are produced downstream from a vertical cylinder under a steady current. It is found that patterns appear as a result of a subcritical instability of the water-sand bottom interface. A dependence of the area shape occupied by the patterns on the flow velocity and the cylinder diameter is investigated. It is shown that the patterns' characteristics can be explained using the Swift-Hohenberg equation. Numerical simulations point out that for a correct description of the patterns, an additional term which takes into account the impact of vortices on the sandy bottom in the wake of a cylinder must be added in the Swift-Hohenberg equation.

International audience; In recent decades, the study of mechanisms of localized structures formation in non-equilibrium media attracted attention of researchers. Such structures were found in chemically active media, in granular materials, and in many numerical experiments with model equations. In this paper we investigate theoretically and experimentally localized patterns on sandy bottoms arising under the inuence of steady ows in the vicinity of vertical obstacle. Present experiments performed in a hydrodynamic channel show that spatially periodic quasi-stationary patterns whose width increases downstream in the wake of an obstacle arise from a sub-critical instability of the water-sandy bottom interface. We study the dependence of the topology of the area occupied by patterns on the ow velocity. It is shown that the characteristics of pattern on the bottom can be explained using the Swift-Hohenberg equation. Experiments show that for a correct description of structures, supplemented terms which take into account the impact of the vortices arising in the wake of an obstacle must be added into the Swift-Hohenberg equation.

International audience; A large panel of instruments was deployed in the Eastern English Channel to measure the evolution of bedload fluxes during a tidal cycle for two different sites. The first one was characterized by a sandy bed with a low dispersion in size while the other study site implied graded sediments with grain sizes ranging from fine sands to granules. The in situ results obtained were compared with predictions of total bedload fluxes by classical models. A good agreement was found for homogeneous sediments with these formulas. In the case of size heterogeneous sediments, a fractionwise approach, involving a hiding-exposure coefficient and a hindrance factor, provided better predictions of bedload fluxes, but still some discrepancies were noticed. Present results revealed that the consideration of particle shape in formulas through the circularity index enhanced the estimations of bedload transport rates. A new adjustment of Wu et al.’s (J Hydraul Res 38:427–434, 2000) formula was proposed and a very good agreement was obtained between the measured and predicted values.

International audience

Experiments have been performed in a wave flume to analyse the interaction between regular gravity waves and a fixed absorbing semi-immersed breakwater. This breakwater is an improved design of a semi-immersed structure, equipped with impermeable walls at the two ends, by addition of an absorbing caisson at the seaside end of the structure in order to reduce the reflection. A comparison between the two types of breakwater is proposed. The experiments exhibit the great efficiency of such an absorbing breakwater on the reflection characteristics. It is clearly shown that the absorbing caisson also has a profitable effect on the transmission coefficient. The effects of both the immersion and the width of the structure are examined. For the absorbing breakwater it is demonstrated that an increase in the immersion is more efficient than an increase in the width of the structure for both reflection and transmission coefficients. The analysis of the results gives information to choose the dimensions of the absorbing caisson in relation to the wave characteristics. The accurate determination of the higher harmonics travelling in the wave flume is used to analyse the nonlinear behaviour of the interaction between the waves and the structure. The results exhibit a reflected second harmonic with a very large amplitude correlated to the evolution of the reflection coefficient as a function of the relative water depth.

International audience; We report experimental and theoretical results on segregation of particles in sandy bottom under the action of oscillating velocity field due to surface waves. Experiments were performed in-situ and in wave flume. Segregation in the mixtures of light and heavy particles of the same diameter and small and large particles of the same density was observed. It was found that segregation appears on the background of sand ripples generation in the upper «active» zone of the bottom. The thickness of this zone is proportional to the amplitude of velocity oscillation. The topology of segregation patterns depends on particle size differences, on particle density differences as well as on particle percentage composition in the mixture. It was revealed that small particles with small percentage are concentrated below sandy ripples crest. If percentage composition of small and large particles are approximately equal, the large particles are concentrated below the ripples crests. Light particles quite the «active» zone where concentration of heavy particles increases. To investigate the segregation of particles we use non-linear diffusion equations in the presence of gravity field like it was done recently in paper of Fernandez et al (Physica A, 2003, 327, 94–98). The main idea of this model is to take into account the different sizes and densities of particles using mobility coefficients in diffusion equations for concentration of particles. We extended one dimensional model of Fernandez et al for two dimensional case. Numerical simulations demonstrate good qualitative coincidence with experimental data. In particular, zones with high concentration of small and large particles below ripples crest were obtained in numerical simulations depending on percentage composition of particles. Formation of the layer where the concentration of light particles sufficiently decreases was also found in numerical simulations. Importance of segregation processes for biological and environmental problems is discussed.

Particle trajectories and size sorting above an artificial rippled bed under standing surface waves are experimentally and theoretically studied. It is observed that fine particles may be trapped in a very thin region near the ripple crests. When the surface waves damp, fine particles concentrate on the top of ripple crests forming narrow strips, while coarse particles settle more uniformly along the rippled bed. Measurements of particle concentrations before their deposition confirm this size segregation. The present experimental results are explained with a theoretical approach.

International audience; The results of an experimental study of pattern formation on sandy bottom under the action of regular harmonic surface waves are reported. It is found that two modes of pattern formation occur: sand ripples form uniformly on the whole bottom or from localized nucleation sites. In the second regime, the ripples appear in isolated regions patches increasing in size, and front propagation speed is measured. A simple dynamical model based on the Ginzburg-Landau equation is proposed to explain the characteristics of patches.

This work deals with a study of the suspended particles trajectories under standing waves above a fixed rippled bed. Sediment segregation is experimentally observed. It is characterized by different deposits zones for small and coarse particles. When the flow is damping, the small particles concentrate in localized narrow zones on the ripple crests. On the other hand, the coarse particles settle everywhere. A simple theoretical model is developed in order to explain the motion of small particles when the oscillatory flow is damping. We obtain a good agreement between results issued from the theoretical model and the experimental results.

Resume : Ce travail a caractere experimental vise a etudier la dynamique de formation des reseaux de rides de sable en canal a houle. Dans un premier temps, les experiences sont realisees en sollicitant un fond sableux constitue de sediments uniformes en taille avec des conditions de houles regulieres. On etudiera l’evolution temporelle de ces structures a la fois d’un point de vue local (dimensions des rides en terme de longueur d’onde L, hauteur h, cambrure h/L et section S) et d’un point de vue global en termes de statistique du reseau de rides present sur l’ensemble de la veine d’essai (6 m×0,35 m). L’objectif est de caracteriser precisement la croissance des rides et la dynamique du reseau afin d’acceder a la comprehension des processus intervenant au cours de la formation de ce type de structure. Dans un deuxieme temps, les experiences sont realisees avec un fond sedimentaire heterogene en taille. L’influence de l’heterogeneite des sediments sur la croissance des rides est etudiee. Le tri sedimentaire en surface des rides est observe a l’aide de prelevements realises au cours du temps dans la veine d’essai. Une technique experimentale innovante a permis de caracteriser le tri sedimentaire en profondeur pour les deux cas testes.

International audience; This work deals with the dynamics of sand ripples which occur on a flat sandy sea bed excited with an oscillatory flow in a wave flume. The bathymetry of the bed is reported since the first stages of ripple formation with an optical technique. A statistical approach is developed to study the dynamical evolution of ripples. With an identical mobility number and different Reynolds number, two tests leading to 2D and 3D pattern formation are compared. Two stages are detected during ripple formation independently of pattern morphology. However, pattern tridimensionality can be detected with statistical tools. 2D and 3D equilibrium ripple geometric data are compared with the literature.

The dynamical evolution of ripples generated in a wave channel has been investigated using image acquisition techniques. We focus on the evolution with time of ripple geometry. A particular attention has been paid on the method used for the determination of ripple length in the transient stage. Due to the observation of numerous defects in ripple patterns during their formation, a statistical approach has been chosen. Histograms of ripple lengths distribution are processed using Hilbert transform and most probable lengths are estimated. The different stages of ripple formation are characterized by histograms with typical shapes. For some particular conditions, a temporary stable rolling-grain ripple stage can be observed, characterized by a constant most probable length for a short time interval and a constant or slowly increasing steepness. A linear dependence between the length of rolling-grain ripples and the boundary layer Reynolds number is found. In the moderate flow conditions investigated, ripple dynamics is controlled by both, the mobility number and the Reynolds number.