Les sediments marins trouvent leur reemploi avec ou sans traitement dans la construction d’ouvrages portuaires et routiers. Ces applications imposent toute une methodologie pour leur caracterisation hydraulique et mecanique. Cette methodologie est proposee pour le projet SEDIMARD 83 et appliquee a des sediments marins preleves sur 6 sites portuaires de la cote Mediterraneenne. Apres une caracterisation geotechnique elementaire (teneurs en eau initiale, granulometrie, limites d'Atterberg, teneurs en carbonates et matieres organiques) les relations permeabilite - concentration (ou indice des vides) sont etablies a partir d'essais de decantation en colonne et d'essais de consolidation œdometrique. Les essais de decantation en colonne correspondent au tassement sous poids propre du sediment. Les essais de consolidation œdometrique correspondent au tassement de ces memes sediments sous surcharges. Tout d'abord, l'etude des proprietes physiques et chimiques des sediments montre qu'elles varient peu pour une meme region d'origine (Mediterranee). Cependant, un traitement de tri et de separation (sediment brut/sediment dessable/deshydrate) les modifie. L’analyse des resultats des essais de decantation et de consolidation a conduit a l’obtention des parametres classiques de tassement mais aussi a la definition de la relation entre la permeabilite et l’indice des vides. Une continuite a ete bien observee entre les resultats issus de ces deux essais. Translated version: Valorization of Mediterranean sediments in a treatment plant: Study of the geotechnical characterization and permeability The marine sediments find their re-employment with or without treatment in the construction of harbour and road works. These applications impose a complete methodology for the hydraulic and mechanical characterization of sediments. This methodology is proposed for project SEDIMARD 83 and is applied to marine sediments of the Mediterranean coast. After having defined the basic properties of these sediments, column decantation and oedometric tests were carried out on 6 different sediments. The relations between permeability and void index are then deduced. These tests of decantation correspond to a self-weight settlement of the sediment. In order to simulate the consolidation of these same sediments under loading, some oedometric tests were carried out in parallel. First, the physical and chemical properties of these sediments are given and it is shown that certain among them for the same area (the Mediterranean), remain nearly constant. So, dehydration and sieving treatments (raw sediment/desanded sediment/dehydrated sediment) modify them. The analysis led to obtaining the usual settlement parameters of consolidation but also to defining a relation between permeability and void index. Continuity has been well observed between the results issued from these two tests. Keywords: Marine sediment; Physical properties; Chemical properties; Sedimentation; Consolidation; Settlement; Permeability; Desanded sediment.

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Valorisation en unité pilote de sédiments méditerranéens : étude des caractéristiques géotechniques et de la perméabilité

This research work deals with an experimental study on the erosion phenomenon of a mud under the action of a water current. It is observed from research works carried out by Partheniades (J Hydraul Div ASCE 91(HY1):105–139, 1965), Migniot (La Houille Blanche 1&2:11–29, 95–111, 1989), Ockenden and Delo (GeoMar Lett 11:138–142, 1991), Aberle et al. (Mar Geol 207:83–93, 2004), among others, that mud erosion process by an hydrodynamic action depends mainly on sediment properties. Based on a literature study, this critical stress is assumed to be proportional either to the effective cohesion (Eq. 2) or to the yield stress (Eq. 4) of the sediment bed. Six erosion test series have been performed at six different concentrations of a mud from the Loire estuary. Some properties of the tested sediments are: a solid particles density ρs= 2,550 kg m−3, a liquidity and plasticity limit at 140 and 70% of the water content, respectively, a mean size of the dispersed mineral fraction determined by laser techniques of 10 μm, and a volatile matters content of 11.86% by total dry weight burned at 550°C. As the rheological behaviour is difficult to describe, the sediment strength is characterized by only a parameter, namely, the yield stress τy. It is measured with a coaxial cylinder Brookfield LVT viscosimeter following a defined procedure (Hosseini in Liaison entre la rigidite initiale et la cohesion non drainee dans les vases molles—Relation avec la dynamique sedimentaire. These, Universite de Nantes, 167 p, 1999). For each studied concentration, three successive erosion tests are carried out, and for every erosion test, 15 successive measurements of τy are made. The mean values and the standard deviations of τy are shown in Table 1 as a function of the bed sediment concentration C. A confined flume has been conceived and built to characterize the erosion rates. With this device, a current-induced shear stress is generated above an homogeneous deposited sediment (Fig. 1). The bed shear stress τo is calculated from the measured mean velocity V by Eq. 5. The friction coefficient cf involved in Eq. 5 has been evaluated from measurements of the hydraulic pressure loss. Finally, the validity of Eq. 5 has been confirmed by five calibration tests on the incipient of the movement of sands for which results are compared with Shields diagram in Fig. 2. The observed erosion mechanisms affecting cohesive sediments depend mainly on the value of the yield stress. For a fluid mud (τy less than 3 N m−2), the bed shear stress produces at first a wavy motion on the bed surface with a progressive undulation. When the shear stress increases, resuspension produces a diluted sediment cloud which is entrained and dispersed by the flow. For a plastic mud (τy greater than 3 N m−2), erosion occurs by a wrenching of aggregates which are transported near the bottom. Initially, the eroded aggregates measure several millimetres in size; but, once transported, aggregates break into very rigid and compact aggregates of maximum size close to 1 mm in all the cases. During erosion tests, erosion volumetric rates Ev have been evaluated under steady-state bed shear stress τo from the observed variation in time of suspended sediment concentration. A generalized erosion is assumed for Ev≥ Evo= 3 × 10−7 m s−1 (that is the equivalent of 1 mm sediment layer eroded per hour). The generalized erosion occurs above a critical bed shear stress τoe which is linked to τy and mud density through Eq. 7. A phenomenological law defined by Eq. 8 is proposed to calculate the erosion rate as a function of yield stress and hydrodynamic shear stress at the bottom. For τo< τoe, a small erosion is observed, which is described by a formulation given by Cerco et al. (Water quality model of Florida Bay. U.S. Army Engineer Research and Development Center, ERDC/EL TR−00-10, Vicksburg, USA, 260 p, 2000). Above τoe, a small increase in τo produces an important erosion rate rise which is described by a formulation suggested by Mehta and Partheniades (Resuspension of deposited cohesive sediment beds. In: Proceedings of the 18th coastal engineering conference, Cape Town, South Africa, 2:1569–1588, 1982). Figure 3 shows as a function of τo the observed values of Ev (discrete symbols) as well as the proposed model (in solid lines) for the six concentrations. For the theoretically maximum value of Ev, the hydrodynamic shear stress is very high with regard to the sediment cohesion; and then, the water flux produces an entrainment of underlying fluid mud layers. The asymptotic law obtained from the model of Kranenburg and Winterwerp (1997) plotted in dashed lines in Fig. 3, is expressed by Ev= 0.3 u*. A sediment trap inserted in the experimental system allows a sample of eroded mud aggregates to be obtained. It is observed that the maximum value of the diameter DM of the eroded aggregates depends on the density and yield stress of the initially deposited mud according to Eq. 10. In the same way, the density of the aggregates issued from plastic mud erosion is measured following an original experimental method and procedure (Table 3). The erosion of plastic muds with a concentration from 310 to 420 kg m−3 produces aggregates with a concentration close to 400 kg m−3 and yield stress a little greater than 100 N m−2.

Erosion d’une vase de l’estuaire de la Loire sous l’action du courant

Les operations de dragage de sediments sont necessaires pour garantir une bonne exploitation des ports, des voies navigables et des retenues d’eau pour la navigabilite ou pour la production d’energie. Le peu de retour d’experiences positives sur les voies de valorisation a terre des sediments fins de dragage marins et fluviaux revele l’absence de solutions durables. La gestion a terre des sediments fins de retenues hydroelectriques necessite une vision integratrice de l’ensemble des potentialites de valorisation sur le territoire. Une approche durable en matiere de gestion des materiaux de dragage exige notamment un changement de point de vue. Meme si ces derniers ont un statut de dechet, ces materiaux meritent d’etre consideres comme une ressource alternative potentielle qui peut etre precieuse dans un contexte de rarefaction de matiere premiere minerale naturelle. Ainsi, une approche globale adaptee aux sediments de barrages est proposee pour aboutir a la mise en œuvre d’un outil decisionnel de pre-orientation des sediments vers des filieres de valorisation. Un examen de 5 voies de valorisation potentielles, a savoir, en cimenterie, en integration dans le beton, en materiau routier et assimile, en materiau ceramique et en valorisation agronomique, a ete mene avec mise en evidence des specifications d’entree dans le cas des sediments fins de barrage, la recherche des parametres cles, consolidant un inventaire des travaux de recherche et applications dans chaque filiere. Ces 5 filieres ont ete mises en œuvre a l’echelle du laboratoire pour quatre sediments fins provenant de retenues hydroelectriques, representatifs de differentes typologies. Tout d’abord une caracterisation minerale, geotechnique et agronomique a permis de discuter de l’adequation sediments – filieres au regard des criteres d’entree dans les voies de valorisation. S’ensuivent les essais de valorisation i. E. Fabrication d’un clinker, addition de sediments dans un mortier, elaboration d’un materiau routier et confection d’un materiau ceramique, mettant en avant les caracteristiques favorables ou defavorables des sediments fins en relation avec la filiere etudiee. Un outil de decision a ete concu pour pre selectionner les voies de valorisation. Il a ete construit a partir de l’identification et l’interpretation de criteres techniques indicateurs, et a partir d’une caracterisation minimale. Enfin l’accent est mis sur l’importance de prendre en compte la proximite des sites de valorisation possibles.

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Caractérisation des sédiments fins des retenues hydroélectriques en vue d’une orientation vers des filières de valorisation matière

This thesis has addressed the following three main areas of research. 1) The physico-chemical characteristics of eight selected estuaries on the south coast of Western Australia that represent different estuary types, 2) the ichthyofaunal characteristics of the basin and riverine regions of offshore, deeper waters of five of those estuaries and 3) aspects of the biology of the iconic Black Bream Acanthopagrus butcheri in each of those estuaries in which it was abundant.

Although four of the estuaries on the south coast of Western Australia remain permanently open to the ocean, the others only become open when the volume of river discharge is sufficient to breach the prominent sand bars that form at their mouths. The sand bars of the latter estuaries are breached either annually following heavy winter and early spring rainfall (seasonally-open estuaries) or infrequently after exceptionally heavy discharge (normally-closed estuaries). The work for this thesis was undertaken in the permanently-open Oyster Harbour, the seasonally-open Broke, Irwin and Wilson inlets and the normally-closed Wellstead Estuary and Hamersley, Culham and Stokes inlets, which are all located within a ca 500 km stretch of coastline.

In permanently and seasonally-open estuaries, pronounced haloclines and oxyclines were present in their narrow riverine regions, but not in their wide basins where the waters are subjected to wind-driven mixing. The extent of cyclical seasonal fluctuations in environmental conditions differed markedly among the three seasonally-open estuaries and between years in one of those systems. These differences reflected variations in the relationship between the volume of fluvial discharge, which is determined by a combination of the amount of local rainfall, catchment size and extent of clearing of native vegetation, and the amount of intrusion by marine waters, which is largely controlled by the size and duration of the opening of the estuary mouth. The mean seasonal salinities in the basins of three of the normally-closed estuaries increased over three years of very low rainfall to 64 in the deepest estuary (Stokes Inlet) to 145 in Hamersley Inlet and to 296 in the shallowest estuary (Culham Inlet). Gill netting seasonally for two years at sites in the basin and saline lower reaches of the main tributary of the seasonally-open Broke, Irwin and Wilson inlets, the permanently-open Oyster Harbour and the normally-closed Wellstead Estuary yielded 22 329 fishes representing 58 species. Overall, and irrespective of estuary type, the species compositions of the basins and rivers differed markedly. This was attributable to consistently greater abundances of Mugil cephalus, and usually also of A. butcheri, in the riverine region of each estuary and to the restriction of a range of species largely to the basins. However, the ichthyofaunal compositions in the basins of the five estuaries varied markedly, reflecting, in part, differences in the extent and duration of the opening of the estuary mouth and/or whether extensive growths of macrophytes were present. Changes in the ichthyofaunal composition of the normally-closed Wellstead Estuary between the first and second years of the study were attributable, in particular, to the movement of two mugilid species into offshore waters as they increased in size. Cyclical changes in ichthyofaunal composition were conspicuous in both the basin and riverine regions of the estuary that underwent the most pronounced seasonal variations in environmental conditions. In each estuary, species richness was greater in the basin than river, where salinities were more variable and fell to lower levels and were thus less conducive to the immigration of most marine species. Catch rates were least in Broke Inlet, which had the lowest primary productivity, and were particularly high in Wellstead Estuary, which is highly eutrophic.

The maximum ages of Acanthopagrus butcheri ranged downwards from 13 to 15 years in Wilson Inlet, Wellstead Estuary, Culham Inlet and Stokes Inlet, 9 years in Oyster Harbour and only 5 years in Irwin Inlet and Hamersley Inlet. Growth of A. butcheri varied markedly among the various estuaries, probably reflecting differences in the density of A. butcheri, quality/quantity of food and/or salinity regime. The relationship between fish length and otolith radius varied between sexes and among estuaries. The width of the annual growth zones of otoliths was shown, however, to vary among years, particularly in Stokes Inlet, in which the growth zones were widest in years of relatively high rainfall and thus when salinities were presumably below that of full-strength sea water. The trends exhibited throughout the year by the gonadosomatic indices and the prevalences of each of the sequential stages in gonadal development demonstrate that A. butcheri spawns mainly in spring in estuaries on the south coast of Western Australia. The lengths at maturity (L50s) of A. butcheri in the four estuaries from which it was possible to obtain substantial reproductive data were not significantly different (all p > 0.05), with the values for females, for example, ranging only from 146-161 mm. While no fish matured at the end of their first year of life in those estuaries, the majority of fish did mature at the end of their second year of life (73-100%). The vast majority or all fish were mature by 200 mm, which is well below the minimum legal length (MLL) for retention of this species in Western Australia, thus providing the potential for all fish that survive to the MLL to reproduce before being legally retained. Recruitment of A. butcheri varied markedly among years and estuaries. Recruitment in the seasonally-open Wilson Inlet was greatest in years of below average rainfall and thus presumably also relatively elevated salinities and reduced stratification and associated deoxygenation of the bottom water layer in the rivers. Although massive mortalities of A. butcheri in two of the normally-closed estuaries prevented comparisons across this estuary type, it appears that strong recruitment in these estuaries is related to years of relatively high rainfall and presumably the lowering of salinities in these estuaries to below that of full-strength sea water. Total mortality (Z) of A. butcheri appeared to be slightly higher in estuaries with the greatest fishing pressure.

The species composition and diversity of the diets of A. butcheri in three normally-closed estuaries, i.e. Hamersley, Culham and Stokes inlets, which vary markedly in the extents to which they become hypersaline during dry periods, were compared. Although a wide range of taxa, including macrophytes, polychaetes, molluscs, crustaceans, insects and teleosts, were ingested by A. butcheri in each estuary, the frequencies of ingestion and volumetric dietary contributions of these taxa varied greatly among the fish in these estuaries. Thus, for example, relatively greater contributions were made to the diet by polychaetes and crustaceans in Stokes Inlet, by macrophytes in Hamersley Inlet, and by insects (mainly chironomid larvae) in Culham Inlet. The relatively greater contribution of teleosts to the diets of A. butcheri in the Hamersley and Culham inlets than in Stokes Inlet, and also differences in the main teleost species ingested in the first two estuaries, are consistent with differences in the densities of fish overall and of the main fish species in those estuaries. The diversity of the diet was far greater in Stokes Inlet than in the other two far more variably saline estuaries, presumably reflecting a greater diversity of food. The dietary compositions of A. butcheri in upstream pools in the tributary of Culham Inlet, which offer refuge when salinities increase markedly in the main body of the estuary, differed from those in downstream regions, further emphasising the opportunistic nature of the feeding behaviour of A. butcheri. The dietary compositions of A. butcheri underwent size-related changes, but the taxa contributing most to those changes varied greatly among estuaries. Size-related changes would be particularly beneficial in reducing intraspecific competition for food in the two estuaries that vary greatly in salinity and would thus be likely to contain a less diverse range of prey.

 In summary, this thesis has demonstrated that the physico-chemical characteristics of estuaries on the south coast of Western Australia vary markedly even among estuaries of the same type, i.e. seasonally open and normally closed, and has elucidated the basis for those differences. While the characteristics of the ichthyofaunas in the offshore waters of the various estuaries on that coast differ markedly, those differences were not as marked as the overall difference between the basin and riverine regions of those systems. Finally, the iconic Black Bream Acanthopagrus butcheri is characterised by very different growth and recruitment patterns in the various estuaries and highly opportunistic feeding behaviour. The great plasticity of A. butcheri helps account for the success of this species in the range of very different environments found in south coast estuaries.

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Characteristics of the ichthyofaunas of offshore waters in different types of estuary in Western Australia, including the biology of Black Bream Acanthopagrus butcheri

Ainsi, a partir d'essais de tassement realises en laboratoire sur des boues d'origines tres diverses, CARRIER et al. [2] determinent que pour des buts pratiques, on peut considerer que la limite entre les phenomenes de sedimentation et de consolidation correspond a une teneur en eau egale a 7 fois la limite de liquidite du materiau, soit une concentration Co donnee par: ce cas, caracterise par la presence des contraintes effectives, une partie des contraintes est transmise grain a grain et donc, la vase est en etat de depot.

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Modélisation du tassement sous poids propre des couches de vase molle et saturée, sur un fond imperméable

Une consequence des travaux d'amenagement realises dans les estuaires est la modification de l'hydraulique, ce qui affecte la dynamique sedimentaire des vases en creant des zones qui s'engraissent et d'autres qui s'erodent. La modelisation numerique permet de prevoir toute modification hydraulique liee aux travaux d'amenagement avec une assez grande precision. En revanche, du fait de la complexite du probleme, les modeles hydrosedimentaires, meme les plus performants, donnent des resultats plus qualitatifs que quantitatifs et ne permettent pas de repondre a un certain nombre des questions pratiques que peut se poser un ingenieur. Le but de cet article est d'etudier le lien entre les travaux d'amenagement de l'estuaire de la Loire, l'hydraulique, et les problemes d'envasement et d'erosion observes dans differents secteurs de l'estuaire. Ceci est possible par l'utilisation de methodes simples, grâce a la modelisation des principaux processus sedimentaires en jeu (transport, depot, tassement, erosion).

Impact sédimentaire des travaux d'aménagement de l'estuaire de la Loire

The self-weight seulement of mud is a sedimentary process acting on bed soUd concentration and consequently on bed erosion rates. The paper concernsa simple modelling of mud seulement in order to consider this process in mathematical hydro-sedimentary simulations. A proposed mode! takes into account the mechanical phenomena with the typical properties. This approach simplifies a multi-parameterhydro-sedimentary modelling. The variability of permeability coefficient with soUd concentration is the main factor considered. The validity of the presented model has beenproved by a great number of applications on varied materials (Sanchez, 1992). FinaIly, this model offers two possibilities :firstly to appreciate the soUdconcentration above which the sediment is gathering near the bed to possibly give a lens-shaped body of pseudo-plastic mud, and secondlyto detect the /imu cases where the seulement is occurring quickly. Resume

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Le tassement des vases comme processus sédimentaire

Des mesures des niveaux de basses mers realisees par les autorites portuaires dans l'estuaire de la Loire montrent qu'entre 1969 et 1993 ce niveau est descendu d'une facon significative. Ceci s'explique par les dragages recents dans le chenal externe de l'estuaire qui ont modifie la propagation de la maree dans ce site, ce qui a conduit a une correction officielle de –0,40 m pour le zero des cotes marines.

Modification de la marée par le creusement du chenal d'un estuaire

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Alain Grovel

Papers

Modélisation du tassement sous poids propre des couches de vase molle et saturée, sur un fond imperméable

Impact sédimentaire des travaux d'aménagement de l'estuaire de la Loire

Le tassement des vases comme processus sédimentaire

Modification de la marée par le creusement du chenal d'un estuaire

Problèmes d'un estuaire aménagé la Loire. Vers une recherche de solutions concertées