Martin Sanchez

Caractérisation de sédiments marins pour une mise en dépôt à terre et en remblai

ABSTRACT To reuse dredged sludge for earth structures such as unconfined or non embankments, a methodology is proposed to characterize marine sediments. This concerns physical, hydraulic and consolidation properties which constitutes a basis for the design of any embankment with sediments. A series of 8 marine sediments coming from the French Channel coast (2) and Mediterranean sea (6) is studied using different sedimentation, oedometric and creep testing. All the results are analyzed and presented in this paper. The main data are relative to the grain size distribution and Atterberg limits and relationships between permeability and void ratio or concentration. Finally some consolidation data are summarized in comparison with compressible soils.

L'envasement dans les ports: Etudes de cas en Loire-Atlantique

ABSTRACT The distributions of mud deposits and turbidities are studied in the estuary of the river Loire and in the coastal area of Loire-Atlantique (France). A description of the sedimentary dynamics is given in regard to tidal streams and water agitation due to waves. The silting up of the harbour sites is investigated in relation with the environmental conditions and local hydrodynamics associated with the harbour infrastructures. Some configurations are suggested for the implantation of fishing ports and marinas, taking into account economical and environmental conditions. A possible solution for the long term harbour planning in the estuary of the river Loire is suggested; it would induce an important decrease of the maintenance dredgings.

Dynamique des sédiments fins de l'estuaire de la Loire sous l'action de la pesanteur

ABSTRACT This paper presents a global approach of the distribution of the cohesive sediments in the estuary of the river Loire in terms of the velocity of the solid phase. The study covers the large range of concentrations observed in situ. It deals with the settling velocity of suspended matter, the hindered settling velocity of intermediate concentration suspensions and the settlement velocity of fluid mud. The settling velocity W is studied as a stochastic variable. The settlement velocity V is scalar as the sediments in a layer of fluid mud fall with no differential velocity. Finally, it has been observed that the hindered settling velocity is a transition between W and V.

Mobilité des sédiments fins en milieu côtier: Tendances sédimentaires en baie de Bourgneuf

ABSTRACT The distribution of fine sediment deposits in a coastal field near the estuary of the River Loire is presented. Tidal currents and swell heights are described by a numerical 2DH model implemented in this study. A method, based on the study of hydrodynamic forces and their action on fine sediment dynamics, is developed in order to determine the sedimentary tendencies observed in several points of the studied field. The application of this method in an area centred on Bourgneuf bay makes it possible to explain the strong accumulation of fine sediments in this bay and the frequently observed high turbidity produced by resuspension.

Effects of convective-diffusive vertical mixing on the conception of rectangular settling basins

Collection efficiency η of rectangular settling basins is studied in this note for two cases: (i) with no mixing and (ii) with perfect vertical mixing. At first, well known reference solutions corresponding to suspended solids with constant settling velocity are presented. The effects on deposition of suspended solids with varying settling velocities are then studied. Finally, original exact solutions for η are obtained for gamma distributed settling velocities. The reference solutions are perfectly compatible with these more general solutions.

A cost-effective 3D electrical resistivity imaging approach applied to dike investigation

Although DC electrical resistivity imaging is widely applied to dike investigation, either rapid 2D or high-resolution 3D approaches fail to address actual needs. An intermediate electrical resistivity imaging approach referred to as “3D–” is introduced in this paper. The methodology is based on existing tools, and it offers useful and sufficiently reliable 3D images of the investigated structure within a cost-effective and flexible procedure. The survey design, the model discretisation, and the thorough integration of a priori information are the main phases of this procedure. To demonstrate the benefits and limitations of this approach, it is applied to an existing stretch of embankment levee along the Loire River. A numerical study was carried out both on synthetic and real data to assess the 3D imaging capability of the approach and the influence of prior information on the inversion outputs. The important role of a priori information is shown to be even more essential here. The results demonstrate the efficiency and versatility of the 3D– approach for reliable and cost-effective investigations of long dikes.

A Cost-effective 3D Electrical Resistivity Imaging Approach for Embankment Dike Assessment

Although DC-electrical resistivity imaging techniques are efficient tools for embankment dike and levee investigation and monitoring, the complexity of such structures often leads to misinterpretation when conventional 2D procedures are implemented. Nevertheless, fully 3D procedures can be very slow and costly, and bring results and resolution that may exceed the needs. This paper introduces the ‘3D– inversion’ approach that allows a useful and reliable 3D vision of the investigated structure while maintaining an acceptable number of electrodes and data. To compensate the lack of dense 3D data, the approach is mainly based on i) designing data acquisition based on a reasonable number of electrodes and measurements, ii) designing a well-adapted model discretization and iii) inserting as much a priori information as possible. The building process of the numerical model requires attention, particularly on the model discretization. To exemplify this new approach, synthetic results are presented on a model that is a simplification of a real scale experimentation. Preliminary outcomes show the cost-effective potential of the 3D– approach which is to be tested on various case studies in the near future.

A linear method to evaluate energy fluxes in a wave flume

This paper describes an original method to separate two co-existing linear waves in a flume. It is based on the study at a fixed point of the water surface level η, and the slope of the water surface ∂η/∂χ. In this method a complex function containing ? in the real part, and a function obtained from ∂η/∂χ in the imaginary part, is used. This complex function is analysed by the discrete Fourier transform and allows the separation of the two co-existing waves. At the studied point, the amplitudes and phases of the components of the waves propagating towards the positive and negative χ-directions are respectively given by the corresponding amplitudes and phases of the Fourier-series coefficients of positive and negative index frequencies. This method is validated based on a series of tests carried out in a laboratory wave flume