SEDIMENTATION AND CONSOLIDATION OF

A HIGH WATER CONTENT SOIL

ALEXIS Alain[1], LE BRAS Gilbert[2]

ABSTRACT

  The permanent siltation of harbours and estuaries has led  their administrative companies to undertake  dredging operations in order to guarantee a minimal water depth required for  free access to port infrastructures. This long and expensive work interferes with the port trade. Dredged material is injected into the sea with the creation of a maritime dump or stocked on earth in basins. In each case, there will be a formation of a high water content soil.  This paper deals with the geotechnical formation of high water content soils by means of an experimental laboratory sedimentation/consolidation bench.  We have devised and realized a controlled bench which allows us to analyze the natural soil formation under self weight. The tested soil  settles in sedimentation/consolidation columns (1.5 m. in height, 100 mm in diameter). Pressure and density measurements in the tested soil are possible on the whole height of the vertical column. Values of density are obtained by gamma-densimetry. The precision of the measurements is +/-0.5% for the density and +/-3 Pa for the pressures. Each test is performed over 32 days with 17 intermediate times.  An originality of this bench lies in the fact that it allows measurements with a good precision in density and pressure at a very early state of soil formation (first values at 1.33 min. from the beginning of the test).  The test we are presenting concerned the natural mud found in the Loire estuary (France) prepared to an initial concentration of 200 g/ l (density 1.135).  These measurements are studied in terms of  evolution of total stress, excess pore pressure, void ratio and effective stress as related to time.  For this test, we present the density and pressure measured profiles as well as the deduced effective stress curves, paths of particles and rates of consolidation.  On a void ratio versus effective stress diagram, we clearly show the evolution of soil consolidating under self weight during the intermediate phase of its formation.  The results of this study will greatly help in understanding the way soils and deposits behave in their environment.

Key Words: High water content soils, Sedimentation/consolidation, Density, Pore pressure, Effective stress, Particle trajectory.

BACK

Development of a surface plume model and its application to sediment transport modelling OF DREDGING in coastal waters

Y. Chen ^[3], P. A. MACKINNON [4] and G. Thompson [5]

ABSTRACT

  The dredging operations of trailing suction hopper dredgers discharge large quantities of fine sediment into the water and can cause a substantial increase in suspended sediment concentration, resulting in the formation of visible surface plumes. This paper describes the development of a new surface plume model for the sediment transport modelling of marine dredging. The model is based on the analytical solutions of the horizontal advection and dispersion-diffusion equation and is suitable for unsteady flows in the marine environment. The newly developed model has been applied to a proposed marine dredging feasibility study in Hong Kong to demonstrate the possible model applications.

Key Words: Surface Plumes, Sediment transport, Dredging, Mathematical models,  Analytical solutions, Water quality

BACK

.

MATHEMATICAL MODELS FOR LIQUID-SOLID TWO-PHASE FLOW

Weiming Wu and Sam S.Y. Wang[16]

ABSTRACT

  The governing equations, interphase actions, constitutive relations and turbulence closures of the two-fluid model and diffusion model for the liquid-solid two-phase flow are studied in this paper. The pressure actions in and between two phases are analyzed, and the governing equations of the two-fluid model are conveniently closed by adding the interphase pressure-difference force into the pressure terms of momentum equations. The constitutive relations for the liquid-solid mixture in the diffusion model are given by the models of Newtonian fluid and Bingham fluid, and the Bingham relation of shear stress and deformation rate for the single-directional shear flow of the mixture is extended to a general form for the multi-directional shear flow. The equation for the interphase velocity difference, which is used to close the generalized diffusion model, is derived from the momentum equations of two-fluid model and then simplified to more useful forms. For the turbulent flow, the mean movement equations of the two-fluid model and diffusion model are derived by using Reynolds averaging method. The closure techniques for the mean movement equations on the levels of zero-order turbulence model and k-e turbulence model are suggested. This paper presents the general basis of the mathematical models, which is to be followed by their validations and applications in the near future.

Key Words: Liquid-solid two-phase flow, Diffusion model, Two-fluid model, Governing equations, Interphase actions, Constitutive relations, Continuous medium, Newtonian fluid, Bingham fluid, Turbulent flow, Reynolds averaging method, Turbulence models, k-e turbulence model

 BACK

EXPERIMENTAL STUDY ON FALL VELOCITY

OF NON-UNIFORM SEDIMENT IN FLOWING WATER

Han Wenliang, Gao Guoming, Wang Guangqian and Hui Yujia[6]

ABSTRACT

  A conical settlement barrel is used to study the group fall velocity of non-uniform particles, which allows the current to flow from the bottom to the top, with particles suspending in the flow.  The average flow velocity at the cross section is regarded as the settling speed of the particles. A formula of group settling velocity for non-uniform particles is obtained by analyzing the experimental data. Also, a preliminary study on the group fall velocity of each size of non-uniform particles is carried out, and fall velocity formulas for various size groups are obtained. The group settling velocity formulas agree well with various data for non-uniform particles with relatively high reliability and accuracy.

 Key Words: Non-uniform particles, Fall velocity, Concentration, Non-uniform coefficient

BACK

SEDIMENT LOAD AND ITS INFLUENCE ON CHANNEL PROCESSES

OF SOME LARGE RIVERS IN RUSSIA AND CHINA[7]

LIU Shuguang[8]^,, CHALOV R.S.³ , WU Dandan⁴, LI Congxian⁵

ABSTRACT

  The sediment load, particle size distribution, and ratio between suspended and bed load components are analyzed for some large rivers in Russia and China. The relationship is shown between the longitudinal changes in sediment load and the directions of vertical river channel deformation, i.e. river incision or sedimentation, which in turn are supported by results of analysis of long-term stage discharge curves. It seems that branching channels are common for the rivers, except where the sediment load is great (such as in the Yellow River).  Conditions for forming different types of river channels are defined with the help of diagrams showing the “water discharge-slope” and “slope- sediment concentration” relationships.

 Key Words: Sediment load, Channel processes, River pattern, Russia river

 BACK

 A REVIEW OF RESERVOIR DESILTATION

S. Anders BRANDT[9]

  ABSTRACT

  Reservoir sedimentation is a growing problem around the world. The existing literature on reservoir desiltation has, therefore, been systematically examined and evaluated. The review is divided into three topics dealing with different aspects of reservoir desiltation. The first topic treats different hydraulic reservoir desilting-techniques. The emphases are put on flushing of already deposited sediment and routing of incoming sediments from upstream, through a reservoir, but alternative methods, such as transporting sediment through flexible pipes and siphoning, are also described. The second topic treats resulting reservoir geomorphology after hydraulic reservoir flushings. This includes cross-sectional and longitudinal variations in geomorphology due to flushing, but also the available literature on physical and analytical models. The third topic treats downstream geomorphological and sedimentological effects during and after reservoir flushing operations. Attention is given to water flow-, sediment concentration-, and deposition patterns, as well as transported and deposited sediment characteristics.

Key Words: Desiltation efficiency, reservoir flushing, density-current venting, sediment sluicing, erosion pattern, downstream effects, flow characteristics, sedimentation

BACK

ASPECTS OF RIDGING AND CROPPING FOR GULLY RECLAMATION

 K.M. IBE[10] Sr. AND Th. M. BOERS[11]

ABSTRACT

  The history of a gully which developed on a slope at the campus of the Federal University of Technology, Owerri,  Nigeria is briefly discussed.  Civil engineering measures were taken to cut off the upstream catchment area, close the gully with bulldozers and construct contour bands to divide the slope in sections.  Subsequent agricultural development of the area had not been completed which continued the threat of renewed gully formation  An experimental field was established on the 2 ha slope where field trials were set up of ridging and cropping to develop proper methods to complete the gully reclamation process.  The selected cropping patterns for different sections of the field and problems encountered in the research are discussed.  Some concluding remarks and recommendations are made: 1) Hydrology 2) plant protection 3) agronomy at the Federal University of Technology, Owerri – Nigeria.

BACK

HOW ONE-D AND TWO-D MODELS COMBINED?

-Discussion on “One?D and two?D combined model

for estuary sedimentation” by Zhang Shiqi[12]

 C.B. Singh[13] and L.K. Ghosh[14]

  The author is appreciated for his commendable work on combining one dimensional and two dimensional mathematical models of hydrodynamics and sediment transport for an estuary wherein complicated evolution process of the Yellow River mouth is successfully simulated. The highlights of the so called integrated models are the incorporations of special treatment dealing with continuous boundary and friction at moving bottom with the help of empirical formula instead of Manning’s roughness and the effect of  flocculation of fine sediment particles (D₅₀ ranging between 0.01 to 0.04 mm and maximum sediment concentration being 80 kg/m³).  The numerical scheme of the 2D & 1D models are ADI and Double sweep techniques respectively.  The model is verified by using a set of measured field data. In the governing equations of conservation as well as empirical formulae, all the terms representing runoff, tide induced current, wind induced current, effect of wave and even the effect of flocculation of sediment particles are considered.

BACK

 DEVELOPMENT OF RIVER AND ESTUARY SEDIMENT MODELS*

-Response to the discussion by C. B. Singh and L. K. Ghosh

Zhang Shiqi[15]

  Mr. Singh and Mr. Ghosh have carefully reviewed and made valuable suggestions and comments. The author would like to express his gratitude to them.  The explanations to the comments and some details of the model development are as follows.

BACK