Fine-grained Dredged Material Research Articles

Correlations between index tests and the properties of remoulded clays

Correlations have been developed which relate the compressibility, undrained shear strength, and permeability of remoulded clays to their Atterberg limits and activity. The relationships can be used to model a hydraulic fill, such as fine-grained dredged material or mine tailings, prior to deposition. They can also be used to estimate the engineering properties of normally consolidated natural clay, such as marine sediments. The correlations cover a wide range of plasticity index and liquidity index for a wide variety of clays. It was found that the activity plays a major role in the compressibility and undrained shear strength, and is thus also related to the sensitivity of clays. The activity apparently does not affect the permeability, but other factors remain to be investigated. Because compressibility, undrained shear strength, and permeability are interrelated, it can be concluded that if one is known, then the other two can be derived. Hence, these three engineering properties are seen as different expressions of the same physical phenomenon, rather than as independent variables. Des corrélations ont été dévelopées qui mettent la compressibilité, la résistance à la rupture au cisaillement dans l'état non-drainé et la perméabilité des argiles remaniées en rapport à leur limites d'Atterberg et à leur activité. Ces rapports peuvent s'employer pour modeler un remblai hydraulique comprenant, par exemple, de la matière à grain fin qui a été draguée ou des résidus des mines, antérieurement au dépôt. Ils peuvent aussi être utilisés pour évaluer les propriétés des argiles naturelles consolidées de façon normale, comme représentées, par exemple, par les sédiments marins. Ces corrélations comprennent une gamme étendue des indices de plasticité et de liquidité pour une grande variété d'argiles. On a trouvé que l'activité joue un rôle important dans la compressibilité et dans la résistance à la rupture au cisaillement dans l'état non-drainé, de sorte qu'elle se trouve en rapport à la sensibilité des argiles. Il semble que l'activité n'affecte pas la perméabilité, mais d'autres facteurs restent à examiner. Vu que la compressibilité, la résistance à la rupture au cisaillement dans l'état non-drainé et la perméabilité sont étroitement liées entre elles, on peut conclure que si l'un de ces facteurs est connu, il est possible d'en dériver les deux autres. Ces trois propriétés techniques sont par conséquent regardées comme des expressions différentes du même phénomène physique, plutôt que comme des variables indépendantes.

Land reclamation using fine-grained dredged material : Hartlen, J; Ingers, C Proc 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15–19 June 1981, V1, P145–148. Publ Rotterdam: A. A. Balkema, 1981

Land reclamation using fine-grained dredged material : Hartlen, J; Ingers, C Proc 10th International Conference on Soil Mechanics and Foundation Engineering, Stockholm, 15–19 June 1981, V1, P145–148. Publ Rotterdam: A. A. Balkema, 1981

PHYSICAL PROPERTIES OF CONFINED DREDGED MATERIALS

Physical properties of fine-grained dredged materials from four diverse locations were determined. The results should be useful to those involved in designing, managing, and reclaiming dredged-material-confinement areas. Many of the characteristics of the material were shown to undergo irreversible changes once the materials were dried. Initially, the material behaved like a slurry, but even after one drying, the properties changed so that the materials did not reswell to their orignial volume, the bulk density at a given moisture content was less, and the plasticity index was less. Shrinkage is shown to be linear until the moisture content decreases to about 25 percent. Volume decreases below this moisture content were very small. Relationships are given that allow the use of field-moisture data to determine the amount of shrinkage that has occurred, as well as that which might yet be expected. The saturated and unsaturated permeabilities of all materials are very low, indicating that subsurface drainage will remove only small quantities of water. Physical properties of the materials are most closely correlated with mineralogy and the plasticity index. Those materials with smectitic minerals and greater plasticity indices retained greater amounts of water and had lower permeabilities than materials with other clays or lower plasticity indices.

HYDRODYNAMIC ANALYSIS OF SLUDGE DUMPED IN COASTAL WATERS

Due to increased environmental pressures, there is a rapidly growing tendency to shift from traditional land disposal of dredged material to offshore or ocean disposal. The quantities of such materials are quite large, resulting in a very serious disposal problem. For example, maintenance dredging alone produces approximately six million cubic yards of material annually in Charleston Harbor. Existing techniques are reasonably adequate to describe the transport and settling characteristics of coarse, sandy dredge materials discharged from barges or hopper dredges at sea. However, such approaches need to be modified to describe the transport of fine-grained clay and silt materials. This material constitutes a significant portion of the dredged material resulting from both new harbor and channel construction and maintenance dredging along the coast of the Carolinas and Georgia. These fine-grained materials are subject to many additional physical forces as well as chemical phenomena, e.g., flocculation, salinity and temperature variations, etc. A hydrodynamic model for fine-grained dredged material has been developed which considers many of these forces. It is also applicable for describing the transport mechanisms associated with barge disposal of wastewater sludges from municipal and industrial sources. The results of the model indicate what discharge strategies are necessary for placing the sludge at a desired location or depth with a predetermined concentration.