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|Mathematical model for predicting the consolidation of dredged material in confined disposal areas
|Johnson, Lawrence D.
|U.S. Army Engineer Waterways Experiment Station.
|Technical Report (Dredged Material Research Program (U.S.)) ; no. D-76-1
|The capacity of containment areas is influenced by many factors that include: (a.) variations in material being dredged; (b.) type of dredge; (c.) volume change on handling the dredged material while dredging and during deposition; (d.) flow velocities of the dredged slurry in the area; (e.) elimination of carrying water by runoff through weirs; (f.) solids in the effluent; (g.) soil permeabilities; (h.) flow patterns and seepage through dikes; (i.) primary consolidation; and (j.) secondary compression effects. Current methods for estimating the capacity of containment areas for placement of dredged material often rely on empirical factors and local experience. From an investigation of various methods for sizing containment areas, suggestions are made for estimating containment area capacity based on consolidation of the dredged material and foundation soils. The capacity of a containment area is defined herein as the total volume of the diked area available to hold dredged material. It is equal to the total unoccupied volume minus the volume associated with the freeboard. The capacity required to accommodate a given volume of in situ sediment to be dredged is related to the volume change characteristics of the sediment. For instance, the volume of sands and gravels deposited in the containment area usually does not change significantly with time and often is the same as, or only moderately more than, that of the in situ material. In contrast, the volume of silts and clays usually increases substantially on dredging and deposition. The subsequent consolidation of these materials can be substantial and lead to significant increases in space available in the containment area for placement of additional dredged material. The volume-time relationships of dredged material are important in predicting the capacity of containment areas and also have considerable impact on subsequent use of deposition areas. Reasonably reliable estimates of the capacity require knowledge of the solids in the effluent water and evaluation of the time rate of change in void ratio of dredged material as it consolidates in the containment area. The usual containment area design does not consider time effects, but uses an empirical bulking factor that relates the volume of in situ sediments to the volume required in the containment area to place the same material. Experience indicates that bulking factors for this purpose vary from about one for most granular materials to as high as two for some fine materials, depending on local conditions. Values below one can occur for loose, granular material or fluffy, fine-grained deposits. A tentative procedure is suggested for the estimation of the volume-time relationships of dredged material in a flooded containment area based on simple sedimentation and consolidation theories. The procedure also includes a method to compute the consolidation of the foundation soils by standard consolidation theory. Laboratory and field investigations are necessary to verify and to develop further the equations and procedures obtained during this study for estimating volume changes with time of various types of sediments accommodated in containment areas. These factors will be investigated in subsequent Dredged Material Research Program studies in order to develop a complete methodology for determining the capacity of a containment area.
|Gov't Doc #:
|Technical Report D-76-1
|Approved for Public Release; Distribution is Unlimited
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