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 ERDC TN-DOER-I3
July 2000
The slurry density is typically measured by a nuclear density source located on the dredge discharge
pipeline. The slurry density measurement provides a complete record of the dredging operation. It
provides data on the average slurry density when the suction head is engaged in material, the average
slurry density during the overall dredging cycle (for a cutterhead dredge), and the cycle and overall
dredge efficiency. The following section details how each part of the dredge cycle can be analyzed
to evaluate dredge performance during the project.
Dredge Cycle Analysis. For the purpose of this analysis, the cutterhead dredging cycle consists
of when the dredge swings into the material, completes the swing, and advances the dredge. When
the dredge is engaging the material, solids entrainment is limited by suction line losses and cutface
height. The average density while the cutterhead is engaged in the material is calculated to be:
N
∑ ρs
ρmat = 0
(1)
Ncyc
where
ρmat
= the average slurry density while in material in g/cm3
ρs = measured slurry density in g/cm3
Ncyc = number of data points
This represents the maximum capability of dredge in removing and transporting solids given project
constraints such as the bank height limitation and flow conditions. The cutface height generally
dictates the maximum amount of material that can be removed when the cutterhead is engaging
material. If the cutface height is small, which is typical for maintenance dredging projects, the solids
content of the slurry conveyed by the dredge will be reduced. As a rule, if the bank height is on the
order of the diameter of the cutterhead or greater, ample material will be available for loading the
suction pipe, and therefore maximizing solids content and dredge production.
The overall average cycle slurry density represents an average of the slurry density when the
cutterhead is engaged in material, and when the dredge is advancing, at which time only water is
being pumped. This cycle overall average density is represented by:
N
∑ ρs
ρcyc = 0
(2)
N
where
ρcyc = the average slurry density over the cycle in g/cm3
N
= number of data points
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