Typical behaviour during dredging and hydraulic transport

1 Typical behaviour during dredging and hydraulic transport Degradation of particles 

The amount of degradation depends on a number of variables. These may be related to the nature of the fill (carbonate content, original grain size distribution, particle shape, etc.), but also to the operational parameters (type of dredger, number of pumps, length of pipeline, pumping velocity, concentration of the sand-water mixture, etc.). 

Carbonate sands often consists of (fragments ol) shells that are not spherical, but more disk-shaped. This typical shape will influence the behaviour of the particles during hydraulic transport in a discharge pipe. 

Miedema and Ramsdell (2011) demonstrated that the typical disk-shape of shells will reduce the settling velocity of the grains, but increase the erosion velocity required to force settled particles into suspension again. This is caused by the relative orientation of the shells to the direction of the flow during transport and after settlement. 

During transport the particles will preferably expose their smallest cross-sectional area perpendicular to the flow and, subsequently, will tend to settle hke leaves. This will reduce the settling velocity. 

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