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The DRACULA®-system pushes the limits of hopper dredgers in cemented sand.
CEDA Dredging Days 2005 - Dredging: The Extremes, Rotterdam
Vandycke S., Van den Broeck M. and Thomas K.
Abstract: The D.R.A.C.U.L.A.-system used on trailing suction hopper dredgers was initially designed to dredge stiff to very stiff clay where the integrated high-pressure jets are used to prevent clogging of clay in the draghead and to improve penetration of the teeth in stiff clay. Several projects proved that this system improved production with 20 to 30%.
The trailing suction hopper dredge ‘Lange Wapper’ was recently equipped with the D.R.A.C.U.L.A.-system, not to dredge still clay, but to dredge cemented sand with an UCS-value of 5 to 8 MPa.
For this purpose a standard draghead was modified in order to perform in this hard soil that previously had to be dredged with a cutter suction dredge. The number of teeth in the draghead was reduced in order to have an increased penetration force and every pick point was equipped with a high-pressure waterjet with pressures up to 750 bars. The cemented sand was fragmented in such a way that is was possible for the dredge to pump the dredged soil ashore using its proper pumping system.
The project was at Cadiz (Spain) was executed successfully and all cemented sand was removed up to the required level with the hopper dredge equipped with the DRACULA-system.
Keywords: Hopper Dredge, Cemented sand, waterjet,