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Knife spreads terminal silt

DREDGING INTERNATIONAL is using a new cutting device to install 800km of horizontal drains for a forced consolidation project in Belgium.

The company's patented 'Knife' cutter was developed for rapid and accurate laying of multiple horizontal drains. At Geuzenhoek near Kluizen on the Ghent-Terneuzen canal, it is being to create new land for a marine terminal.

The development will be built on three disposal basins currently filled with between 3m and 5m of soft sediment dredged from the canal. Since July, Dredging International, in joint venture with Jan de Nul, has been installing multiple drains on a 1m by 1m grid across each basin.

After temporary flooding to 1m depth, the pontoon mounted cutter is winched back and forth across the basins, simultaneously cutting and laying the 100mm diameter geotextile wrapped PVC drains. The Knife is fitted with up to six adjustable horizontal wings on one side and corresponding attachments on the other to carry the drains. The wings ensure that the drains are placed to within a few centimetres by supporting them until the sediment has closed around them. The number of drains installed corresponds to the depth of sediment, so for a 5m thick layer, five drains are laid on each run.

Once installed, the basins will be capped with 8m of sand overburden to force consolidation. Water will be forced into a collection channel and pumped off site. Complete drainage of the 13ha site is expected to take around a year.

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