Geoscience Reference
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Figure 6.14 Definition sketch of the drop of geotextile containers.
￿
the more evenly the geotextile container is filled (with homogenous sand, in terms
of grain-size distribution and water content, done layer by layer);
￿
the faster the split barge is opened;
￿
the drop (as for granular material) at sea occurs during a current tide window of
less than or equal to 0.5 m/s;
￿
the rougher the surface of the bottom.
For further description and conclusions of the small-scale tests carried out at
Deltares see Appendix H. For the small-scale tests a guidance system was developed
in-house to demonstrate that large geotextile containers can also be accurately placed
at significant depth. For the geotextile containers discussed in this chapter, using such
a guidance system enables highly accurate placements to be achieved. Also, the loads
generated during placement would be considerably lower.
6.6 CONSTRUCTION ASPECTS
The following points are relevant to construction:
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Within the entire construction process, filling is the time-determining factor and
must be performed as quickly as possible. However, the container must be evenly
filled. Dry filling is preferred to hydraulic filling;
￿
Dry filling allows steeper filling, which results in less width for the same filling volume
and allows the geotextile container to more easily exit the split barge during the drop;
￿
For deeper drops (
8 m) “clean” sand is recommended for the fill material. By
internal friction clean sand can absorb a major part of the fall energy that is gen-
erated during impact on the bottom. This significantly reduces the likelihood of
geotextile rupture;
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