Geoscience Reference
In-Depth Information
Figure 4.1 Use of a geotextile mattress as bank protection at
Nageler Vaart (The Netherlands).
the geotextile mattress in the vicinity of the seams comprises only two geotextile layers
and is thus at that location quite thin and permeable, the hydraulic gradient on the
filter and the subsoil is therefore relatively high. In such a situation the critical values
for the hydraulic gradient and velocity may be exceeded and this may cause local
displacement of the base material. By filling the sausages to the maximum volume the
seams are under tension and the average thickness of the mattress increases. Proper
installation ensures the hydraulic gradient on the filter is reduced and any subsequent
displacements minimized.
Maximum sand density inside the mattresses also has the effect that internal sand
compaction is maximized and movement by waves and currents is minimized. Mat-
tresses always need to be anchored on the upper side to prevent sliding down the
slope. This is done with the use of an anchor trench.
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