Geoscience Reference
In-Depth Information
in the Netherlands include a scour protection in a river bend improvement in the Waal
at Erlecom (1989), the core of containment dykes of the Naviduct at Enkhuizen Krab-
bersgat (2003) and the core of auxiliary dykes along Enkhuizen-Lelystad (1998). An
extensive description of these projects, can be found in [14, in Dutch]. Numerous
international examples exist of this technique, for example the Incheon Bridge project
[45, 46] and a submerged barrier in Tuscany [47]. In addition, studies have been exe-
cuted to investigate the feasibility of continuous geotextile tubes [27].
Another application using geotextile tubes involves the dewatering of dredged
material to decrease its volume. By selection of the correct geotextile, surplus water
can drain out of the tube and leave behind the solidified soil in the geotextile tube.
This manual focuses on sand-filled geotextile tubes, so for further reference to the drain-
ing of dredged material using geotextile tubes readers should consult Appendix 5.4
from [22].
5.2 INSTALLATIONPROCEDURE
5.2.1 General
A geotextile tube is delivered to the construction site on a roll on a steel pipe. The
geotextile tube is unrolled in the correct location with the inlet and outlet ports centred
vertically on the upper side. Flexible filling ports (made from a suitable geotextile)
with a diameter of around 0.5 m can be placed at a distance of approximately 15 m
relative to each other along the crest of the geotextile tube. However, if the project
desires more filling ports, they can be placed at shorter spacings. The distance over
which a tube can be filled from a single filling port depends on the grain size of the
fill material used.
Filling of a geotextile tube is accomplished by hydraulically pumping a mixture of
sand and water into the tube, see Figure 5.3. The initial amount of sand of the sand-
water mixture entering the tube blocks the geotextile pores to a large extent, reduces
its permeability, and leads to a pressure build up. This leads to a rounded “mush-
room” shape of the geotextile tube. The pumping water drains through the geotextile
skin, and when the tube is nearly filled the pumping water is also drained via the fill-
ing ports. To obtain an even filling height adjacent filling ports may be squeezed to a
greater or lesser degree. To prevent the geotextile tube rolling laterally during filling,
the tube has to be (temporarily) secured horizontally (see Figure 5.2). A slight slope in
the foundation can lead to tilting or rolling. It should be checked that the horizontal
support of the tube does not hinder its sinking when working at some water depth.
The fill material can be pumped into the geotextile tube as a slurry (sand-water
mixture) that generally has a ratio of 1 (solid): 4 (water) to 1:5 (based on volume).
The surplus water flows through the geotextile skin and via the filling ports out of
the tube. It can be determined that if the geotextile tube is filled to around 70% to
80% of its theoretical circular area, the filled height is about half of the 'flat' width of
the geotextile tube (width of the part that comes into contact with the bed). A higher
filling percentage is also possible although this increases the tensile stresses in the
geotextile skin and the tubes are more likely to roll when placed on (slightly) sloping
subsoil [22].
