Geoscience Reference
In-Depth Information
filling of scour holes;
soil protection;
emergency dykes.
The limited dimensions of geotextile bags, compared to larger volume geotex-
tile tubes and geotextile containers, tend to make structures utilizing geotextile bags
relatively expensive solutions. Filling is quite labour intensive. In [14, in Dutch] it is
claimed that the filling and placement of geotextile bags is around 45-75% of the
total cost of a geotextile bag structure. Geotextile bags are therefore used where there
are specific advantages, such as:
there is no requirement to use armour stone. The advantage depends on the una-
vailability of armour stone;
the structure is accessible by swimmers (e.g. at a beach);
the geotextile bags can be placed against other structures, such as piles, with
limited risk of damage;
the structure is relatively easy to remove if it becomes redundant or loses its function.
Optimisation of the fill and installation process lowers the cost of geotextile bag
structures and this is a key goal for all geotextile bag usage.
In many cases, however, geotextile bags are used for relatively small-scale applica-
tions. Partly as a result of this, there has been little systematic research done to gener-
ate design rules for these structures. The literature on the research that has been done
on geotextile bags is summarised in [22].
Temporary geotextile bag structures do not always have to be covered. For per-
manent structures it is necessary to prevent ageing of the geotextile skin by UV light
and the bags are covered with armour stone or other material. When used at greater
water depth (as in scour holes) no cover is needed since the effect of UV light is low
under water. However, a cover layer could be useful against vandalism and other
mechanical damage when the geotextile bags are used as exposed surface protection.
When establishing the appropriate weight and dimensions of the geotextile bags
an important role is played by experience gained from comparable structures in com-
parable situations. In Appendix B “Geotextile bags” of [14, in Dutch] several examples
are given of practical applications with an indication of dimensions and costs. This
presents an initial condition. The designer will have to enter the iterative design proc-
ess; using his initial assumptions of the dimensions, with the formulae presented below
used to check whether or not the structure will be stable under the design conditions.
If it is not stable, the design has to be modified accordingly, and this is also be the case
if the design proves to be over-conservative and further cost savings can be obtained.
3.2 INSTALLATION PROCEDURE
Geotextile bags can be filled in various ways, mechanically or hydraulically, or by
hand.
Placement of geotextile bags can be done using a hydraulic crane equipped with
a lifting frame or large grab, on land or on water. Land-based placement may be