Geoscience Reference
In-Depth Information
This tensile load has to be less than or equal to the required tensile strength of the
seams in the geotextile container.
When the required impact tensile load is greater than the tensile load calculated for
release from the split barge, then the impact condition governs the required tensile strength
of the geotextile container. The strength of the seams is the weakest component and this
will govern the tensile strength and the corresponding strain. This has a major influence on
the result of formula (6.6) (see also the calculation example at the end of this chapter).
6.5.5 Stability in waves
In [5] the development of design formulae for the stability of geotextile containers under
wave attack have been given. In a small-scale (1:20) model two different structures
were tested, both of which were stacked at a slope of approximately 1(V):3(H), with
the difference being the degree of filling of the geotextile containers (46% versus 70%).
Based on the results of this model study the following design formula can be given for
the stability under wave load of individual geotextile containers with
b/D
k
>
4:
H
b
if
(6.13)
s
2
b
4
≤
b
>
Δ⋅
t
D
D
k
t
D
where:
H
s
=
significant wave height [m];
t
=
relative density of the geotextile container [-];
D
k
=
effective thickness of the geotextile container after drop [m];
b
=
width of the geotextile container after drop [m].
In [22, see paragraph 5.4.11] a comparable ratio is given for the stability of geo-
textile containers under the influence of wave attack:
H
(6.14)
s
F
≤
Δ⋅
t
D
t
D
where:
F
=
1 for geotextile containers on the crest of the structure and lying less than the
depth of
H
s
under water, as in tidal areas [-];
F
=
2 for geotextile containers that lie lower than the depth of
H
s
beneath the still
water line [
−
].
During large scale physical model tests on the stability of geotextile containers [37],
performed by Deltares, it was observed that besides sliding, the 'caterpillar' mecha-
nism (caused by the migration of sand in the container) is a significant mechanism. The
stability of the geotextile containers in the large scale tests was lower than the stability
determined in other (smaller) scale model tests. This is explained by the migration of
the sand being better modelled in large scale tests than in small scale tests.
Van Steeg and Klein Breteler [37] have concluded the following; the application
of geotextile containers is limited to areas with low wave attack (
H
s
<
0.75 m with the
