Geoscience Reference
In-Depth Information
For sand-filled systems,
Δ t
=
0.9 to 1.0.
tan
HL
α
=
(the breaker parameter)
ξ
(3.6)
/
0
s
2
gTT
=
(the wave length in deep water)
(3.7)
L
0
2
π
where:
H s
=
significant wave height [m];
D k
=
effective thickness of the geotextile-encapsulated sand element [m];
ξ
=
breaker parameter [
];
t
=
relative density of the structural elements [
];
n
=
porosity of the fill material of the structural elements [
];
α
=
slope [deg];
0
=
wave length in deep water [m];
p
=
peak period [s];
s
=
density of the fill material which is approximately 2,650 [kg/m 3 ];
w
=
density of water (1,000 for freshwater 1,030 for saltwater) [kg/m 3 ].
The effective thickness of the structural elements is partly dependent on the man-
ner in which the units are installed. In Figure 3.3 the two most common installation
geometries are shown (I and II).
The situation shown in the diagram concerns a horizontal placement with approx-
imately 50% overlap between adjacent geotextile bags while the bottom diagram
shows placement where the adjacent geotextile bags are placed against each other on
the slope, comparable with a stone revetment. In the definition of the effective thick-
ness D k , L is the length of the geotextile bag, with the long side perpendicular to the
revetment axis and
the slope of the structure.
According to research, it has been shown [22] that the stability of a structure
with geotextile bags depends on the slope angle, the fill material used the height of the
slope and the nature of the overlap between the bags. No theory is currently available
to deal with all these factors, so a safe approach based on different model tests for a
slope of 1:3 and less is presented here. For this slope:
α
H
D
(for irregular waves, slope 1:3 or less)
(3.8)
14
.
s
Δ
t
D
For steeper slopes, testing has been carried out on field scale in the Große Wellen
Kanal, Hannover, Germany, with bags of 0.15 m 3 volume. The results of these tests
yield the following stability criterion:
H
D
275
ξ
s
(slope 1:3 or steeper)
(3.9)
Δ
t
D
 
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