Geoscience Reference
In-Depth Information
H
D
R
H
(for uppermost elements)
(3.10)
0790
09
s
≤
+
c
.
790
+
Δ
t
D
s
where:
R
c
is the distance between the crest and the still water line, but is zero when the
crest is below the still water line.
3.5.4 Stability when subject to longitudinal
current flows
To determine the stability of geotextile-encapsulated sand elements when subject to
longitudinal current flows (current flow parallel to the structure, see Figure 3.5), as
in the application for canals and rivers, use can be made of the Pilarczyk relationship
[23], based on a fully protected foundation of sand:
2
Φ
K
T
u
Kg
s
Δ
Thcr
(3.11)
D
≥
0 035
⋅
t
k
.
2
Ψ
s
where:
D
k
=
effective thickness of the geotextile-encapsulated sand element [m];
t
=
relative density of the geotextile-encapsulated sand element -
see formula 3.5 [
−
];
cr
=
critical horizontal flow velocity along the surface of the structure [m/s];
Φ
=
stability parameter, depending on the application [
−
];
Ψ
=
Shields parameter [
−
];
T
=
turbulence factor [
−
];
h
=
factor related to the depth [
−
];
s
=
factor related to the slope angle [
−
].
For the stability parameter
Φ
the following values apply:
for continuous top layer:
Φ
=
1.0;
for edges:
Φ
=
1.5.
Figure 3.5
View from above of longitudinal current flow in a geotextile bags structure.
