Geoscience Reference
In-Depth Information
The energy that has to be dissipated by the geotextile is given in formula (6.4):
=
.k
EEE
geo
477 5
390 59
0
0
J/m
EE
−
=
−
E
al
f
l
l
l
E
ill
f
.
5
390
.
Formula (6.5) can now be used to calculate the strain in the geotextile:
E
90
05 18 3 1000
=
=
geo
10
%
ε
=
05
SJ
⋅
′
′
⋅
⋅
⋅
5
SJ
0
.
The result is still a significant strain percentage but the corresponding tensile
load is 100 kN/m, so a safety factor of 1.4 suffices compared the allowable load of
140 kN/m. In addition, there will be a reduction in the strength (80%) due to the
seams. In this case 140
⋅
0.8
=
112 kN/m. This results in a safety factor of 1.12.
Stability in waves
For geotextile containers on the crest formula (6.14) applies:
H
s
≤⇒
1
⇒
HDH
s
⇒≤
H
s
H
0
99 16
158
58
m
⋅
=
k
.
.
99 1
Δ ⋅
D
s
t
t
k
s
s
t
D
Given the calculated allowable significant wave height, different dimensions must be
chosen for these containers. In many cases no container will be able to be used for the
uppermost units of a structure (because containers cannot be dropped from a barge at the
surface), so a different type of unit will be needed in this location (like a geotextile tube).
For the geotextile containers at a minimum of a single wave height below the still
water line, the formula (6.14) again applies:
H
=
s
2
HDH
k
2
0991
⋅
63
17
≤⇒
⇒
⇒≤
H
s
H
.
17
m
⋅
991
.
s
t
k
s
s
Δ ⋅
D
t
D
With regard to internal sand migration (caterpillar mechanism [37]) and the given
wave height (
H
s
=
3 m) the crest should be at 2
⋅
H
s
or more under water. In this case
it is 2
6 m. The upper part of the construction could be built up using other types
of units, such as geotextile tubes.
⋅
3
=
Stability in currents
According to formula (6.15):
u
0.5 o1.0
cr
<
g
D
t
D
u
≤
0.5 to 1.0
⋅
g
⋅ Δ ⋅
D
⇒
u
≤
0.5 to 1.0
⋅
9.81 0.99 1.6
⋅
⋅
=
1.97 to 3.94 m/s
cr
t
k
cr
