Geoscience Reference
In-Depth Information
40
35
above water
below water
30
25
20
15
10
5
0
4
14
6
8
10
12
16
circumference tube cross-section (m)
Figure 5.10
Theoretical required tensile strength of geotextile as a function of the circumference of
the geotextile tube at a pressure during filling of 5 kPa on the upper side of the tube.
The method described below can be used to provide an approximate estimate of
the tensile loads that will occur during the filling process.
Formula 5.6 has to be solved numerically because the shape of the geotextile tube
is unknown before filling. This shape can be approximated using Table 5.3 along with
the radius of curvature. Then formula 5.6 can be used to determine the tensile load in
the geotextile tube.
For example, the radius of the notional circular diameter (
R
) can be calculated
from the value of the tube circumference (
S
).
S
=
10.4 m
⇒
R
=
1.66 m. The desired
height is 2.0 m. This corresponds here with 1.20
R
. The radius of the quadrants on
both sides of the straight basis (
r
) is, after interpolation, 0.45
⋅
⋅
R
(
=
0.74 m), with the
degree of filling
0.81.
If the above example is calculated for placement under water, with an overpres-
sure during filling of 5 kPa and a unit weight (under water) of 10 kN/m
3
, the pressure
in the fill material at the bottom of the geotextile tube is
p
under
≈
=
5
+
2
⋅
10
=
25 kN/m
2
.
The tensile load is now:
T
18.5 kN/m. The difference with the
graphical method is some 10%. This method is therefore suitable to quickly obtain an
indication of the required tensile strength for a selected height.
≈
p
⋅
r
1
=
25
⋅
0.74
=
5.5.3 Stability
The shape (and thus also the deformation) of a geotextile tube plays a key role in
stability control. It is conceivable that a flat geotextile tube is less likely to roll or tilt
than a round one. Also the load on a geotextile in a flat geotextile tube will be lower.
Consequently, it may be considered that a low degree of filling is desirable. However,
a lower degree of filling means a lower height of the tube and consequently, more
