Geoscience Reference
In-Depth Information
For the drop of geotextile containers it is desirable for the split barge to fully open
(50% of the width of the bin) within 20 to 30 seconds;
The use of unsaturated sand (which contains air enclosed in the pores) as fill material
is preferable because it temporarily provides more resistance to the deformation asso-
ciated with impact and thus decreases the loads on the geotextile. Further, unsaturated
sand has the advantage that the submerged weight of the geotextile container is lower
and thus the fall velocity and fall energy are less than when saturated sand is used;
To be able to place the geotextile containers as accurately as possible, a thorough
drop plan must be drawn up. In view of the increasing difficulty of placement
accuracy at greater water depths, it is this area that demands most attention;
Geotextile containers should be dropped within the tide window. This increases
the placement accuracy.
6.7 CALCULATION EXAMPLE
Situation
The case concerns a breakwater that will be constructed using geotextile containers.
The containers will be dropped from a split barge. The following is known:
maximum water depth is 10 m;
length of the bin of the split barge:
l
=
29.5 m;
maximum opening width of the split barge:
b
0
=
3 m;
filled cross sectional area in the horizontal plane:
A
s
=
100 m
2
;
fill material: sand;
porosity of the fill material:
n
=
0.4 [
−
];
geotextile: woven polypropylene (PP), maximum allowable tensile load in the
geotextile
T
m
=
140 kN/m;
geotextile: tensile stiffness:
J
=
1000 kN/m;
drag force coefficient of the geotextile container:
C
d
=
1.0 [
−
];
container dropped when there are no currents and waves;
significant wave height
H
s
=
3 m;
current velocity
u
=
0.8 m/s.
Required
Determine the required tensile strength of the geotextile for the various load situa-
tions. Assess the stability in waves and currents, the stability of the container stacking
and the placement accuracy.
Calculation
Shape and dimensions of the geotextile container
Based on Table 6.1 and the split barge bin length of 29.5 m, the following dimensions
of the geotextile container are used:
degree of filling of the bin:
f
=
0.8 (80%);
container volume:
V
=
320 m
3
;
