Geoscience Reference
In-Depth Information
barge that result in a tensile load in the geotextile. At the start of the opening these
tensile loads are only present in the lowermost part of the geotextile, but just before
the geotextile container leaves the barge it covers a large part of the geotextile surface,
with only the uppermost part being virtually free of loading.
De Groot [36] has evaluated the tensile load in a geotextile during the opening of
the split barge. In most cases, however, this loading is not critical and therefore a sim-
ple formula was developed for a first approximation [4, 15]. The maximum possible
tensile load in the geotextile during the opening of the split barge is:
(6.3)
(
)
T
g A
g
⋅
w
where:
T
=
tensile load in the geotextile [N/m];
ρ
=
density of the geotextile container [kg/m
3
];
g
=
acceleration due to gravity [m/s
2
];
ρ
w
=
density of water [kg/m
3
];
A
=
filled cross-sectional area of the geotextile container [m
2
].
The basis of this formula is the assumption that if just 10% (or less) of the geotex-
tile container lies in the split barge, the container will certainly fall through the open-
ing, at which point the geotextile is subject to the calculated load being 0.9/2
0.45
times the submerged weight of the container. If, according to formula (6.3), the tensile
load is less than the tensile strength of the geotextile, then the load on the geotextile
during the opening of the split barge no longer needs further consideration. Applica-
tion of a safety factor of 1.1 to 1.2 to this design value is recommended.
Given that the longitudinal seams in a geotextile container should be on the upper
side and that this part of the container is the last to leave the barge during the drop, it
is not necessary to account for the lower seam strengths in the above formula.
If the loads generated during opening of the split barge approximate the strength
of the geotextile, and compliance with formula (6.3) is not a straightforward matter, a
more advanced determination of the various loads on the geotextile can be undertaken.
In Appendix F determination of the tensile load in the geotextile at each installation stage
is described.
Based on experience, the following rule for the opening of the barge can be used:
during the drop of the geotextile containers, the split barge must have obtained an
opening of 50% of the total width of the barge bin within 20 to 30 seconds. In prac-
tice, this requirement is not always achievable and even then the barge can still be
used although there is more chance of an uneven drop of the container.
=
6.5.3 Loading on geotextile upon impact on the bottom
When the geotextile container impacts the bottom, the geotextile is subject to a sig-
nificant increase in load and deformation. This has to be determined as accurately
as possible since this is often the critical criterion with regard to the required tensile
strength of the geotextile.
The container fall energy is normally dissipated in two ways: by the strength and
strain of the geotextile and by the deformation of the sand in the container. If the
