Geoscience Reference
In-Depth Information
Following this, the economic feasibility is evaluated. Where possible, this should be
done in consultation with the operator or contractor.
The thickness of a geotextile bag is not clearly defined, with various methods
referred to in the literature. Since the element is flexible, the thickness can also change.
For rectangular and more or less round geotextile bags a theoretical diameter can be
used (analogous to what is normal for rubble) as if the bag is a cube. The thickness of
the bag is then the equivalent to the side of the cube, i.e:
(3.1)
3
DV
n
where:
D
n
=
nominal thickness of the geotextile bag [m];
V
=
volume of the geotextile bag [m
3
].
For more elongated bags (see Figure 3.2) the above formula would result in an
excessive thickness. For well-filled elongated bags the nominal thickness can be better
derived using the cross-sectional area as a basis:
(3.2)
DA
n
where:
A
=
cross-sectional area of the geotextile bag perpendicular to the longest
axis [m
2
].
3.4
FAILURE MODES AND SAFETY CONSIDERATIONS
When designing a structure with geotextile bags, the following potential failure modes
must be taken into account:
rupture of the geotextile due to impact on the bed;
insufficient seam strength;
instability of the geotextile bags through wave attack;
instability of the geotextile bags through water current along the structure;
instability of the geotextile bags through water current over the structure;
instability of the geotextile bags due to wave attack;
foundation failure and deformation;
liquefaction of the geotextile bag fill.
In the final design phase a safety factor of 1.1 to 1.2 is recommended for geotex-
tile bags in relation to the design value.
During the construction phase, higher factors of safety may be recommended
for specific failure mechanisms, especially when the safety of personnel is involved.
The dynamic effects associated with filling, loading and installation of the geotextile
bags may justify a safety factor as great as 5 for installation effects.
