Geoscience Reference
In-Depth Information
1
2
(6.5)
2
E
S J
ε
S J
⋅⋅
S J
geo
m
2
where:
S
=
circumference of the geotextile [m];
geo
=
maximum energy to be dissipated by the geotextile per unit of length [kJ/m];
ε
m
=
maximum strain of the geotextile [-];
J
=
tensile stiffness of the geotextile [kN/m].
Formula (6.5) can also be rewritten as:
1
(6.6)
E
S T
ε
⋅
T
⋅
geo
m
S T
m
2
where:
m
=
tensile load in the geotextile [kN/m];
ε
m
=
tensile strain in the geotextile [
−
].
This formula assumes a linear load-strain behaviour and since, in practice, the
geotextile reacts less stiffly initially and more stiffly at greater strains, this is an unsafe
approximation, but acceptable since the assumption that all kinetic energy is dissi-
pated by the geotextile is on the safe side. At maximum tensile strength the stiffness
decreases again and the formula may become conservative. However, that value is
never reached in practice since the seams will break before this value is reached.
The strength of the seams and the fastening quality of the closing on top of the
container are normally the limiting factors. If the tensile strength of the seams is half
that of the actual geotextile (see Table 2.5), the
ε
m
is normally also half of the value
for the entire geotextile (and the energy that can be dissipated is thus just a quarter
of the geotextile itself). This demonstrates that the quality of the seams for geotextile
containers is crucial. For calculation, it is recommended to use a safety factor of 1.1
to 1.2 on the design value. It should also be noted from this formula that the circum-
ference (
S
) is directly related to the amount of energy that can be dissipated. Thus,
a larger geotextile circumference will dissipate a larger amount of energy.
Energy dissipation by the sand in the container
Calculations in [5] reveal that the fall energy is too great to be fully dissipated by
strain in the geotextile alone. Therefore, the component
E
fill
has to contribute a signifi-
cant level of energy dissipation. The magnitude of this component is a function of the
dimensions of the geotextile container and the properties of the fill material. Accord-
ing to [17] the following approximate relationship applies for frictional fill material:
)
(6.7)
′
Ah
E
A
(
⋅
A
fill
σ
i
s
s
i
s
where:
fill
=
energy dissipated by the fill material per unit of length [kJ/m];
h
=
height of the container when dumped [m];
