Geoscience Reference
In-Depth Information
Stability subject to current over the structure
In the case of well-designed bank protection there is no current over the structure.
Required geotextile tensile strength
The required geotextile tensile strength when dumping the geotextile bags can be
determined using formula (3.3):
⋅
⎛
⎜
⎞
⎟
DV
bS
J
C
ρρ
−
T
2
n
w
⎛
⎝
⎞
⎠
ρ
g
=⋅
⋅
⋅
⋅
ρ
d
w
The geotextile bags are produced from woven polypropylene with a tensile
strength of 120 kN/m at a corresponding strain of 14%. The tensile stiffness modulus
J
of the geotextile can be determined using formula (2.2):
T
120
014
857 kN
/
m
J
T
==
m
=
ε
m
The tensile load in the geotextile can now be determined by (
J
in formula 3.3 has
to be presented in N/m):
3
0.75 1.875 857 10
⋅
⋅
1908
−
1000
⎛
⎞
T
=⋅
2
⋅
⋅
⋅
1908 9.81
⋅
⎜
⎟
⎝
⎠
2.5 6.5
⋅
1
1000
T
=
50 kN/m
This is the theoretically calculated tensile load that any seam in the geotextile bag
must be able to resist. If it is assumed that the seams achieve a strength of 70% of the
strength of the geotextile, the required tensile strength of the geotextile is then:
T
50
07
am
72
kN
/
m
T
se
T
=
sea
=
=
T
geotextile
07
7
0
1.0 may be applied since the formula for determining
the required tensile strength already has a number of safe assumptions:
An overall safety factor
γ
=
T
120
72
omplies
167
.
67
⇒
⇒
c
=
=
T
T
geotextile
Sand movement within the geotextile bag
The water flow is less than or equal to 1.5 m/s, so there is little likelihood of sand
movement within the geotextile bag.