Geoscience Reference
In-Depth Information
Permeability of geotextiles
The permeability of geotextiles in general, and thus also of geotextile-encapsulated
sand elements, has to be great enough to prevent excessive pore pressures from
developing. A safe assumption is that the permeability of the geotextile must be
at least 10 times that of the permeability of the fill material it is filtering. Since
geotextile permeability is difficult to establish, it can also be proposed that there
must be a minimum water pressure differential across the geotextile. For the case
of laminar flow, the hydraulic conductivity of the fill material is described by
Darcy's Law:
(A.1)
qki
s
k
⋅
where:
q
=
specific discharge (
=
Q/A
g
) [m/s];
s
=
hydraulic conductivity of the fill material [m/s];
i
=
hydraulic gradient in the fill material [
−
].
Table A.1 lists typical hydraulic conductivity values for various granular fill
materials.
The flow through a geotextile with sand on one or both sides is usually laminar
since the flow velocity through the geotextile is controlled by the adjacent sand and so
Darcy's Law, based on laminar water flows, can be used in determining the permeability
Table A.1
Hydraulic conductivity of various fill materials [24].
D
50
[m]
k
s
[m/s]
Type of internal
water movement
Material
Clay
Laminar
<
2.10
−
6
10
−
10
-10
−
8
Silt
Laminar
2.10
−
6
-63.10
−
6
10
−
8
-10
−
6
Sand
Laminar
63.10
−
6
-2.10
−
3
10
−
6
-10
−
3
Gravel
Turbulent
2.10
−
3
-63.10
−
3
10
−
3
-10
−
1
Armourstone
63.10
−
3
-0.4
10
−
1
-5.10
−
1
Turbulent
Armourstone (coarse)
0.4-1
5.10
−
1
-1
Turbulent
