Geoscience Reference
In-Depth Information
Figure A.2
Clogging mechanism.
With clogging, (see Figure A.2) the geotextile pores fill up because fine particles
of the fill material force their way into the geotextile structure and block the pore
channels. This has also been called 'mineral clogging' and occurs mostly in nonwoven
geotextiles. Despite clogging reducing the permeability of geotextiles by some 50%,
studies have shown that the resulting permeability of nonwoven geotextiles is still
greater than that of the fill material. It is proposed [22, paragraph 4.5.3.1] that clog-
ging will not occur if:
For
C
u
>
3:
O
95
/
D
b
15
>
3;
For
C
u
3: criterion for internal stability of fill should be satisfied and/or a geo-
textile with maximum opening size from the soil-tightness criteria should be
specified.
<
Blocking can lead to a reduction of the permittivity (and thus of the permeability
too) by a factor of 5. Clogging can cause even a higher reduction to occur [39].
CALCULATION EXAMPLE
Situation
Geotextile containers have been selected as the filled elements for the construction
of a dam. The containers will be filled with sand (
k
s
=
10
−4
m/s,
D
90
=
0.2 mm and
D
15
0.1 mm). In the vertical plane the container has a width of 7 m and height of 2 m.
The water level is on one side of the container 0.5 m higher than on the other side.
The supplier prescribes a geotextile that is characterized by the following proper-
ties:
O
90
=
0.6 mm and a velocity index of 0.004 m/s determined in accordance with
EN ISO 11058. Thus, using formula A.3
=
Ψ
=
0.08 s
−1
).
