Environmental Engineering Reference
In-Depth Information
Figure 9.34.
Transmissivity versus applied normal stress for various needle punched non woven geot-
extiles (Koerner, 1986, reproduced with permission of Pearson Education).
The second is achieved through having sufficient transmitting (or permeability) across
the plane of the geotextile, but in addition, there is a requirement to control the likelihood
of clogging of the geotextile.
9.7.2.2
Filtering requirement
There are many different filter design criteria for geotextiles. Summaries are given in
Bertacchi and Cazzuffi (1985), ICOLD (1986) and Christopher et al. (1993). Critical
reviews are given in Giroud (1996) and Heerten (1993).
Table 9.13
summarizes some of the methods.
Palmeira and Fannin (2002) give a more recent review but they do not recommend a
particular method.
The authors are not in a position to give clear guidance on what criteria should be used.
In principle, we would favour a method which is based on the D
85B
, (or D
90B
, D
95B
) of the
base soil, rather than D
50B
, because in conventional filters, Sherard et al. (1984a) and
Foster (1999) have demonstrated D
50B
is a poor guide to filter characteristics. This would
favour the use of Loudiere et al. (1982) (upon which ICOLD 1986, also seem to have
relied), and Heerten (1993). Giroud (1982, 1996) (along with Loudiere et al., 1982)
specifically discuss the application to dams.
The authors' advice would be to try these three methods and, if necessary, seek guid-
ance from the more recent literature and/or manufactures of geotextiles.
