52
Geotechnical News •March 2015
GEOSYNTHETICS
• the importance of competent filters
in avoiding dam failures
• granular materials as filters in dams
• geotextile uses and applications
• principles of geotextile filtration
• differences between geotextile
filter materials and granular filter
materials
• filter design criteria for geotextiles
• the effects of time and permeating
fluids on service life
• composite (granular and geotextile)
filters
• quality assurance (materials and
construction)
• durability of geotextiles
In giving recognition to the impor-
tance of competent filters, the preva-
lence of failures arising from internal
erosion of the body of the dam is
noted. What is perhaps the most novel
intended contribution of the current
version (2.0) of the SANCOLD draft
revision is the concept of a com-
posite filter, where proven compat-
ibility allows for use of a geotextile
as an adjunct to a granular filter, for
example in a chimney drain where the
application is primarily intended to
protect against contamination of the
filter by core material during con-
struction, as well as protect against
unacceptable internal erosion during
first filling.
The compilation of experience, both
in South Africa and elsewhere in the
technical literature, pertaining to dam
engineering and related construc-
tion applications, is leading to the
proposition that “geotextiles can thus
be used in non-critical applications
as primary filters and can be used as
adjuncts to granular filters in critical
applications to form a composite filter
material”. As noted at the beginning
of this Geofilters: Part 2 article, the
SANCOLD activity is a substantial
work-in-progress to revise and update
the 1985 ICOLD Bulletin 55. The
approach advances beyond that of
the USBR (2011) and FEMA (2011)
publications, and is herefore deserv-
ing of considered deliberation. It is
the changing nature of water quality
and availability of ideal granular filter
materials, informed by laboratory and
field investigations, which has led to
advocating the use of composite gran-
ular and geotextile filters in critical
applications in dam engineering. The
approach is proposed so as to embrace
the benefits offered by geotextile and
by granular filters under suboptimal
conditions, while recognising that
limitations of one material type may
be complemented by the relative
advantages of the other material type.
Accordingly, and in closing on this
Geofilters: Part 2, my co-author
Kelvin Legge would be delighted to
receive correspondence from those
with any experience using composite
geotextile-granular filters in dams,
with a view to compiling case studies
on the subject to inform the SAN-
COLD revisions and updates to the
1985 ICOLD Bulletin 55 on “Geotex-
tile Filters in Dams”.
References
Fahlbusch, H. (2009). Early dams.
Proceedings of the Institute of
Civil Engineers, Engineering His-
tory and Heritage 162, Issue EHI,
pp.13-18.
FEMA (2011). Filters for Embank-
ment dams: Best practices for
design and construction. October
2011.
SANCOLD (2014). Geotextile filters
in dams. SANCOLD revision of
ICOLD Bulletin 55, Draft 2.0 of
September 2014.
USBR (2011). Design Standard No.
13, Embankment Dams, Chapter
5: Protective Filters, DS-13(5)-
9: Phase 4 (Final). United Sates
Bureau of Reclamation, Technical
Service Center, November 2011.
Timblin, L.O. (1988). Geosynthetics
in dam construction, in Chapter of
Advanced Dam Engineering for
Design, Construction and Reha-
bilitation, Ed. R.B. Jansen, Van
Nostrand Reinhold, New hyork,
811 p.
Viollet, P.-L. (2007). Water engineer-
ing in ancient civilizations: 5,000
years of history. International
Association of Hydraulic Engi-
neering and Research (IAHR)
Monograph Series, Madrid, Spain,
322p.
Kelvin Legge
Chief Engineer
Department of Water and
Sanitation
64 Jean Ave., Doringkloof
Centurion 0157
Republic of South Africa
