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Geotechnical News •March 2015
GEOSYNTHETICS
Jonathan Fannin, Editor
Professor of Civil Engineering, University of British Columbia
Geofilters Part 2
Jonathan Fannin & Kelvin Legge
In the Geofilters Part 1 article that was
published in the GN: December 2014
issue, I sought to contrast the path-of-
discovery through which practice in
granular filters has evolved, with that
for the origins of practice in specifying
a geotextile filter. The intent was to
discriminate between what we really
know, and what we merely believed,
about the merits of using a geotextile
filter.
This companion Geofilters: Part 2 now
reviews select guidance that is cur-
rently used for granular filters, as well
as that for geotextile filters, placing
emphasis on applications in embank-
ment dam engineering and matters
pertaining to base soil-filter layer
compatibility. Thereafter, consider-
ation is given to the content of a new
draft bulletin from the South African
National Committee on Large Dams
(SANCOLD) – a substantial work-in-
progress to revise and update the 1985
ICOLD Bulletin 55 on “Geotextile Fil-
ters in Dams”- for which I am grateful
to my co-author Kelvin Legge. But
first, let us commence with some very
general reflections on dam engineer-
ing, both past and present.
Dam engineering: 3500 BC to
the present day
Throughout the ages the lives of
people and water have been inex-
tricably linked (Fig. 1). For sev-
eral thousand years, societies have
diverted and dammed rivers to meet
their increasing water needs, with the
earliest evidence of canal irrigation in
Neolithic civilisations dating back to
c. 6500 BC, in the southern regions of
modern-day Iraq (Viollet, 2007). On a
planet that is mostly covered in water,
but where less than 2.5% of it is fresh-
water, the ability of societies to regu-
late and manipulate the water that is
available to them has not only proven
key to their progress and development,
but to their very survival. Writing on
the subject of early dams, Fahlbusch
(2009) notes what is often regarded
as the oldest known dam in the world,
at Jawa in modern-day Jordan, which
dates to c. 3500BC, comprised a
basalt stone shell with a core of “clay,
ash and soil that had been tamped”.
The Sadd el Kafara dam in modern-
day Egypt dates to c. 2650 BC, and
comprised a core of “silty sand and
gravel” that was supported on either
side by layers of rockfill and revet-
ment stone, yielding a structure that
was approximately 110m long and 14
m high. “The examples at Jawa and
Sadd el Kafara show the Bronze Age
engineers were able to construct high,
Jonathan Fannin
Kelvin Legge
