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Geotechnical News • September 2016
GEOSYNTHETICS
soil. The opening size of the geotextile
is typically reported with reference to
one of three standardized index test
methods of sieve analysis, for which
laboratory comparisons yield a similar
but not identical value of characteristic
pore size opening. Accordingly, there
are modest differences between the
various empirical criteria that are used
for soil retention.
Filtration compatibility is evaluated
from permeameter testing. Since the
first laboratory studies reported in
1972, the configuration of test equip-
ment has evolved to include develop-
ment of standardized test methods
for rigid-wall permeameter testing
of geotextile compatibility with a
relatively coarse-grained base soil, and
flexible-wall permeameter testing of
compatibility with fine-grained soil.
In the last 20 years, the state-of-the-art
has advanced to include refinements
to equipment and procedures that
have enabled compatibility testing
in unidirectional and reversing flow
with a mechanics-based interpretation
of the results which accounts for the
combined influence of hydraulic gradi-
ent and effective stress. The findings
of these systematic laboratory studies
not only provide confidence in the use
of empirical design rules, but have
also provided a means to quantify the
inherent conservatism of the empiri-
cal criteria that are used in routine
practice. In more critical or severe
applications, the standardized tests
also provide a means to evaluate soil-
geotextile compatibility in advance
of construction. In such projects, the
state-of-practice is first to identify a
candidate geotextile on the basis of the
reported values for its strength, open-
ing size and permittivity from index
testing, and then to evaluate its suit-
ability for the proposed construction
application from performance testing
of a sample of the base soil in combi-
nation with that candidate geotextile
filter.
Acknowledgements
The preparation of this article has
drawn upon a number of published
and unpublished sources. The permis-
sion of BC Hydro Dam Safety, most
notably Stephen Rigbey and Kay Ahl-
field, to report on information relevant
to the selection and specification of a
geotextile filter at the Alouette Dam is
gratefully appreciated. The specifica-
tion of the geotextile was developed
in close collaboration with the Project
Engineer (Stephen Garner, BC Hydro,
now retired), with whom it was a
pleasure to work, and whose experi-
ence was instrumental to the success
of the project.
References
ASTM D5101. Standard Test Method
for measuring the soil-geotextile
clogging potential by Gradient
Ratio.
ASTM International
, USA.
ASTM D5567. Standard Test Method
for Hydraulic Conductivity Ratio
(HCR) Testing of Soil/Geotextile
Systems.
ASTM International
,
USA.
B.C. Hydro (personal communication)
on the approach to project design
and performance monitoring.
Brown, P.T. and Nielson, N.M. (1992).
Dams + debris = danger.
Proc.
Dam Safety ’92
. Can. Dam Asso-
ciation, 11p.
Carpenter, E.E. (1927). The Water
Power Developments of the
Alouette-Stave-Ruskin Group
of the British Columbia Electric
Railway Company, Limited.
The
Engineering Journal,
Engineering
Institute of Canda, Montreal, QB,
p.17-39.
Fannin, R.J. (1990). Alouette Dam
Spillway Rehabilitation, B.C.,
Phase I report: Feasibility study,
July 1990.
Fannin, R.J. (1991). Alouette Dam
Spillway Rehabilitation, B.C.,
Phase II report: Preliminary
Design, Feb. 1991.
Hartford, D.N.D. and Lou, J.K.
(1994). Consequence based safety
evaluation of an earth dam for
floods and earthquakes.
Proc. Dam
Safety ’94
, Can. Dam Association,
22p.
Williams, N.D. and Abouzakhm, M.A.
(1989). Evaluation of geotextile/
soil filtration characteristics using
the Hydraulic Conductivity Ratio
analysis
. Geotextiles and Geomem-
branes,
8:1-26.
The Vancouver Geotechnical Society
and the
Canadian Geotechnical Society
69th Canadian GeoteChniCal ConferenCe
Topics and specialty sessions of local and national relevance to geotechnical and geo-environmental engineering
October 2 to 5, 2016 • Westin Bayshore Hotel • Vancouver British Columbia
