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Geotechnical News • June 2014
www.geotechnicalnews.com
GEOSYNTHETICS
Terzaghi’s path-of-discovery toward
the design of granular filters (Fannin,
2008). I grew to appreciate the legacy
of his systematic experimentation as a
university academic, his challenging
assignments as a specialist consultant,
his life-long respect for the influence
of minor geologic features, his rigor-
ous approach to the interpretation of
evidence, and his unstinting commit-
ment to performance monitoring. And
with this appreciation, I too sought
out every opportunity to ensure that I
had a proper understanding of events
related to the nature and origin of
geotechnical filter design, for which I
acknowledge, with gratitude, con-
versations with several individuals
including Terzaghi’s co-author on the
textbook “Soil Mechanics in Engineer-
ing Practice”, Ralph Peck, at the 57
th
Canadian Geotechnical Conference
(Fig. 3).
I also have no doubt that Terzaghi
brought the same unstinting commit-
ment to excellence when he oversaw
the design and installation of a PVC
membrane liner during construc-
tion of the 55 m high Mission Dam,
British Columbia, Canada that was
subsequently renamed the Terzaghi
Dam, in 1965. As might be expected,
the problem was anything but simple.
Following early exploratory work in
1955, placement of zoned embank-
ment materials commenced in 1957
and continued through to 1960
(Terzaghi and Lacroix, 1964). The
dam is founded on a discontinuous
clay stratum that is underlain by sand
and gravel, and overlain by alluvial
and river channel deposits. The clay
stratum itself represents the down-
stream portion of glacial lake deposits
arising from the last stage of reces-
sion of the Pleistocene ice sheet: the
boundary between it and the overlying
coarse-grained sediments was found
to be clear but very uneven, likely as a
result of geological processes follow-
ing retreat of the valley ice. Settlement
of the embankment occurred during
construction, including differential
settlements of up to 3 m. The zoned
embankment dam has a sloped till-
core that is covered by an upstream
blanket of plastic clay, about 2.5 m
thick. The performance of the dam is
contingent on the clay blanket remain-
ing intact, without any cracks or
fissures arising from the influence of
differential settlement. Concern for the
adverse impact of any cracking led to
the decision to cover select portions of
the clay blanket with a plastic mem-
brane. The choice of plastic material
Figure 2. Reading through professional correspondence in the Terzaghi
Library at the Norwegian Geotechnical Institute.
Figure 3. Consultation with Ralph Peck on the origins of the filter design
criteria appearing the “Soil mechanics in engineering practice” co-authored
with Karl Terzaghi.