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Geotechnical News •March 2015
GEOSYNTHETICS
Standard No.13, Embankment Dams,
Chapter 5: Protective Filters. It too
offered a commentary on the use of
geotextiles. In many aspects the three
publications share a similar perspec-
tive.
The USSD (2011) White Paper on
Materials for Embankment Dams
provides an outline of important points
that need to be recognised and under-
stood when selecting materials for use
in embankment dams and, in Chapter
7, addresses geosynthetic materials.
Section 7.6 reports on geotextiles as
filters in fill dams, giving consider-
ation to:
• possible applications of geotextiles
as filters in earth dams
• principles of filtration
• differences between geotextile
filters and granular filters
• opening sizes of geotextiles
• filter design criteria for geotextiles
• geotextiles as possible shear sur-
faces
• consolidation and seismic activity
It relies predominantly on the ICOLD
Bulletin 55 of 1986, and appears
to offer limited additional insight.
Importantly, care is urged to ensure
“case histories of satisfactory perfor-
mance of geotextiles in non-critical
applications are not used to justify
uses in critical applications. For
example, successful use of geotextiles
at interfaces where hydraulic stresses
are low or the interface may have been
stable without the geotextile do not
demonstrate suitability for interfaces
subjected to severe flow. Generally,
the performance of the geotextile
cannot be monitored in situ directly
and evidence of deterioration may not
be visible until considerable damage
has occurred. Considerable caution is
required in the design of transitions
that are subject to continuous seep-
age.”
The FEMA (2011) publication
represents “an effort to collect and
disseminate current information and
experience having a technical consen-
sus”. Chapter 3 addresses additional
applications, with Section 3.3 report-
ing on geotextiles in embankment
dams. It includes the following state-
ment explaining current practice for
using geotextiles in U.S. dams:
Table 1. Geotextiles as filters in embankment dams (after Timblin, 1988)
Filter Location
Purpose of Filter
Type of Flow
Significance of Failure Access for Repair
A. Downstream slope
protection.
Control of erosion by
rainfall.
Occasional surface
flow.
Noncritical.
Easy.
B. Downstream
surface drains.
Removal or surface
seepage.
Continuous local
seepage.
Noncritical. Local wet
areas may reappear.
Easy.
C. Upstream slope
protection.
Control of erosion by
wave action and by
outward flow during
drawdown.
Cyclic flow during
wave action. Small
flow during
drawdown.
Usually
noncatastrophic.
Possible.
D. Temporary internal
drainage.
Dissipation of excess
pore pressure during
construction of wet
fills.
Temporary flow,
limited quantity. some
migration of fines
allowable if drains not
blocked.
Noncatastrophic.
Failure may lead to
instability during
construction or delays.
None.
E. Upstream internal
fill boundary.
Prevention of unac-
ceptable migration
of fines in upstream
direction.
Transient and small
flows during
drawdown.
Noncatastrophic. Only
significant if migration
is large and
continuous.
None.
F. Downstream
internal interface-no
continuous flow from
reservoir.
Prevention of
unacceptable
migration of fines.
Flow only due to
infiltration of rainfall.
Limited and non-
catastrophic.
May be possible to
excavate with
reservoir drawn down
for safety.
G. Downstream
internal interface-no
continous flow from
reservoir.
Prevention of inter-
nal erosion including
effects of concentrated
flow in cracks, etc.
Continuous flow from
reservoir, potentially
large and increasing.
Potentially
catastrophic and rapid.
General seepage may
involve slow
deterioration.
Generaly none. Down-
stream weight block/
inverted filter may be
removed and repair
accomplished only
with reservoir drawn
down for safety.
