Geosynthetics February/March 2022 - 8

Q &
RESISTING CLOGGING
WITH FILTRATION
THE GEOSYNTHETIC
INSTITUTE ANSWERS
YOUR QUESTIONS
gmatechline@ifai.com
View past questions and answers at
https://geosynthetics.ifai.com/programs/
gma-techline. Email gmatechline@
ifai.com anytime for fast, free, direct
technical answers.
Q: I have a question about the Filter Criteria
in the Federal Highway Administration
(FHWA) Filter Design procedure, specifically
the clogging resistance equation 2-10. This
seems to require a particularly large pore size;
for example, if the D15 of the soil was for 70
microns, the minimum O95 of the fabric would
be more than 200 microns, something we
rarely see in a nonwoven geotextile. Wouldn't
the soil filter that forms upstream of the fabric
in steady state flow resist clogging even with
a smaller pore size?
A: Thank you for your GMA Techline question.
As you know, filter design is a balancing act
between piping and clogging. The FHWA is
now using open geotextile filters and dealing
with any fines that may flush through the
system downstream. I have referenced a
PowerPoint presentation from Petrasic (2018)
that ushered in this design mentality. There
is much discussion about active and passive
fines management systems in the United
States now. The formation of an upstream
soil filter cake in advance of the geotextile is
critical for success of such designs. Many are
suggesting that the geotextile merely acts as
a catalyst to initiate filter cake formation.
Petrasic, K. (2018). " Geotextile separation to prevent
migration of subgrade soil into unbound aggregate
subbase. " Proc., 30th ASCE Central PA Technical Conf.,
Hershey, Pa.
A
GMA TECHLINE
MODERATED BY
George R. Koerner
SEWN VERSUS WELDED SEAMS
FOR GEOSYNTHETIC CLAY LINERS
Q: On your website list of sample questions
and answers (https://geosynthetics.ifai.com/
programs/gma-techline), a question is asked
about a recommendation for sewn versus
welded seams for geotextiles. Bob Koerner
answered this question by stating that you
have done a study for joining geosynthetic
clay liner (GCL) overlap seams via eight
methods. Can you share that study with me?
A: I think the references you are referring
to are as follows:
Koerner, R. M., and Koerner, G. R. (2005). " Insitu
separation of GCL panels beneath exposed
geomembranes. " GRI White Paper #5, Geosynthetic
Institute, Folsom, Pa.
Koerner, G. R., and Koerner, R. M. (2015). " Destructive
and nondestructive testing of GCL panel seams. " Proc.,
Geosynthetics Conf. 2015, Industrial Fabrics Association
International, Roseville, Minn.
These publications are informative, but they
spawned the following:
GRI GCL6: Practice for Field Seaming of Overlapped
Geosynthetic Clay Liners (GCLs)
GRI GCL7: Test Method for Determining the Tensile
Shear Seam Strength of Geosynthetic Clay Liners (GCLs)
GRI GCL8: Test Method for In-Situ Tensile Strength
Verification of Geosynthetic Clay Liner (GCL) Seams
These test methods and practices are practical
and ready for field quality assurance/quality
control (QA/QC).
8
Geosynthetics | February March 2022
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Geosynthetics February/March 2022

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