Geosynthetics February/March 2024 - 40

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T
By George R. Koerner
New test method for controlling
the manufactured geometry
of geosynthetics
he Geosynthetic Institute (GSI) has a new test method for determining bow and
skew of geosynthetics. This method was created to give installers and product
users a way to quantify the geometric quality control of goods they have purchased.
Geosynthetics are ever increasingly integrated into transportation, geotechnical and
environmental projects where they need to be joined or connected to other components.
If the geometry is not consistent and in compliance with the physical dimensions of the
specification, seams or connections will be difficult or impossible to create. This has led
to all sorts of problems with load transfer, drainage, wrinkles and even leakage.
GRI Test Method GS-34, Standard Test Method for Determining Bow and Skew of a
George R. Koerner, Ph.D.,
P.E., CQA, is the director of
the Geosynthetic Institute
in Folsom, Pa.
geosynthetic was announced on November 1, 2023. This test method is intended to determine
conformance of a geosynthetic to bow
and skew, which are geometric concerns of
manufactured materials. When weft or crossmachine
elements are even at two edges
but arched across the middle, the defect is
known as " bow. " Bowing is a condition in
many geosynthetics where filling yarns or
cross-machine elements are displaced from
a line perpendicular to the selvages and lie
in an arc across the width of the material.
Bowing appears as rows of courses forming
a bow-shaped curvature along the geosynthetic
width, as shown in Figures 1a and
1b, where 1a is a photograph of a uniaxial
geogrid and 1b is a schematic diagram of the
property being measured.
In this determination, a full width geoFIGURE
1A (TOP) Photograph of uniaxial geogrid
FIGURE 1B (BOTTOM) Schematic diagram of
the measurement of " bow "
synthetic test specimen is placed on a flat
surface. A straight edge is then set against
the cross-machine rib or yarn touching both ends simultaneously. The bow is the measurement
of length at the point where the transverse rib or yarn deviates farthest from
the straight edge. One should measure the greatest distance between the perpendicular
line and the yarn, stripe or dominant line at any point across the width of the material.
The process/procedure should be repeated at least three times in places along the length
of the material and then the maximum bow should be reported, along with the location
of the occurrence. If this defect is not resolved, it may cause cutting, sewing/seaming
and connection problems. It may also create serious problems during production like
telescoping or wrinkling. There may also be an issue with residual bowing when the

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Geosynthetics February/March 2024

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