Geosynthetics April/May 2020 - 27

the dimensional integrity by encasing and protecting the yarns from
construction-induced damage, environmental exposure and dimensional
stability while the polyester yarns are
the load-carrying elements.
* Connection recess embedded in the
facing panel composed of smoothsurface, blow-molded, polyolefin,
omega-shaped sleeve. When the geosynthetic strip is threaded through
the sleeve, the connection recess
provides a fully synthetic integral
mechanical connection.
The polymeric strip used for the
structure has a nominal strength of 11.24
kip (50 kN) and a nominal width of 2
inches (50 mm). Quality control in production of the strip will yield a 100% certainty that the values tested for the strip
are higher than the nominal value used
for design. Polymeric properties of polyester yarns follow the requirements of the
American Association of State Highway
and Transportation Officials (AASHTO)
for molecular weight and carboxyl end
groups. The allowable design strength of
the geosynthetic strip is based on material-specific testing used to derive reduction factors (AASHTO-NTPEP 2017).
The long-term performance of geosynthetic reinforcement is influenced by
factors such as time, temperature, load,
installation conditions and environmental exposure. These factors, specific to
polymer type and product, directly affect
long-term performance and durability,
and must be determined and considered
in design when using geosynthetics.

Research
Andrawes et al. (1978) originally defined
the differences between the relative
extensibility of the reinforcement inclusions. Inextensible inclusions are those
that "have rupture strains which are less
than the maximum tensile strains in the

soil without inclusions, under the same
operational conditions," and "extensible
inclusions are those that have rupture
strains larger than the maximum tensile
strains in the soil without inclusions,
under the same operational conditions."
This has been the basis for the separation
of types of reinforcements in AASHTO.
It was determined that the pullout
resistance of extensible and inextensible inclusions is mobilized differently
(Segrestin and Bastick 1996). However,
when compared to inextensible, ribbed
steel strips in pullout tests, 2-inch (50mm) polyester strips mobilized the dilatational frictional behavior in an analogous
manner to ribbed steel strips (Lozano
and Sankey 2013). Still, as reported by
Anderson et al. (2012), geosynthetic strips
develop frictional resistance along the
length of reinforcement quite differently
from inextensible steel strip reinforcements, as evidenced by the lack of trailing
end displacement on the polyester strip.
MSE walls have been constructed with
instrumentation to further understand
the tensile load and pullout resistance in
the reinforcement layers. Although geosynthetic strip reinforcements have been
in use worldwide for at least four decades,
there is limited instrumented structure
data. One of the reasons for this is the
complexity in attaching the right type
of instrumentation directly to polyester
fibers in the geosynthetic strip. Due to the
two-part composition of a geosynthetic,
it has proven extremely difficult to install
strain gauges that can withstand the rigors of earth-moving construction without
substantially altering the reinforcement
geometry and stiffness properties. As
such, out of the hundreds of structures
constructed, only two relevant case histories are available in the literature with
sufficient data in the instrumentation:
the St. Remy wall and the Christiana wall.
The structure located in St. Remy,
France, was designed and supplied by

Due to the two-part
composition of a
geosynthetic, it has
proven extremely
difficult to install
strain gauges that can
withstand the rigors
of earth-moving
construction without
substantially altering
the reinforcement
geometry and
stiffness properties.

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Geosynthetics April/May 2020

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