Geosynthetics October/November 2020 - 30

A geosynthetic wrap-face vegetated wall system

394), and those analysis results also met
accepted design criteria.
A generalized schematic showing various components of the GWFV
wall designed for the bridge-approach
embankments is presented in Figure 3.

Overview of GWFV
wall system

FIGURE 3 Schematic of GWFV wall for
highest section of the west bridge-approach
embankment (maximum length of geogrids
is 11 feet [3.4 m]).

30

then 2 feet (0.6 m) elsewhere. Wall calculations showed the minimum required
long-term design strength (LTDS) to be
approximately 1,300 pounds/foot (19
kN/m). However, subsequent global stability analysis for large-scale rotational
failure paths (Abramson et al. 2002)
indicated that stronger geogrid layers
would be needed in the lower portion
of the embankment to provide adequate
resistance to potential "compound" failure paths that could pass through the
reinforced zone. The final design specified that the lower geogrids have a minimum required LTDS=3,600 pounds/foot
(52.5 kN/m) and the remaining geogrids
have a minimum required LTDS=1,800
pounds/foot (26.2 kN/m).
The above analysis results were based
on static-loading conditions. Stability
calculations for dynamic (seismic) conditions also were conducted by pseudostatic methods, using a locally estimated
horizontal seismic coefficient of kh=0.09
(refer to Abramson et al. 2002, p. 354 and

The rolled HPTRM used for the face
wraps is 8.5-feet (2.6-m) wide by 120-feet
(36.5-m) long. As illustrated in Figures 1
and 3, this width provides a typical wrap
layer with 4 feet (1.2 m) along the bottom,
a 1-foot (0.3-m) near-vertical face, and 3.5
feet (1.1 m) folded back over the soil infill
lift. The geosynthetic provides excellent
erosion protection as vegetation seeded in
the infill soil ("internal seeding") emerges
and becomes established. The open weave
of the fabric also is conducive to vegetation being established by hydroseeding
("external seeding") after the wrap-face
structure has been completed.
The unique lofted, three-dimensional
feature of this HPTRM allows for the
insertion (weaving) of bracing-bar components, which stand up the 1-foot (0.3m) high section of the fabric, forming
a face against which infill soil is placed
and compacted. These bracing bars are
fabricated using a high-strength fibercomposite material consisting of nylon
and fiberglass.
Primary geogrid reinforcement is
added to the system by inserting ("sandwiching") the geogrids between successive wrap lifts, applying a thin soil layer to
inhibit any fabric-to-fabric contact. Wood
stakes or metal pins can be used to stretch
both the HPTRM and the geogrid taut
and hold them in place while soil backfilling occurs. A construction photograph
presented in the next section (Figure 5
on page 32) shows both types of fabric
and a typical granular soil used to coat the
inserted geogrids.

Geosynthetics | October November 2020

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Geosynthetics October/November 2020

Table of Contents for the Digital Edition of Geosynthetics October/November 2020
