Geosynthetics October/November 2020 - 27

Case Study

A geosynthetic
wrap-face vegetated
wall system
For highway embankment construction
By Stanley M. Miller and Drew Loizeaux

A

recent creek enhancement project to facilitate the passage of bull trout in Pend Oreille County of northeastern
Washington state required removal of a 6-foot (1.8-m) diameter
concrete culvert (Figure 2 on page 28), realignment of a welltraveled county road and a new 58-foot (17.7-m) span bridge.
The new alignment would cross a low-lying area adjacent to the
Pend Oreille River, which is subject to seasonal flooding in late
spring due to water releases from an upstream dam. Limited
right-of-way access provided a relatively narrow footprint for
the planned earth-fill embankment approaches needed for
the new bridge. Thus, they would require steep side slopes or
near-vertical retaining wall structures, such as a concrete-panel
mechanically stabilized earth (MSE).
Due to geotechnical concerns over differential settlements
expected with soft foundation soils, and because project
stakeholders and the Pend Oreille County Public Works
Department preferred a vegetated-face alternative for the
embankment slopes, a geosynthetic wrap-face vegetated
(GWFV) wall system was selected (Figure 1), known as
PYRAWALL. This reinforced-soil system uses 1-foot (0.3m) high uniform wrap lifts and relies on three components
(Miller 2017): 1) a polypropylene high-performance turf
reinforcement mat (HPTRM) to form the wrap-face lifts and
secondary soil reinforcement; 2) internal fiber-composite
braces that hold up the face and allow filling and compaction
of the soil lifts; and 3) geogrid layers that extend back into the
embankment for primary soil reinforcement.

PROJECT HIGHLIGHTS
A GEOSYNTHETIC WRAP-FACE
VEGETATED WALL SYSTEM
OWNER

Pend Oreille County Public Works
(Newport, Wash.)
LOCATION

Indian Creek Bridge on LeClerc
Road South, Pend Oreille County
GENERAL CONTRACTOR

N.A. Degerstrom Inc.
(Spokane, Wash.)
DESIGN ENGINEER

Nicholls Kovich Engineering, PLLC;
and STRATA Inc. (Spokane, Wash.)
GEOSYNTHETICS PRODUCT

PYRAWALL
GEOSYNTHETICS MANUFACTURER

Propex Operating Company LLC

Stanley M. Miller, Ph.D., P.E., is professor
emeritus in the Department of Civil
Engineering at the University of Idaho and a
consulting engineer based in Moscow, Idaho.
Drew Loizeaux, M.S., P.E., is an engineering
specialist in Propex GeoSolutions for
Propex Operating Company LLC, in
Chattanooga, Tenn.
All figures courtesy of the authors.

www.GeosyntheticsMagazine.com

1020GS_p26-35.indd 27

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9/22/20 1:18 AM


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Geosynthetics October/November 2020

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

Geosynthetics October/November 2020 - Cover1
Geosynthetics October/November 2020 - Cover2
Geosynthetics October/November 2020 - 1
Geosynthetics October/November 2020 - 2
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Geosynthetics October/November 2020 - Cover3
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Geosynthetics October/November 2020 - Geosynthetics Conf. Brochure 1
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