Geosynthetics June/July 2019 - 22

Geogrid reinforced soil structures reach new heights

PROJECT HIGHLIGHTS
U.S. ROUTE 460
CONNECTOR RSS
OWNER

Virginia DOT
LOCATION

Grundy, Va.
GENERAL CONTRACTOR

Bizzack Construction LLC
DESIGN ENGINEER

The Collin Group
FASCIA SYSTEM

Welded wire form with biaxial
geogrid and stone facing
GEOSYNTHETIC PRODUCTS

Maccaferri Uniaxial geogrids
Nonwoven geotextile
GEOSYNTHETIC MANUFACTURER

Maccaferri Inc.

FIGURE 10 U.S. Route 460 RSS facing detail

Geosynthetics | June July 2019

U.S. Route 460 Connector-Phase II:
Reinforced soil slope
A 6.2-mile (10-km) roadway alignment
of U.S. Route 460 Connector-Phase II
project is creating a new stretch of a
four-lane divided highway that primarily serves as a connector to the future
Coalfields Expressway from the community of Breaks, Va. The new roadway
alignment traverses mountainous and
densely wooded terrain with a wide range
of geologic formations that predominantly
consist of sandstone, shale and coal.
As part of this design-build project,
welded wire-faced RSS ranging from
0.75H:1V to 1.5H:1V, with a maximum
height of 80 feet (24 m), and extending a
total length of 550 feet (168 m) was constructed along the project alignment to
gain adequate roadway width. Alternately,
very long and steep downslope embankments could have been constructed but
would have significantly increased the
cost, lengthened the construction duration and affected the forest. The RSS was
founded on bedrock below or high enough
above the coal seam and stretched through
cut and fill areas. The RSS was constructed with multiple layers of primary
reinforcement using uniaxial polyester
geogrids vertically spaced at 18 inches (46
cm) and biaxial polypropylene geogrids
wrapped in the fascia and extended into

the reinforced fill as secondary reinforcements. Galvanized welded wire forms
were used in the facing to retain the fascia
stones. Figure 10 shows the welded wire
form facing detail used in this RSS project.
Computer programs ReSSA 3.0 and
Slide 6.0 were used to analyze the internal, compound and global stabilities of
the proposed RSS. The design analyses
included both circular and wedge failure
modes for the representative RSS cross
sections. The analysis outcomes from
both programs showed similar factors of
safety and failure surfaces.
Initially, the RSS was designed using
soil parameters recommended in the geotechnical report. However, the sieve analysis report of on-site excavated and crushed
material showed higher than desirable
percentage of material retained on a 4-inch
(10-cm) sieve. This gradation resulted in
an unknown installation damage reduction factor, and on-site installation damage assessment was required. This stood
to delay the project several weeks, as the
construction of RSS was on a critical path.
To avoid construction delays, the contractor was instructed to start constructing the
RSS, provided the primary reinforcement
was placed at 9 inches (23 cm) vertical
spacing instead of 18 inches (46 cm) until
the installation damage reduction factors
were obtained. The on-site installation

Geosynthetics June/July 2019

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