Geosynthetics October/November 2020 - 28

A geosynthetic wrap-face vegetated wall system

Site conditions

FIGURE 2 Concrete culvert to be removed

Potential Failure Mode

ASD
Calculated 1FS
(Design Criteria)

LRFD
Calculated Value
(Design Criteria)

External: Base Sliding

2.32 (FS ≥ 1.5)

1.64 (2CDR > 1)

External: Overturning
(Eccentricity Limit)

6.28 (FS ≥ 2.0)

0.238 (3e ≤ 0.25)

External: Bearing Capacity

5.73 (FS ≥ 2.0)

1.75 (CDR > 1)

Internal: Geogrid Rupture

For FS = 1.5,
LTDS > 1300 lb/ft (19 kN/m)

X

Global Stability by
Method of Slices

1.50 (FS ≥ 1.5)

X

1FS

is Factor of Safety;

2CDR

is Capacity to Demand Ratio;

3e

is Eccentricity Limit

TABLE 1 Stability analysis results for tallest GWFV wall section (18 feet [5.5 m]).

28

To accommodate the new bridge, realignment of the road would require a west
approach embankment 340-feet (104-m)
long with a maximum height of 18 feet
(5.5 m), and an east approach embankment 210-feet (64-m) long with a maximum height of 13 feet (4 m). Public and
private borrow sources within 3 miles
(4.8 km) of the project site contained
approved granular, structural fill, which
was classified as Well-Graded Gravel with
Silt and Sand (GW-GM, according to the
Unified Soil Classification System), with
less than 8 percent passing the No. 200
sieve. A private borrow source for topsoil
also was located nearby.
Soil borings completed along the
proposed realignment showed mixed
alluvium soil with generally high groundwater levels; i.e., within 8 feet (2.4 m)
of the ground surface. Subsurface soils
included silt, silty sand, silty gravel and
poorly graded sand with silt or gravel,
with some zones (often between 10 and
20 feet [3 and 6 m] below ground surface)
having very low standard penetration test
(SPT) blow counts in the N=2 to 5 range.
Higher blow count materials (N=20 to
50) were encountered at depths from 30
to 50 feet (9.1 to 15.2 m).

Geotechnical considerations
Where the two approach embankments
terminate at the bridge abutments, steel
sheet-pile walls were designed to provide a bulkhead for the embankment fill
and to provide long-term erosion and
scour protection along the creek bank on
either side. In addition, micropile foundations were designed for both bridge
abutments to provide adequate bearing
capacity for the single-span bridge. The
micropiles (hollow-bar, grout-injected
Grade 70 steel) and concrete pile caps were
installed behind the sheet-pile walls on
either side of the creek. Thus, the GWFV

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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
Geosynthetics October/November 2020 - 3
Geosynthetics October/November 2020 - 4
Geosynthetics October/November 2020 - 5
Geosynthetics October/November 2020 - 6
Geosynthetics October/November 2020 - 7
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Geosynthetics October/November 2020 - 16
Geosynthetics October/November 2020 - 17
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Geosynthetics October/November 2020 - 24
Geosynthetics October/November 2020 - 25
Geosynthetics October/November 2020 - 26
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Geosynthetics October/November 2020 - 48
Geosynthetics October/November 2020 - Cover3
Geosynthetics October/November 2020 - Cover4
Geosynthetics October/November 2020 - Geosynthetics Conf. Brochure 1
Geosynthetics October/November 2020 - Geosynthetics Conf. Brochure 2
Geosynthetics October/November 2020 - Geosynthetics Conf. Brochure 3
Geosynthetics October/November 2020 - Geosynthetics Conf. Brochure 4
Geosynthetics October/November 2020 - Geosynthetics Conf. Brochure 5
Geosynthetics October/November 2020 - Geosynthetics Conf. Brochure 6
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Geosynthetics October/November 2020 - Geosynthetics Conf. Brochure 8
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