Geosynthetics April/May 2024 - 19

results and discussions are presented
elsewhere and will not be given herein
(Chang et al. 2022).
GRS design
1. Foundation improvement
Because the GRS embankment is located
on the colluvium with poor engineering
properties, its bearing capacity needed to
be improved. In addition, restraining the
fault zone displacement from the foundation
would achieve a better reinforcement
effect (Chiang et al. 2022). Therefore, the
weak soil under the embankment was
replaced by a GRS foundation. It was
done by removing the underlain weak
shallow colluvium and replacing it with
the GRS foundation.
In Figure 7, ACEGrid® GG150-I
geogrids were arranged in a crisscross
pattern. These geogrids have an ultimate
tensile strength of 10,243.90 lbs/ft (150
kN/m) and are made of high-tenacity,
multifilament polyester yarns. They are
coated with a durable polymer for low
creep behavior, high tensile modulus,
and longevity (ACE Geosynthetics 2024).
Two geogrid layers were laid in the warp
direction with a vertical spacing of 2.0
feet (0.6 m) perpendicular to the highway
direction. Then a layer of geogrid was laid
in the direction of parallel latitude (parallel
to the highway direction) at a space
of 1 foot (0.3 m). Backfill for the GRS
foundation was compacted to at least
95% of the modified Proctor maximum
dry density. The total length of the GRS
foundation was about 459.3 feet (140 m),
and the replaced depth reached the gravel
stratum or bedrock with sound engineering
properties ranging from 9.8 to 16.4
feet (3 to 5 m).
2. GRS embankment
Figure 8 displays the schematic design
of the GRS embankment. The construction
was completed in three stages using
ACEGrid® GG150-I wrap-around facing
FIGURE 9 Construction of
the GRS embankment.
setback and an inclined ratio of 1:0.2
(vertical : horizontal). Each stage was
16.4 feet (5 m) high, and the width of
the step-back platform was 4.9 feet (1.5
m). The GRS embankment was built to
support highways, meaning the geogrid
configurations had to meet the highest
requirements for function and safety.
The geogrid was placed with a vertical
spacing of 0.9 feet (0.3 m) at the lowest
stage and 1.6 feet (0.5 m) for the other
two higher stages. The geogrids were
embedded at different lengths, with the
lower layer being 65.6 feet (20 m), the
middle layer being 61.7 feet (18.8 m),
and the upper layer being 55.8 feet (17 m)
as shown in Figure 9. Drainage boards,
geotextile filters, and porous gravels were
installed in each stage to intercept rainfall
infiltration or seepage effectively. In addition,
stacked soil-filled and hydro-seeded
sandbags (ACESandbag™ EC) were used
to protect the slope face and promote a
natural green aesthetic landscape.
The fill material was the excavated
materials from the nearby tunnel. It was
compacted to more than 95% of the modified
Proctor maximum dry density. In
addition, permeable material, 1.6 feet (0.5
m) thick, and high-density polyethylene
GeosyntheticsMagazine.com
19
Drainage boards,
geotextile filters,
and porous gravels
were installed
in each stage to
intercept rainfall
infiltration or
seepage effectively.
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