Geosynthetics June/July 2020 - 22

High-strength geocell and geogrid hybrid reinforcement

conventional design, highlighting the
challenges faced during the construction
and the performance of the structure.

Geosynthetic reinforcement
for load support

This article discusses
hybrid geosynthetics
reinforcement design
to support a heavyloaded gravel pad
for the compressor
station and compares it
with the conventional
design, highlighting
the challenges faced
during the construction
and the performance
of the structure.

22

Planar geosynthetics have been used as
soil reinforcement for many years; threedimensional geocells are comparatively
new. Geocell reinforcement usually utilizes geotextile for separation. Geogrid
improves the stiffness of the reinforced
soil by interlocking, lateral restraint and
tension membrane; it reduces the applied
stress on the soft soil and increases the
bearing capacity while decreasing settlement (Qian et al. 2013). The performance
of geogrid depends on aperture size and
shape, material stiffness at junctions,
and shape and stiffness of ribs (Giroud
and Han 2016). Ever since the U.S.
Army Corps of Engineers used geocell
for reinforcing beach sand in the 1970s
(Webster 1979), numerous research programs, experiments and monitored applications have been carried out to further
understand the geocell-reinforcement
mechanisms (Han et al. 2013). Vertical
and lateral confinement, wider stress distribution and beam/slab effect are identified as the main reinforcement mechanism
of geocell. Higher tensile stiffness, strength
and creep resistance of geocell material
provide the reinforced base with improved
bearing capacity, higher modulus and
extended design life (Pokharel et al. 2010,
Thakur et al. 2013 and Kief et al. 2015).
High-strength NPA geocell reinforcement
also improves the creep resistance of the
reinforced structure, which is a very
important factor in the repetitive loading
conditions, as it significantly reduces the
initial deformation and rate of creep of the
reinforced material (Thakur et al. 2013).
A design method using NPA geocell reinforcement for unpaved roads
was developed by modifying the Giroud

and Han (2004) method for planar
reinforcement for rut criteria (Pokharel
2010). This method has already been
employed to design unpaved roads in
various projects and has been verified by
Pokharel et al. (2015). Design using NPA
geocells has been successfully employed
in paved and unpaved roads and other
geocell-reinforced, load-bearing earthen
structures (Pokharel et al. 2013, 2015 and
2017, and Norouzi et al. 2017).
The authors have encountered several cases where a hybrid design with
geogrid and geocells make the project
structurally sound and economically feasible. Sitharam and Hegde (2013) recommended a high-strength geocell and
geogrid hybrid design as an alternative
to ground improvement in soft soil that
could improve the bearing capacity of
the foundation by four to five times. Kief
(2015) reported reduction in maintenance
cycles and cost, showing the efficacy of
the hybrid geosynthetic solution by use of
biaxial geogrid and NPA geocells.

The project and hybrid design
The compressor station had two pads
adjacent to each other. Pad A was constructed earlier in the summer and the
pad under consideration is Pad B. Pad A
had faced several challenges due to soft
soil at the surface. The construction of
Pad B was planned for summer of 2016
but was delayed as the existing soil on-site
was found to be of very poor strength.
There were uneven and differential settlements under previously placed wooden
mats and the existing silty clay soil was
not suitable to support the expected loads.
After removal of the mats, the equipment
and trucks were stuck on the clay surface;
the depressions right under the truck tires
were as deep as 35.4 inches (900 mm).
To avoid the difficulties faced earlier, the
owner decided to look for an alternative
solution for Pad B.

Geosynthetics | June July 2020

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Geosynthetics June/July 2020

Table of Contents for the Digital Edition of Geosynthetics June/July 2020

Geosynthetics June/July 2020 - Cover1
Geosynthetics June/July 2020 - Cover2
Geosynthetics June/July 2020 - 1
Geosynthetics June/July 2020 - 2
Geosynthetics June/July 2020 - 3
Geosynthetics June/July 2020 - 4
Geosynthetics June/July 2020 - 5
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