Geosynthetics June/July 2021 - 14

NPA geocell for a railway line repair in a permafrost region
This article discusses the design
This article discusses the
design and construction
methodology applied
using NPA geocell in fall
2018. Attempts made to
protect the permafrost
under the rail line have
also been explained.
Based on more than two
years of operation, this
article also recommends
a viable future of transportation
infrastructure
development method in
the permafrost region.
and construction methodology applied
using NPA geocell in fall 2018. The
findings are supported by design basis
and innovative construction practice,
photographs and construction reports.
Attempts made to protect the permafrost
under the rail line have also been
explained. Based on more than two years
of operation, this article also recommends
a viable future of transportation
infrastructure development method in
the permafrost region.
Geocells on
railway application
Pokharel (2010) and Han et al. (2010)
identified three key mechanisms of geocell
reinforcement as lateral and vertical
confinement, wider stress distribution,
and the beam or slab effect. The higher
stiffness of the geocell system reduces
the stress applied to the subgrade due
to the bending stiffness of the mattress
composite, similar to a slab (Pokharel
et al. 2011). On road pavement applications,
Norouzi et al. (2019) recommended
geocell reinforcement as the
reliable options under repeated loading
condition. Railway embankments also
undergo extensive cyclic loading and
must be able to withstand the applied
repeated load occurrences and, at the
same time, be economical and sustainable
in the long term. The need for a
more robust embankment structure
poses a huge challenge to the supply
of granular material that is of adequate
quality and is affordable (Pokharel et al.
2017). Where good-quality material is
not easily available, it requires a reliable
3D geosynthetic reinforcement. The ability
of geocells to use recycled, marginal
or poorly graded granular material helps
reduce the burden on the environment
and adds value to the design. In railway
applications for the reinforcement of
14
Geosynthetics | June July 2021
structural layers, geocells can be used
to reinforce the ballast or subballast to
improve the reinforced layer's modulus
and reduce the stress transferred to the
soft subgrades (Kief 2016). The NPA
geocells that were used in this project
enable the use of inferior-quality,
locally available granular material while
improving the modulus ratio over the
underlying surface by up to 7.6 times;
the higher strength and stiffness of the
geocell produces a higher improvement
factor (Pokharel 2010). This eliminates
the need for hauling high-quality granular
material and reduces associated CO2
emissions (Pokharel et al. 2016), making
NPA geocell an attractive option from a
sustainable-development perspective.
Leshchinsky and Ling (2013) reported
greatly reduced lateral spreading and
vertical deformations of the ballast when
reinforced with geocells. The benefit was
more pronounced when the railway substructure
overlies softer subgrades and
weaker ballast material was used. Palese
et al. (2017) conducted performance tests
on Amtrak's Northeast Corridor near
Havre de Grace, Md., in the U.S. with
NPA geocell reinforcement in the track
substructure. The material was selected
due to its strength and its creep resistance
properties for the Federal Railway
Administration (FRA) Class 7 track
that sees traffic from both high-speed
trains (125 mph [201 kph]) and regional
trains (110 mph [177 kph]). Palese et
al. (2017) reported significant reduction
in pressure at the ballast/subgrade
interface of 50% and a corresponding
reduction in the rate of degradation of
a factor of 6. Overall, the test based on
the pressure data from load cells placed
above the subbase directly beneath the
rails and track geometry data showed
significant benefits using NPA geocell
reinforcement above and beyond that
seen by more traditional rebuild and
drainage improvements.

Geosynthetics June/July 2021

Table of Contents for the Digital Edition of Geosynthetics June/July 2021

Geosynthetics June/July 2021 - Cover1
Geosynthetics June/July 2021 - Cover2
Geosynthetics June/July 2021 - 1
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