Geosynthetics June/July 2021 - 18

NPA geocell for a railway line repair in a permafrost region
Type D geocell, and layers below were
reinforced with Type C geocell. Both
NPA geocells were perforated, 6-inches
(150-mm) high and had 13 inches (330
mm) between seams. The properties of
the geocells used are given in Table 1.
The nonwoven geotextiles had a grab
As the access was limited,
the work needed to be
completed with a limited
amount of construction
equipment-whatever
could be transported
to the site by available
means. Even the daily
commute for the construction
crew from the
nearest camp in Gillam
on road-rail vehicle was
six hours round-trip.
tensile strength of 205 pounds-force
(911 N) and 299 pounds-force (1,330 N)
with 50% elongation on grab. The woven
geotextile had a grab tensile strength of
200 pounds-force (890 N). Nonwoven
geotextiles were used on top of subgrade.
Construction methods
Photographs and videos of the damaged
area were made available but not the survey
of other engineering data available
for the design. An aerial survey was conducted
to assess the extent of the damage
and required repair work at the washout
locations to resume rail traffic. It was
assessed that the project would be a linear
construction, and access to the next location
would be available only after completing
work at the preceding location.
The designers reached the first damaged
site by rail and walked to the next locations
to access the damage and check the
suitability of the design and construction
methods. As the access was limited,
Properties
Material
Wide-width strength at yield
Cell height of geocell
Distance between weld seams
Coefficient of soil-cell friction efficiency
Coefficient of thermal expansion
Brittle temperature
Long-term plastic deformation at 65°C (load 6.6 kN/m)
Dynamic (elastic stiffness) modulus at 30°C
TABLE 1 Properties of NPA geocell used in the design
18
Geosynthetics | June July 2021
Type C geocell
Polymeric nano composite alloy
19 kN/m
150 mm
330 mm
0.95
<135 ppm/°C
<-70°C
3.00%
>775 MPa
22 kN/m
150 mm
330 mm
0.95
<135 ppm/°C
<-70°C
3.00%
>800 MPa
the work needed to be completed with a
limited amount of construction equipment-whatever
could be transported to
the site by available means. Even the daily
commute for the construction crew from
the nearest camp in Gillam on road-rail
vehicle was six hours round-trip.
There was limited space to work in the
repair locations, as the construction team
was told to work within the railway rightof-way.
Transporting heavy equipment
that could be accommodated within the
width of the railway line was out of the
question. The construction team followed
the geosynthetic installation procedures
per the manufacturer's installation guide,
and experience-based compaction methodology
was applied for compacting the
granular fill at the subballast and layers
below. The lower layer of the granular fill
was compacted to the possible extent to
protect the permafrost layer. As there was
no facility to do compaction testing, ruts
developed by the 4-ton (3.6-tonne) compactor
were used as an indicator of the
required degree of compaction. A maximum
rut of 0.5 inch (12.5 mm) under the
roller wheel was considered as equivalent
to 95% compaction for upper layers.
Twelve passes of the compactor were
made to meet the minimum compaction
criteria at each location. Figures 4-8
Type D Geocell

Geosynthetics June/July 2021

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Geosynthetics June/July 2021 - 1
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