Geosynthetics June/July 2022 - 26

Improving railway drainage with multi-linear geocomposites
Response time Draintube vs Granular layer
30'
25'
20'
15'
10'
5'
0'
-
5
10
15
20
Slope (%)
FIGURE 9 Drainage response time
DRAINTUBE versus granular layer
PROJECT HIGHLIGHTS
DRAINAGE IMPROVEMENT
UNDER TRACKS
OWNER
Canadian National Railway Co.
LOCATION
Quebec, Canada
GENERAL CONTRACTOR
KPH Inc.
ENGINEERS
Journeaux Assoc.
GEOSYNTHETIC PRODUCT
DRAINTUBE 500P TF4 D25
GEOSYNTHETIC MANUFACTURER
AFITEX-Texel Geosynthetics Inc.
26
Geosynthetics | June July 2022
Case study: Drainage
improvement under tracks
Within the scope of work for some track
reconfigurations, engineers must design
alternative drainage systems because of
the limited space available in certain track
corridors. A multi-linear drainage geocomposite
with mini-pipes can be used
to efficiently evacuate the water below the
tracks. The mini-pipes carry water flow to
a ballast drain or an open ditch.
In 2016 a Canadian National Railway
Co. project in Quebec required two tracks
to be drained into either an open ditch or
a ballast drain installed 3 feet (1 m) below
track level. Without a proper system,
potential drainage problems and a shortened
life for the ballast would occur. The
geocomposite with mini-pipes was placed
directly under the ballast (Figure 9). The
mini-pipes in the product had a diameter
of 0.8 inch (20 mm) and a spacing of 10
inches (254 mm) center-to-center.
Construction crews unrolled the
multi-linear drainage geocomposite perpendicular
to the tracks directly on the
MG-56 subgrade soil. Afterward, they
25
installed the ballast in two layers of 5.9
inches (150 mm) each.
Engineers designed the multi-linear
Granular layer,
20 in. thick
Draintube
drainage geocomposite to evacuate rainfall
of 26 inches per day (661 mm/day)
with the mini-pipes remaining unsaturated
(Ruel et al. 2018). The 100 years
return period rainfall in Quebec is 6.1
inches per day (156 mm/day). Assuming
only the geocomposite drains all rainfall,
its drainage capacity is more than four
times greater than required, considering
the long-term hydraulic behavior of the
geocomposite under the critical conditions
of the application.
From Del Greco et al. (2012), using
30
35
an 8.2 foot (2.5 m) long and 6.6 foot (2
m) wide inclinable open box with rainfall
simulator on top, it was shown that
a multi-linear drainage geocomposite
enables rainfall to evacuate faster than
a granular drainage layer. This is due to
the directional aspect of the product. The
water is drained into the mini-pipes even
in situations where the slope is zero.
That behavior is significant for low
slopes when the rainfall water must be
evacuated rapidly before building up
into the overlying layer or infiltrating
into the subgrade.
Conclusion
DRAINTUBE multi-linear drainage geocomposites
with mini-pipes have been
used successfully on many earthworks
projects, including railway construction
projects. Depending on the project and the
design considerations, the geocomposite
is used either for embankment and subsurface
drainage on cut slopes as a replacement
for granular layers or for drainage
improvement under railway tracks.
References
ASTM D2412. (2021). Standard Test Method for
Determination of External Loading Characteristics of
Plastic Pipe by Parallel-Plate Loading. American Society
for Testing and Materials, West Conshohocken, Pa.
First liter drainage (min)
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