Geosynthetics October/November 2022 - 17

review of thousands of daily wick drains
installations and identification of installation
issues significantly more efficient
than traditional manual methods. An
automated system has proven to be an
important addition for a large wick drain
installation project.
Instrumentation requirements
As noted in Part 1 of the article, vibrating
wire piezometers (VWPs), settlement
plates (SPs) and slope inclinometers
(Sis) were installed to monitor the
performance of the stockpile. VWPs
were installed at the critical locations to
measure the dissipation of excess pore
water pressure following loading. An
important part of the VWP installation
was that at each location, paired VWPs
were installed close to each other but
separated by a minimum two rows of
wick drains. The rationale behind this is
that if one or more wick drains adjacent
to a VWP clogs, that VWP may indicate
a slow dissipation of excess pore water
pressure that may not be representative
of the unclogged wick drains in the larger
area. Such a condition could result in
unjustified warnings and concerns on
the performance of the wick drains. The
installation of additional adjacent VWPs
helps in identifying the source of a possible
problem where elevated pore water
pressure is observed. Potential causes
of elevated pore water pressures could
include clogging of the wick drains adjacent
to the VWPs or too rapid a rate of
stockpile raise.
SPs measure the consolidation settlement
of the clay. This provides an independent
method to confirm the excess
pore water pressure dissipation measured
in the VWPs and associated clay foundation
strength gain.
SIs were installed at the critical locations
to measure lateral ground movement
and to identify the development of a shear
layer within the foundation clay.
345.0
350.0
355.0
360.0
365.0
370.0
Fill Above Tip
OGE
62885 Piezo Elev
62885 Tip Elevation
62331 Piezo Elev
62331 Tip Elevation
Rain (mm)
340.0
Jun-2020
Aug-2020
Sep-2020
Nov-2020
Date
FIGURE 4 Stockpile VWP results
Figure 4 shows the dissipation of
excess pore water pressure following the
fill placement at two VWP locations over a
relatively short period. As shown, the wick
drains are functioning well as expected
and satisfy the design requirements.
Conclusions
This article provides details on the construction
of a very large wick drain project
carried out in North America.
Part 2 of this paper discusses unique
features of the project, which include
considerations regarding the surface
grading of the drainage blanket to provide
a suitable working platform for wick
drain rigs, wick drain materials and high
confining ground pressure that the wick
drains will experience, the effect of a
dense layer, wick drain mandrel bending,
cold weather considerations, automation
of the wick drains installation data and
data processing, and instrumentation
requirements. Appropriate attention to
the construction considerations provided
in this article was developed throughout
the project by the owner, contractor and
designer, which resulted in the overall
success of the project. G
Jan-2021
Feb-2021
Apr-2021
0.0
5.0
10.0
15.0
20.0
25.0
30.0
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17
Elevation (m)
Precipitation (mm)
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Geosynthetics October/November 2022

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