Geosynthetics October/November 2022 - 14

Construction considerations for wick drain ground improvements-Part 2
0.8%
essential condition for the performance
of the wick drains.
Practically, parallel installation of
0.5%
1.0%
1.1%
1.0%
1.1%
0.5%
0.5%
1.0%
0.5%
0.1%
wick drains can be achieved either by
installing all wicks vertically or by installing
them at a uniform inclination along
a rig heading that is parallel to the dip on
the plane of the drainage blanket.
If the second option is selected, the
0.5%
0.3%
0.3%
0.3%
0.3%
FIGURE 2 A typical wick drains
installation orientation plan
to be installed along consistent parallel
vectors. To facilitate parallel installation
of wick drains, the drainage blanket
surface must be uniformly graded with
minimal concave or convex features.
Where the drainage blanket surface has
concave changes in grade, wick drains
would diverge at depth beyond the 7-foot
(2-m) design spacing. The resulting
increased wick drain spacing at depth
would result in dissipation times that
are greater than those used in the design.
This could result in a significant decrease
in the allowable rate of stockpile raising,
which cannot be accommodated by the
mining plan.
While tip divergence could be corrected
by carefully plumbing the rig and
the mast at each wick drain location, such
plumbing is tedious and would considerably
reduce the productivity of the installation
rigs. As a result, providing simple
planar drainage blanket areas to facilitate
parallel wick drain installations is an
14
Geosynthetics | October November 2022
wick drain installation will be installed at
a constant inclination from vertical and
azimuth (i.e., an installation vector) perpendicular
to the mean drainage blanket
surface. This installation vector will need
to be consistently maintained within predefined,
uniformly graded areas, across
time and differing installation rigs. It
would still be necessary to check and set
the installation vector of the mandrel for
each wick drain installation and to provide
construction quality control (CQC)
verification of the installation details. For
this project, this method was anticipated
to be more challenging than simple vertical
installation of the wick drains.
The drainage blanket grading surfaces
were designed based on the wick drain
installation rigs' mast adjustment range
of approximately +/- 6°, so that the wick
drains could all be installed vertically.
As the mast of the wick drain installation
rig can only be adjusted in the fore
and aft direction (i.e., parallel to the rig
tracks), it was necessary for the rigs to
move back and forth along a constant
installation direction, parallel with the
dip direction on each planar section of
the surface grade.
Due to the large size of the wick drain
installation area, it was not possible to
provide a single uniformly sloped surface
for the entire wick drain area. To reduce
cut and fill regrading costs, the wick
drain area was divided into a number of
planar segments with differing surface
slope grades and directions. A wick drain
installation rig heading direction was
specified for each segment parallel to dip
2.5%
4.4%
4.2%
4.2%
4.2%
2.5%
4.1%
2.1%
4.1%
2.1%
3.7%
2.1%
4.1%
3.7%
3.7%
3.7%
Geosynthetics October/November 2022

Table of Contents for the Digital Edition of Geosynthetics October/November 2022
