Geosynthetics August/September 2022 - 24

Construction considerations for wick drain ground improvements
VWPs and inclinometers were installed
in boreholes and grouted in place
using a Portland cement-water-bentonite
grout backfill selected to be appropriate
for the surrounding soil stiffness.
Inclinometers were anchored a minimum
of 10 feet (3 m) into bedrock to
provide a stable anchor point.
The VWPs were installed to measure
Laboratory testing
was carried out
on representative
samples of
geosynthetic and
drainage blanket
materials used
for construction.
the pore water pressure dissipation following
the loading of the stockpile and
to monitor the performance of the wick
drains. Settlement plates were installed to
measure the foundation settlement during
and following the construction of the
waste stockpile. Slope inclinometers were
installed to monitor the foundation clay
deformation and the stability of the stockpile.
Monitoring threshold levels and the
appropriate responses were provided.
VWPs were installed at several depths
at locations centered between the adjacent
wick drains. The VWP cables were
mainly placed in trenches within the top
of the clay foundation or within the drainage
blanket and brought to the toe of the
stockpile, where they were connected to
data loggers. The VWP cables were snaked
along the base of the trench allowing for
ground settlement that is expected to
occur during stockpiling. Inclinometers
were installed close to the stockpile toe
and incorporated telescoping sections to
accommodate anticipated settlements.
Construction quality control
and quality assurance
Construction monitoring consisted of
construction quality control (CQC) and
construction quality assurance (CQA)
programs. CQC refers to measures implemented
by the contractors to verify that
materials used in construction and their
workmanship meet the project requirements.
CQA refers to measures implemented
by owner or owner's representative
to ensure the contractor's conformity to
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Geosynthetics | August September 2022
the CQA plan, the construction drawings,
the technical specifications and any field
changes implemented during construction.
CQA includes reviewing the CQC
plan, monitoring construction activities,
verifying the suitability of construction
material properties both visually and
through laboratory testing, documenting
on-site and off-site testing procedures and
results, and ensuring quality workmanship.
Earthworks visual inspections were
routinely performed to verify compliance
with the construction drawings, the technical
specifications and design changes
implemented in the field. Earthworks
inspections focused on confirming the
use of suitable equipment, materials, lift
thickness, compaction effort, and geosynthetic
material coverage, overlap and
quality. Additionally, inspections of the
stripped subgrade, the prepared subgrade
and the completed drainage blanket surfaces
were carried out. Laboratory testing
was carried out on representative samples
of geosynthetic and drainage blanket
materials used for construction.
CQC data were provided by the wick
drain contractor through rig-mounted
data acquisition systems. The data systems
recorded information on the rig
ID, wick ID, installation location, depth,
inclination, heading, penetration rate
with depth and crowd force with depth.
Wick drain installation data were
reviewed as a CQA measure to confirm
that wick drain installation was consistent
with the intent of the construction drawings
and technical specifications requirements
and changes implemented in the field,
as required and appropriate. The review
included verifying the 7-feet (2-m) wick
spacing, refusal depth, missing installations,
wick drain inclination and crowd force
data. Data were analyzed using CAD Civil
3D software. CQA visual inspections of
the wick drain installation was performed
daily to confirm the use of suitable wick
drain material, wick drain rig inclination
Geosynthetics August/September 2022

Table of Contents for the Digital Edition of Geosynthetics August/September 2022
