DFI Magazine January/February 2020 - 82

intervals is recorded, and the total number
of blows required to drive the sampler from
6 to 18 in (15 to 45 cm) is referred to as the
SPT N-value. The N-value provides a
general indication of in-situ soil density
and consistency.
Specific construction challenges
included working in winter temperatures
close to -40°F (-40°C). To mitigate this, all
equipment included an on-board heating
system and insulation, a heated pressure
washer was used to clean the drill at the end
of each shift, all-thread bar and hardware
required heating to above 41°F (5°C) prior
to installation, and insulation blankets were
wrapped around grouted piles to protect the
fresh grout from freezing. When dust
control was not possible due to low
temperatures, the project team implemented a respirator fit test and management
program. To decrease safety concerns, crews
were equipped with climate-appropriate,
nonslip footwear and hand wear, and
encouraged to take regular breaks in warm
vehicles. In addition, lighting was installed
on all equipment to accommodate the short
daylight hours during winter months.
The relatively compact and lightweight
nature of micropile materials and
installation equipment was beneficial to
logistical concerns in all seasons. The
smaller items were sufficiently supported
on frozen ground in the winter and required
significantly less matting than other
foundation types in the wet/boggy spring
and summer conditions. Size was also a
factor when maintenance issues arose,
which were common given the climate.
Long, linear projects like this one mean that
foundation sites are often a significant
distance from staging yards and other
project amenities. The logistics of
transporting large pieces of equipment for
service and repairs can be much more
complicated than smaller pieces.

Testing and Quality Control
The foundation design team was supported
by field engineers and geologists who oversaw micropile installation and testing. One
micropile at each structure location was
proof tested to the specified design load.
Tension load testing was performed in accordance with ASTM D3689. Loads ranged
from 201 to 368 kips (965 to 1,635 kN) and
82 * DEEP FOUNDATIONS * JAN/FEB 2020

Erected lattice structure

the corresponding total displacements
ranged from 0.22 to 0.65 in (0.58 to 1.65
cm). The results from the proof tests
confirmed that the approaches taken to
mitigate subsurface challenges and related
design assumptions were successful.

Completion
On a project that was already facing
substantial weather and logistical
challenges, micropiles provided a key
component to ensuring successful
foundation construction. Their ability to
handle the unconfirmed and fluctuating
subsurface conditions was a major benefit to

both constructability and a schedule that
had seen delays. All foundations were
successfully installed, the prime contractor
met its substantial completion date, and the
Labrador-Island Transmission Link was
energized in 2018.
As power sources continue to be
developed in more remote areas, an
increasing number of transmission projects
are facing these logistical and engineering
challenges. Project conditions are restricting
equipment types and construction
methods, and foundations that were once
considered uncommon to the industry are
becoming more and more prevalent.

Steve Davidow, P.E., S.E., P.Eng, is senior vice president of engineering at Quanta Subsurface. He has more than
20 years of experience in the design of deep foundations, and currently serves as the DFI chair of the joint ADSCDFI Micropile Committee as well as co-chair of the DFI Electric Power Systems Foundations Committee.
Michael Davidson, P.E., is a seasoned project manager at Quanta Subsurface, overseeing major foundation
design-build programs. He has over 15 years of experience in drilling and heavy construction, and more than 5
years of concentrated experience in specialty deep foundation construction.



DFI Magazine January/February 2020

Table of Contents for the Digital Edition of DFI Magazine January/February 2020

Contents
DFI Magazine January/February 2020 - Intro
DFI Magazine January/February 2020 - Cover1
DFI Magazine January/February 2020 - Cover2
DFI Magazine January/February 2020 - Contents
DFI Magazine January/February 2020 - 4
DFI Magazine January/February 2020 - 5
DFI Magazine January/February 2020 - 6
DFI Magazine January/February 2020 - 7
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DFI Magazine January/February 2020 - Cover3
DFI Magazine January/February 2020 - Cover4
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