DFI Magazine January/February 2020 - 80

The ambiguity in bog depth and
bedrock contact elevation, in combination
with adverse site conditions for large
excavations and pile driving equipment,
led to numerous foundation delays during
the early stages of the project. While
foundation retrofits were possible at some
of the problematic sites, several of the
installations required an alternate solution
that had not been previously contemplated. The project team began to explore
alternative options for these sites.

Alternative Considerations
The selected alternative(s) would need to
supplement grillage and driven pile
foundations in accommodating a wide
range of conditions, which included:
1. Cobbles and boulders within the
overburden material

Average alignment subsurface conditions

2. Variable depth to bedrock between
structures and within a structure's
footprint

Lattice structure with steel pile cap

3. Soft overburden overlying relatively
shallow hard bedrock
4. Soft surface conditions during periods
prior to freezing and during thawing
The foundations would also need to meet
the necessary capacity requirements.
Planned lattice structures for the project
would generate up to 472 kips (2,100 kN)
of uplift, 595 kips (2,650 kN) of
compression and 190 kips (850 kN) of
shear at each leg. Guyed structures would
generate up to 540 kips (2,400 kN) of
compression and 65 kips (292 kN) of shear
at the center pin. Uplift loads associated
with the lattice structures would require
significant pile embedment to develop
adequate foundation resistance.
Accessibility was not a driving factor
behind alternative foundation selection but
was certainly a consideration. Access roads
were constructed along the length of the
alignment, which came close to each
structure location but did not provide
direct access to each footing/foundation
site. In the winter months, the frozen
ground provided sufficient support for
most materials and equipment to traverse
this distance of approximately 50 to 100 ft
(15 to 30 m). In the summer months, with
boggy and wet conditions, matting was
required to bridge the gap.
80 * DEEP FOUNDATIONS * JAN/FEB 2020

Micropile Integration
Ultimately, it was determined that
micropiles, in combination with drilled
pipe piles and the existing grillage and
driven piles, would provide the optimal
solution. Micropiles can be readily adapted
onsite to accommodate a range of
conditions, which was crucial to the success
of this project. In addition, the equipment

and materials required for installation can
be relatively small and lightweight while
still achieving high capacities.
D e t a i l e d m i c ro p i l e f o u n d a t i o n
schedules were created for each site,
providing foundation capacities for a range
of expected conditions. Where subsurface
conditions required a combination of
foundation types, one-off and location-



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
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/march-april-2024
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/january-february-2024
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/november-december-2023
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/september-october-2023
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/july-august-2023
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/may-june-2023
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/Jan-feb-2021_nxtbook
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https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/march-april-2023
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/january-february-2023
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/november-december-2022
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/september-october-2022
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/july-august-2022
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/may-june-2022
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/march-april-2022
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/january-february-2022
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/november-december-2021
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/sept-oct-2021
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/july-aug-2021
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https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/november-december-2020
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/September-October-2020
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/may-june-2020
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/march-april-2020
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/january-february-2020
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/july-august-2020
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