July/August 2023 - 99

Micropiles were designed to obtain
their geotechnical capacity in the
denser terrace formation layer, which
consisted of poorly graded gravel and
poorly graded sand. The lengths of the
micropiles installed, for the underpinning
and shoring, were between
40-45 ft (12-13 m).
The initially calculated micropile
capacity was confirmed via a load test
program performed on a sacrificial
micropile that was loaded to 1.5 times
the maximum design load. Test piles
were installed from existing grades
using the same method as a production
pile. However, the bars were covered
with PVC pipes above the proposed
subgrade elevation to intentionally
break the bond that could develop above
this elevation, yielding results that were
representative of the production piles.
Underpinning System - The underpinning
system provided for the east
and west walls consisted of alternating
unreinforced concrete piers, with reinforced
concrete lintels and lagging in
between, bearing on two micropiles each.
The unreinforced concrete piers
were 4 ft (1.2 m) long by 2.5 ft (0.7 m)
wide by 13 ft (4 m) deep. Piers were
internally braced with inclined rakers
at each pier, bearing on concrete heel
blocks.
Shoring System - The shoring was
designed to provide lateral and vertical
support to the structural components of
the existing two-story building that
were to remain and was coordinated
with the proposed building to avoid
conflicts.
The system consisted mainly of two
sets of runner beams, spanning the
east-west direction and bearing on
micropiles. Sitting on top of the runner
beams were a total of 52 needle beams
approximately 10 ft (3 m) in length,
spaced at no more than 5 ft (1.5 m) on
center. Then, a combination of lateral
braces and vertical steel posts were
used to transfer the lateral and vertical
loads into the micropiles; essentially
DEEP FOUNDATIONS * JULY/AUG 2023 * 99
unloading the columns to allow for the
detachment and demolition of their
respective footings. The shoring held
the existing building 17 ft (5.1 m) in the
air allowing for the new below grade
structure to be constructed.
2124 14th St. NW
Initially, the scope of work included
shoring the existing brick building so all
the exterior walls remained, allowing
for the demolition of the foundation,
slabs and concrete roof. The exterior
2124 14th St. NW
brick walls were to be shored using a
steel frame composed of runner and
needle beams bearing on steel posts,
similar to the one provided at building
2114/2116. However, as part ial
demolition started to take place, and the
structural " skeleton " of the building
was exposed, it was determined that the
existing conditions of the brick walls
were too deteriorated to be salvaged.
Only the front facade of the building
(which had significant historical value)
was able to be preserved.

July/August 2023

Table of Contents for the Digital Edition of July/August 2023

TOC
July/August 2023 - Intro
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July/August 2023 - 2
July/August 2023 - TOC
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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
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/july-august-2021
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/march-april-2021
https://www.nxtbook.com/dfi/DEEP-FOUNDATIONS/january-february-2021
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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