July/August 2023 - 98

2114/2116 14th St. NW
Standing 34 ft (10 m) in height, this twostory
brick building required the
preservation of all exterior brick walls,
the second-floor concrete slabs and
concrete columns.
The scope of work consisted of
underpinning the existing brick facade
at the east and the exterior west wall to
provide vertical support as well as to
provide temporary support for the
excavation (for lateral soil retention).
The existing brick building required
shoring to allow for the demolition of
the foundation, the slab on grade and
concrete roof while enabling the
construction of the new structure.
Challenges: The vertical concentrated
loads were too high for a fullbearing
shoring and underpinning
system given the soft and wet grounds
at subgrade elevation. Therefore, the
shoring and underpinning systems
needed to incorporate deep foundations
(micropiles).
More than half of the total number
of micropiles needed (60 in total) were
to be installed from within the existing
building. The second-floor slab (to
remain), and the 4.5 ft (1.3 m) deep concrete
beams supporting this slab, created
considerable headroom limitations.
There was a substantial amount of
existing and proposed columns at the
north and south walls that made the
needle shoring of these existing walls
and columns complex and meticulous.
Contaminated soils were encountered
during the excavation
process, which could have substantially
impacted the schedule if
careful and considerate coordination
had not occurred.
Solutions: The underpinning
system provided was designed to resist
the vertical loads by using resistance
forces from a combination of the piers'
allowable bearing capacity and the
geotechnical capacity of the micropiles.
The idea behind this combined system
was to use the micropiles to limit the
vertical loads transferred into the
concrete piers, thus reducing the
bearing pressure under the piers to
acceptable levels.
Micropiles - The micropiles were
pressure-injected grouted elements
7 in (180 mm) in diameter, made of grade
80 steel casing reinforced with 52/26
Titan IBO bars. The maximum load acting
on the micropiles was 90 kip (400 kN).
98 * DEEP FOUNDATIONS * JULY/AUG 2023
2114/2116 14th St. NW

July/August 2023

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

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July/August 2023 - Intro
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