March/April 2021 - 79

CMC rigid inclusion installation for new 5-story structure

FEATURE

ARTICLE

Rigid Inclusions and Piles for Mixed-Use Redevelopment
 The project site encompasses an entire
city block in the heart of Pittsburgh's
historical Strip District, which was an
industrial site until approximately the
1950s, when it was converted to
warehouse space.
The plan for the site was to demolish
existing 2- and 5-story buildings,
leaving only the 4-story building
standing. The façade of this adjacent
4-story building (back left of photo)
remained, with the interior becoming
new retail and office space. Two new
stairwells and elevators shafts were
added within the existing 4-story
structure to service the new office
spaces. A new 5-story structure on the
southwest portion of the site would
consist of ground-level retail space with
a 4-story parking garage. The soils had a
compressible nature at the site, so
Menard recommended ground

AUTHORS

improvement using controlled modulus
column (CMC) rigid inclusions to
support the 5 stories. Due to the low
overhead conditions within the existing
4-story structure, Menard recommended
Magnum design the helical piles to support the new stairwells, elevator shafts
and below-grade ramp into the garage.

Boring Coverage
Performing soil borings on site was a
challenge because of existing structures. During the bid phase, borings
located approximately 600 ft (182.8 m)
away at an adjacent site were used to
approximate soil properties (see later
boring map). During final design, a
geotechnical investigation was performed, but was limited to the parking
lot area, as the 2- and 5-story buildings
had yet to be demolished. The closer
borings were used to refine the ground

improvement design; however, the
majority of the site still did not have
boring coverage.

Site Conditions
Due to the location in a historic
industrial area near the Allegheny River,
site conditions vary greatly within just a
few feet. Generally, the soils consist of
medium-dense to very dense fill from
existing grade, at an elevation of 729 ft to
718 ft (222 m to 219 m), underlain by
medium-stiff clay to an elevation of
704 ft (215 m), followed by a mediumdense to dense sand and gravel bearing
layer. Groundwater was present at an
elevation of 716 ft (218 m). The entire
Strip District previously occurred at a
lower elevation. After a historical
flooding event, though, the entire Strip
District became filled with rubble and
other material, often including building

Nina F. Carney, P.E., Menard Group USA; Melinda J. Hummel, P.E., Magnum Geo-Solutions; and Nathaniel Witter, P.E.,
Nicholson Construction Company
DEEP FOUNDATIONS * MAR/APR 2021 * 79



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