March/April 2021 - 82

Care had to be taken when cobbles
and obstructions were encountered so
that the drill casing did not kick out of
alignment, which would have caused
pile location tolerance issues. The
down-hole hammer had no trouble
getting past these obstructions,
however.

Micropile Load Test

A skid steer with torque motor to install helical shaft

competent rock. The piles ended up
being drilled 65 ft (19.8 m) from the
ground surface.
The tight working space was the
biggest challenge, and required temporary modifications to the drill mast
during mobilization. At the time of
micropile installation, the flooring
above the stairway was cut out, which
significantly helped with setting up the
drill rig at the pile locations. The drill rig
used had to be in the excavation to drill
the piles, and the small area where the
concrete slab was cut out made
maneuvering the drill tedious.
CMC installation near 4-story building façade

One maintained compression test was
completed. It was a challenge to get the
reaction piles and test pile aligned to
have the correct spacing, while
avoiding the production locations, and
allowing a large enough area to support
each end of the test beam. The final
setup required approval to have the
reaction and test pile spacing reduced
to 6 ft (1.8 m). The ends of the beam then
sat on the concrete slab on each end.
The reaction anchors were prestressed
so that the beam would not lift off the
supported ends when the test was
performed. The test was very
successful and had less than 0.25 in
(0.64 cm) of total deflection at the 200%
test load (80-kip [356kN]); the net
settlement was 0.03 in (0.08 cm).

Conclusion
Menard worked closely with the
general contractor and structural
engineer to successfully execute the
ground improvement design and build
the 5-story garage.
Menard, together with Magnum
Piering (affiliated with Magnum GeoSolutions), designed a helical pile
system to support the 4-story stairwells, elevators and garage ramp. The
subgrade was unexpected and had
cobbles in some areas, and a weaker
bearing stratum in others. The team
quickly worked with the owners and
determined the additional helical piles
needed to meet the deflection criteria.
Areas that were not penetrable with
helical piles were switched to micropiles that were designed by Nicholson.

82 * DEEP FOUNDATIONS * MAR/APR 2021

Approximately 62 helical piles were
installed within stairwell A, the two
central elevator shaft locations and the
interior garage ramp, and 20 micropiles
were installed in stairwell D.
The teamwork of the three companies and the owners led to costeffective solutions to complete the
project in a safe and timely manner.

Micropile installation within 4-story building

Nina Carney, P.E., is a senior design engineer for
Menard Group USA with over 10 years of
experience. Carney specializes in the design of
various ground improvement techniques and
provides construction support to aid in the safe
execution of projects with the highest degree of
quality.
Melinda Hummel, P.E., is the engineering
manager for Magnum Geo-Solutions, the
engineering support company for Magnum
Piering. Hummel has over 7 years of experience in
the design of deep foundation solutions and has
written several technical papers and presentations for conferences.
Nathaniel Witter, P.E., is a project manager for
Nicholson with over 6 years of experience in
geotechnical construction including techniques
such as high-capacity post-tensioned anchors,
micropiles, CFA piles, compaction grouting, rock
grouting, and design and construction of various
support-of-excavation methods.

March/April 2021

Table of Contents for the Digital Edition of March/April 2021