March/April 2022 - 79

weeks to complete. The TM 18/22
provided the depth reach and power
required to penetrate the soil profile.
Work was coordinated with the
contractor's construction sequence plan
and schedule, and proceeded around the
site to allow site/foundation work to
begin immediately following ground
improvement installation. During
construction, numerous obstructions
were encountered. Shallow obstructions
were easily excavated to allow pier
installation to proceed. Where deep
obstructions were encountered, the
Helical design team quickly redesigned
the ground improvement around the
obstruction, and additional elements
were installed (if needed) so production
could continue.
The final ground improvement
design included 1,200 ground improvement
elements, including about 640
GCCs and 560 RAPs . Whi l e in
production, Helical was able to install 25
to 70 elements per day. Production
varied based on material supply, site
access, element installation length,
tooling changeover/repair, weather, etc.
Conclusion
Urban projects are increasingly difficult
as available greenfield space near public
transportation in metropolitan areas
becomes harder to come by. Most sites
Geoconcrete column
installation
Alta XMBLY building completing construction
have been previously developed and, as
such, require engineers to not only
consider existing subsurface soils and
groundwater, but former developments
left behind. The Alta XMBLY site in
Somerville, Massachusetts, was no
exception. Located near Boston, the site
was previously filled land that had
many past industrial uses. The design
team conducted extensive subsurface
explorations that in part identified
urban fill overlying organics and a thick
marine clay layer. Based on site conditions,
the most economical approach to
support the new development that
included an 8-story building, and a grade
raise was to found the building on
shallow foundations following the
installation of deep ground improvement
(GCC) elements to limit long-term
settlements, and shallow rammed
aggregate piers to support the slab areas.
However, exploration revealed a
deep debris pocket from a former
development. Due to its depth, location
near the property line, a shallow
groundwater table, and environmental
concerns, the debris could not be removed
to allow for ground improvement.
The design and construction team
then developed a hybrid foundation
approach to provide the most costeffective
building approach by addressing
the debris-laden fill area separately
from the remainder. Ultimately, ductile
iron piles were installed with a sonic
predrill approach for cost-effectiveness
and efficient debris management. The
unique sonic technology enabled
penetration of steel and other debris,
while modular ductile iron piles could
be easily installed within the sonic drill
casing. When combined with the geoconcrete
column and rammed aggregate
pier ground improvement systems that
allowed conventional, shallow foundations
across the majority of the site, the
hybrid approach yielded a deflectioncompatible
foundation solution of
significant value to the owner.
Michael J. Weaver, P.E., is a senior associate and
director of field services for Haley & Aldrich in
Boston, Massachusetts. He has over 20 years of
experience in providing geotechnical and environmental
consulting services to public and private
clients and is responsible for the training and
development of the technicians and engineers
performing field work at Haley & Aldrich.
Michael Cronenberger, P.E., is the specialty
foundation division manager for Helical Drilling in
Braintree, Massachusetts, where he oversees the
piling, shoring and grouting projects for the company.
He has 6 years of geotechnical and structural
consulting experience and over 9 years of construction
project management and design experience.
Andrew Thompson, P.E., is a ground improvement
project manager for Helical Drilling in
Braintree, Massachusetts. He has over 17 years of
experience in geotechnical consulting and
design/build construction.
DEEP FOUNDATIONS * MAR/APR 2022 * 79

March/April 2022

Table of Contents for the Digital Edition of March/April 2022

TOC
March/April 2022 - Intro
March/April 2022 - 1
March/April 2022 - 2
March/April 2022 - TOC
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