March/April 2022 - 77

months prior to installation of ground
improvement elements.
The ground improvement approach
was suitable for all areas of the site
except in the southwest corner, where
up to 19 ft (5.8 m) of debris was
encountered. Given the proximity of the
area to the property line, the shallow
groundwater table and environmental
concerns related to excavation of the
s o i l a n d ma n a g eme n t o f t h e
groundwater, the debris could not be
removed prior to GCC installation.
Since the presence of the debris would
not allow for the advancement of the
GCC elements, an initial solution
involved micropiles advanced through
the debris, clay and glacial till to
transfer the building loads into
competent rock. The project team
recognized that a micropile solution
had its drawbacks. That is, it would
solve the constructability issues but
result in a slow, expensive foundation
installation.
Working closely with the project
team, engineers with geotechnical
subcontractor Helical Drilling considered
solutions to advance a hole
through the debris that would then
allow for a driven pile system. With
successful use of sonic drilling on other
projects, Helical solicited the expertise
from Eijkelkamp North America and
their sonic drilling technology to
provide a solution that would enable
debris penetration. The low amplitude,
high frequency operation of the sonic
drilling action allows its tooling to be
advanced through reinforced concrete
and even solid steel, which comprised
many of the obstructions (see the
July/Aug 2020 Deep Foundations cover
story for more about sonic drilling). It
was determined that a Mito 60 sonic rig
would provide the necessary features
by drilling 12.75 in (0.32 m) diameter
holes through the debris.
Although a technique had been
identified to advance through the
debris and provide a cased hole, a
suitable deep foundation system was
needed that could efficiently work with
sonic drilling to limit the installation
duration and foundation costs. With
limitations set on the hole diameter
that would penetrate obstructions
while still providing a cased hole, use of
GCCs was not practical. It was also
determined that the installation
schedule would be controlled by the
duration of the sonic drilling. Further,
pile installation needed to proceed
immediately so that the tooling could
be removed and used on the next hole to
limit the predrilling cost. After studying
several options, both traditional drilled
micropiles and ductile iron piles (DIPs)
were considered viable.
Cost estimates were performed for
both systems. Engineers at Helical
quickly realized that a small diameter,
modular DIP solution would be more
economical than micropiles. The DIP
approach would limit the predrill hole
size and extend through the fill, organics
and marine soils to terminate in dense
glacial till or rock. Haley & Aldrich's
experience with this technique on other
local projects provided the project team
confidence the DIP system would
perform well at the site.
Ductile Iron Pile Use
After concluding that ductile iron piles
provided economic and schedule
advantages, a full-scale preproduction
load test was initiated to confirm design
capacities. A pile section and capacity
optimized for the building loads in this
area was selected that would minimize
the number of predrilled holes and
provide settlement compatibility for the
nearby GCC-supported foundations.
A Series 170/9.0 pile size with a
Site plan with boring locations, areas of debris fill
170 mm (6.7 in) diameter and 9 mm
(0.35 in) wall thickness was selected to
support a compression design load of 85
tons (756 kN). A test pile location was
selected just outside of the buried debris
area and near the location of a deep
boring advanced to bedrock. The
sacrificial ductile iron pile was driven
with a Tramac V1800 percussion
hammer and advanced to rock at a depth
of 78 ft (23.8 m), where a termination
criterion of 1 in (25 mm) or less in 50
seconds of driving was established. The
test pile was instrumented with three
sister bar strain gauges. Following the
standard axial compression load test
requirements of the Massachusetts
State Building Code, loads were
increased in 25% increments to a
maximum load of 200% of design.
DEEP FOUNDATIONS * MAR/APR 2022 * 77
March/April 2022

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