May/June 2021 - 19

measurements to force and velocity time histories during
application of the loads. A load cell was also used to record
the impact forces of the applied test loads. The total ram
weight was approximately 33 kips (147 kN), with drop
heights ranging from 6 to 18 in (15 to 46 cm). This data was
used to measure driving stresses, evaluate pile structural
integrity and estimate approximate pile length and ultimate
axial compression capacities.
Case pile analyses program (CAPWAP) analyses were also
performed; this allowed computing of soil resistance forces
and approximate distribution along the pile embedment
based on the force and velocity data recorded during dynamic
testing. The CAPWAP analyses indicated that the piles
derived their total capacity through a combination of shaft
skin friction and end bearing, with approximately 50% to 75%
of the total capacity in end bearing.
For the Phase 1 testing, the measured ultimate geotechnical
axial capacities of the piles, based on statnamic tests,
were 477 kips and 524 kips (2,122 kN and 2,331 kN), or
allowable axial capacities of 239 kips and 262 kips (1,063 kN
and 1,165 kN), respectively. Based on the dynamic testing, the
piles' axial capacities were 890 kips and 995 kips (3,959 kN
and 4,426 kN), or allowable axial capacities of 356 kips and
398 kips (1,584 kN and 1,770 kN), respectively. For the Phase 2
testing, the ultimate geotechnical axial capacities of the piles
tested were 603 kips and 601 kips (2,682 kN and 2,673 kN), or
allowable axial capacities of 302 kips and 300 kips (1,343 kN
The observed pile set (pile head deflection per blow) from
all testing ranged from about 0.02 to 0.30 in (0.5 to 7.6 mm),
depending on the applied load during testing. The PDA and
CAPWAP estimates of total capacity should be considered
lower bounds, and the full soil and weathered rock resistance
may not have been fully mobilized, especially at the pile tip.
The relatively low pile deflections (set) further suggest that
the piles are embedded in the weathered bedrock strata. The
piles would likely have a higher capacity if a higher load cycle
or stroke height was applied. However, higher test loads could
have resulted in structural damage to the piles and were
deemed unnecessary considering the low structural capacity
of the pile repair.
Conclusion
The design team collaboration resulted in a successful, costefficient
pile load testing program for the existing pier piles.
The results demonstrated that the piles were installed to
capacities well in excess of the back-calculated numbers for
the previous manufacturing facility. Based on the pile set
between 0.1 and 0.3 in (2.5 and 7.6 mm), it is anticipated that
the piles could achieve additional capacity past the
maximum structural design loads.
The higher capacities determined during the pile load
testing program permitted the structural engineer and
developer to achieve the maximum number of floors for the
structures during final design of proposed buildings on the
pier. These additional units will assist in fulfilling the 2014
Boston plan to develop 53,000 new units of housing there by
2030 to manage a projected population increase of 20%. The
pile capacities also increased the return on investment for the
developer and owner. Ultimately, this project will provide
public access to Pier One so local residents and visitors are able
to take in the views of Boston Harbor and the skyline from the
pier and to further benefit from the waterfront's revitalization.
Example statnamic load test results
and 1,334 kN), respectively, based on statnamic testing; they
ranged from 670 kips to 940 kips (2,980 kN and 4,181 kN),
or allowable axial capacities of from 268 kips to 376 kips
(1,192 kN to 1,673 kN), respectively, based on dynamic testing.
The combination of statnamic and dynamic pile load
testing provided consistent results, showing the pile
capacities averaged over 300 kips (1,334 kN), which directly
related to the maximum allowable capacity of the pile repair.
John P. Briand III, P.E., is a senior geotechnical engineer for CDM Smith
who specializes in design, execution and construction of a wide variety of
deep foundation systems. He has over 9 years of experience on U.S.
projects for water, wastewater, industrial, commercial and federal clients.
Douglas J. Aghjayan, P.E., is a vice president for CDM Smith and
manages the northeast region of the geotechnical and tunnel engineering
services. He has over 30 years of experience in the design, execution and
construction of challenging geotechnical engineering projects and serves
as a subject matter expert for deep foundation design.
Michael S. Schultz, P.E., is a senior vice president for CDM Smith and
manages the geotechnical and tunnel engineering services division. He
has over 40 years of experience in the design, execution and construction
of complex geotechnical engineering projects and has published over 25
technical papers for geotechnical conferences and journals worldwide.
DEEP FOUNDATIONS * MAY/JUNE 2021 * 19
May/June 2021

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