May/June 2021 - 18

dead load reaction force on a single pile, this would have had
additional costs associated with the dead load and the added
time to mobilize between test pile locations.
The most cost-effective solution for pile load testing in the
industry is the dynamic pile load test, which does not require
the added reaction pile installation of static load testing, or
the explosives needed for statnamic load testing. The factor of
safety for dynamic pile load testing is typically 2.0, based on
the 2015 International Building Code (2015 IBC). However,
this code, as amended by the Commonwealth of Massachusetts,
requires a factor of safety of 2.5 for dynamic pile load
testing because it is an indirect measurement of the pile load
as opposed to the direct load measurement available with
static or statnamic pile load testing methods. Because of the
higher factor of safety and unknowns associated with the
existing piles, it was determined that dynamic pile load
testing would be used in combination with the statnamic pile
load tests in case the larger required loads damaged the
65-year-old piles.
Novel Statnamic Load Testing
The statnamic pile load test, performed by Applied
Foundation Testing as a subconsultant to Geosciences Testing
and Research (dynamic load testing contractor) for this
project, is a specialized pile load test that few firms perform
nationally. This load testing method is more expensive than a
typical load test because it uses an impulse force (typically an
explosive device) that propels a mass upwards with an equal
and opposite reaction downward on the pile. Because the load
test is routinely used as an alternative to static pile load
testing and is a direct force measurement, the factor of safety
for the statnamic load testing is permitted to be 2.0 per the IBC
code. The statnamic load test setup is extremely compact,
involving a mobile test frame that is faster to set up and
execute than a static pile load test, and does not require
reaction piles or a dead load reaction. Additionally, the
reaction masses can be used to conduct dynamic pile load
tests in leiu of mobilizing a crane and pile driving hammer.
Thus, it was determined that a two-phase pile load testing
program would be conducted for this project. The pile load
testing locations were selected based on the existing test boring
data and the pile tip elevation plan. The program goal was to
test a wide cross section of pile lengths and pile embedments to
bracket potential pile capacities across the pier.
Phase 1 of the pile load testing program would determine
whether the project was financially feasible. The Phase 1
work was limited in scope to prevent the client from spending
unnecessary funds should the load testing not achieve the
required loads. This phase consisted of dynamic and
statnamic load testing on two piles at two load intervals (of
200 and 240 kips [890 and 1,068 kN]).
18 * DEEP FOUNDATIONS * MAY/JUNE 2021
Phase 2 of the pile load testing program further evaluated
existing pile capacities across varying pile lengths and
embedment depths. It also determined whether additional
foundation cost savings could be achieved that would make
the project more profitable for the owner and developer. The
Phase 2 program consisted of statnamic testing on 2 piles and
dynamic load testing on 10 piles.
Prior to performing pile load testing, low strain integrity
testing was performed using the sonic echo method (SEM) to
confirm whether any significant defects were present in the
piles and to determine the approximate installed pile lengths.
The SEM records indicated that no significant defects were
present in the piles below the mudline, and 10 of the 14 piles
demonstrated toe reflections that corresponded to the
approximate existing pile tip elevation from the as-built plan;
the four other pile test results were inconclusive with regard
to pile tip elevation.
Pile dynamic analyzer (PDA) measurements were
performed on each of the test piles during dynamic load
testing. Dynamic measurements recorded by the PDA
consisted of attaching strain transducers and accelerometers
near the top of the pile and converting the
Statnamic load test setup, with the reaction masses (larger blue) below the yellow
silencer and locking ring.
May/June 2021

Table of Contents for the Digital Edition of May/June 2021
