Estimation of pile capacity in hard
PWR considering the maximum
design load = NDR is an overly
conservative approach that can result
in unnecessarily large pile sizes.
• Pile Hammers - new / refurbished
TECHNICAL
• Custom Leads - all tubular, pinned style, boom point, fair
leads, fixed / swinging, onshore / offshore
• Accessories - drive caps, cushion material, air line oilers,
air hose, replacement parts
• Sales and rentals of pile driving equipment
• Repair and service of pile driving equipment
Phone: 706-398-1178
Fax: 706-398-1188
www.vulcanhammer.com
6. Conclusion
From the PDA tests and CAPWAP analyses
presented in Section 5, it can be
concluded that:
1. The geotechnical capacity can exceed
the MFSR and NDR in hard PWR without
exceeding the maximum allowable
compressive stress and without
damaging the pile. Therefore, pile sizes
can be estimated based on estimated
maximum factored structural strength
limit state and MFSR data in the predesign
phase (bidding phase) or in the
design phase when no load test data is
available.
2. According to AASHTO article 10.7.3.2.2
(Piles Driven to Soft Rock), “soft rock
that can be penetrated by pile driving
shall be treated in the same manner as
soil for the purpose of design for bearing
resistance in accordance with article
10.7.3.8.” It seems the word “penetrated”
does not clearly explain what soft
rock is; in our opinion, combining this
statement with penetration resistance
(N values) would characterize the soft
rock better. If we assume upper layers
of PWR with 100 ≤ N ≤ 50/5" can belong
to the class of soft rock, then, from
these test results, PWR with 50/5" ≤ N
≤ 50/1" should be considered hard or
practical refusal medium.
3. Estimation of pile capacity in hard
PWR considering the maximum
design load = NDR is an overly conservative
approach that can result in
unnecessarily large pile sizes. 3) As
a result of applying jdyn to MFSLSL,
two load factors are actually applied
to the MFSLSL which seems too
conservative. If we treat the response
of hard PWR very similar to the
response of rock, then, structural
strength limit state conditions of the
steel section should control the design
in hard PWR; considering NDR for
design seems redundant.
4. Therefore, the NDR calculated using
equation 1 is probably not necessary
when piles are tipped in hard PWR
that can be considered practical refusal
materials. From the perception of wave
mechanics, the hard PWR appears to
present a free end condition; velocity
of stress wave doubles and force diminishes
to zero – a condition evoked
by bedrock. Therefore, the estimation
of NDR in drivable soil layers should
be probably considered in the light of
soil dynamics.
5. Modeling of hard PWR in static pile
capacity calculation should follow the
same approach as hard rock, i.e., use
unit weight, and cohesion (c) instead of
unit and friction angle (j) that are commonly
used in silty sand, sand and sandy
silt layers in APILE – FHWA Method.
6. More research needs to be conducted
for modeling the capacity of PWR
with N values ranging from N=100 to
N=50/1" using laboratory test results
for unit weight, cohesion, friction
angle, etc. The laboratory test results
can also help us understand better
characteristics of both soft and hard
PWR in combination with N values. t
www.piledrivers.org PILEDRIVER | 125
/www.vulcanhammer.com
/www.piledrivers.org
