IFCEE 2021
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The Driven Pile at IFCEE 2021
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IFCEE 2021 PDCA E.A.L. SMITH AWARD LECTURE
Presentation Topic: The 70-Year-Old Wave Equation Analysis
of Pile Driving is Still Young and Dynamic
Presenter: Dr. Frank Rausche, GRL Engineers, Inc.
When E.A.L. Smith was asked by his employer, Raymond Concrete
Pile Company, to calculate stresses in their highly non-uniform
step tapered piles during pile driving, he had to come up with a
practical analysis tool. At the time in the late 1940s, electronic
computers were only in the early development stage and what
Smith initially came up with was something that only civil engineering
graduate students could be asked to do: cranking the
mechanical calculators. However, Smith was soon able to program
an early IBM mainframe computer with a numerical solution to
the one-dimensional wave equation. Not too long after Smith’s
initial work, routine dynamic measurements and real-time data
interpretation methods developed at Case Institute of Technology
helped pile driving professionals understand and verify the wave
equation-calculated blow counts and stresses. Together with more
user-friendly and powerful computers, these developments made
possible worldwide acceptance of Smith’s method.
For a widespread dissemination of the method, it was necessary
to put Smith’s algorithm into a user-friendly computer program,
which would be rigorously checked against both electronic
measurements such as provided by Pile Driving Analyzer® (PDA)
and static loading tests. The Federal Highway Administration
(FHWA) recognized the power of dynamic measurement and
analysis tools and sponsored the development of the Wave
Equation Analysis of Pile Driving (WEAP) program about 45 years
ago. The FHWA also required developing a detailed diesel hammer
model, non-linear cushion treatment, performance checks
of all hammer types and a review and expansion of Smith’s recommended
soil resistance parameters.
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The acceptance of WEAP was widespread; however, continuous
program maintenance was needed, first going from mainframe
computers with punched card data input to personal
computers and eventually the Microsoft Windows environment.
These requirements and the need to respond to additional user
demands led to the development of the proprietary GRLWEAP
program by Pile Dynamics, Inc. Indeed, users expected options
that went far beyond the original Bearing Graph calculation, for
example, Inspector’s Charts and Driveability Analyses, Residual
Stress Analysis, Static Resistance to Driving (SRD) determination
by Setup Factor and later Friction Fatigue, a vibratory hammer
model, Frequency of Stress Extrema tables for Pile Fatigue Damage
assessment, Static Bending of inclined piles, two-pile and two-toe
modeling as well as numerous Static Soil Resistance and CPT
based analysis routines.
Certainly, finite element analysis models exist that are more
sophisticated than Smith’s approach. However, they require soil
data, which are generally unavailable for routine construction
preparation and construction control and they lack the simplicity
and experience base that wave equation users enjoy. Also, the
development of the wave equation method does not stop; incorporation
of new knowledge from academic work, field measurements
and construction site experiences occurs continuously.
PDCA’s members, contractors, engineers and equipment suppliers
have been and are a critical help in furthering the technology.
Also important is PDCA’s sponsorship of regular educational
events to update and improve users’ skills and member’s knowledge
for a proper application of modern measurement and analysis
methods, in general, and the wave equation, in particular. This
presentation is an expression of PDCA’s continued education
efforts discussing the historic, current and future developments
and applications of dynamic pile analysis methods, their benefits
and challenges.
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