EI 02C097
01 Jul 97
(c) Penetration resistance is dense, final submerged sand,
penetration resistance occurs with time after driving. Driving
inorganic silts or stiff, fissured, friable shale, or clay stone can
equipment and piles shall be selected with sufficient capacity to
dramatically increase during driving, apparently from dilation and
overcome driving resistance or driving periodically delayed to allow
reduced pore water pressure. A "relaxation" (decrease) in
pore water pressures to increse.
Table 6-2
Recommended Soil Parameters for Wave Equation (Copyright permission, Goble, Rausche, Likins and Associates, Inc. 1988)
Damping Constants Jc , seconds/ft (seconds/m)
Quake
, inches (mm)
u
Tip1
Soil
Skin
Tip
Skin
Cohesionless
0.05 (0.16)
0.15 (0.50)
0.10 (2.54)
Bb / 120
Cohesive
0.30 (0.90)
0.15 (0.50)
0.10 (2.54)
Bb / 120
Selected tip quake should not be less than 0.05 inch. Bb is the effective tip (base) diameter; pipe piles should be plugged.
1
(d) The pile shall be driven to a driving resistance that
(1) PDA equipment. PDA can be performed routinely in the
exceeds the ultimate pile capacity determined from results of
field following a schematic arrangement shown in Figure 6-2.
wave equation analysis or penetration resistance when
The system includes two strain transducers and two
relaxation is not considered. Driving stresses in the pile shall not
accelerometers bolted to the pile near its top, which feed data to
exceed allowable stress limits. Piles driven into soils with freeze
the pile driving analyzer equipment. The oscilloscope monitors
or relaxation effects should be restruck at a later time such as one
signals from the transducers and accelerometers to indicate data
or more days after driving to measure a more realistic
quality and to check for pile damage. The tape recorder stores
penetration resistance for design verification.
the data, while an optional plotter can plot data. Digital
computations of the data are controlled with a Motorola 68000
(e) Analysis of the bearing capacity and performance of the
microprocessor with output fed to a printer built into the pile
pile by wave equation analysis can be contested by the
driving analyzer. The printer also documents input and output
contractor and resolved at the contractor's expense through
selections.
resubmittals performed and sealed by a registered engineer. The
resubmittal should include field verification using driving and
(a) The strain transducers consist of four resistance foil
load tests, and any other methods approved by the Government
gauges attached in a full bridge.
design engineer.
(b) The piezoelectric accelerometers measure pile motion
b. Pile driving analysis. Improvements in electronic
and consist of a quartz crystal that produces a voltage
instruments permit the measurement of data for evaluating
proportional to the pressure caused by the accelerating pile
hammer and driving system performance, pile driving stresses,
mass.
structural integrity, and ultimate pile capacity. The required data
may be measured and pile performance evaluated in fractions of
(c) Data can be sent from the pile driving analyzer to other
a second after each hammer blow using pile driving analyzer
equipment such as a plotter, oscilloscope, strip chart recorder,
equipments. PDA is also useful when restriking piles after some
modem for transmitting data to a distant office or analysis center,
time following pile installation to determine the effects of freeze
and a computer. The computer can be used to analyze pile
or relaxation on pile performance. The Case method (Pile Buck,
performance by the Case and CAPWAPC methods.
Inc. 1988) developed at Case Institute of Technology (now Case
(2) Case Method. This method uses the force F (t) and
Western Reserve University) is the most widely used technique.
acceleration (t) measured at the pile top as a function of time
The CAPWAPC analytical method is also applied with results
during a hammer blow. The velocity v (t) is obtained by
of the PDA to calibrate the wave equation analysis and to lead to
reliable estimates of the ultimate static pile capacity provided soil
integrating the acceleration. The PDA and its transducers were
freeze, relaxation, or long-term changes in soil characteristics are
developed to obtain these data for the Case method.
considered. The CAPWAPC method quakes and damping
factors, and therefore, confirms input data required for the wave
equation analysis.
6-4
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