EI 02G001
CEMP-E
01 July 1997
If the peak acceleration figure is too low, a vibratory with a higher dynamic force must be
chosen and the peak acceleration recalculated. This iteration must continue until the
peak acceleration value is achieved.
(4) Next, the required amplitude of the vibratory system is computed using the equation
A = 2 K y / Wdyn
where A = total cycle displacement amplitude, inches
K = eccentric moment, inch-pounds
The preferred amplitude values are shown in table 2-4b; combinations of pile, soil, and
frequency in shaded boxes show cases where the pile should not be vibrated at the given
frequency range and soil condition. Larger amplitudes than those shown are generally
permissible.
If the amplitude is insufficient, then a new vibratory hammer with the same or greater
dynamic force as the previous one and greater eccentric moment should be chosen and
the amplitude checked again.
(5) Finally, the peak velocity should be checked; it is computed by the equation
vdyn = 307.24 n/rounds per minute
where
vdyn
=
peak dynamic velocity of vibrating system, feet per second; should
fall between 1.7 and 2.6 feet per second, but it can be higher if
necessary.
RPM =
frequency of vibrations, rev/min
It should be kept in mind that method presented here is at best a very sophisticated "rule
of thumb" and should be supplemented by local experience with both actual piles and
soils and good engineering judgment. One item not considered here is the static weight
of the system; this can be increased by mounting bias weights on top of the vibratory
hammer. This can increase the speed of pile penetration.
Figure 2-2b. (Concluded)
2-12
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