01 July 1997
For a vibratory hammer to be suitable for a particular application, the dynamic
force should suit the equation
Fdyn $ i ($o@Rso+$i@Rsi+$t@Rt)/R
= dynamic force of vibrator, kN
beta factor for soil resistance (general)
beta factor for soil resistance (outside shaft)
beta factor for soil resistance (inside shaft)
beta factor for soil resistance (toe)
inside pile shaft soil resistance, kN
= outside pile shaft soil resistance, kN
pile toe soil resistance, kN.
pile factor (0.8 for concrete piling and 1 for all other piling.)
soil resilience coefficient (should be between 0.6 and 0.8 for vibration
frequencies between 5 and 10 Hz and 1 for all other frequencies.)
Suggested values for $ are given in table 2-2. The toe resistance and the outside and
inside (where applicable with open ended pipe and cylinder pile) shaft resistance should
be computed using methods similar to those employed for impact hammers. For
extraction, this formula is altered to read
Fdyn $ i ($o Rso+$i Rsi+$t Rt)/R-Fext
Fext = extraction force of crane, kN.
Once this is known, a possible vibratory hammer for the job should be selected
based on minimum permissible dynamic force in kN. The parameter of dynamic mass
(the dynamic mass includes any mass of the vibrator not dampened from vibration, the
clamp and any mass of the pile) should be noted, along with the frequency and eccentric
moment of the machine.
Next the basic parameters of the vibratory hammer/pile system must be checked.
The first is the peak acceleration, whose value is computed using the equation
n = 102 Fdyn / Mdyn
n = peak acceleration, g's.
Mdyn = dynamic mass of system, kg
Minimum values for this acceleration are given in table 2-3.
Figure 2-2a. Method for Sizing Vibratory Hammers, Metric Units.