# Two Papers on Vibratory and Impact-Vibration Hammers

We present two papers on these topics, one first presented last year and one which has just been completed.

## Inclusion of Rotational Inertial Effects in Power Consumption Calculations for Vibratory Pile Equipment

Abstract: Virtually all treatments of power consumption and modelled performance for vibratory pile driving equipment assume a constant rotational speed of the eccentrics. In reality this is not possible due to the inertial effects of the eccentrics themselves and the necessity that, without inertia, the power output of the motor for the eccentrics must follow the instantaneous power requirements, which continuously vary. In this paper the rotational inertial effects of the eccentrics are included in the calculations. Because of the non-linear nature of the equations, a numerical model was developed to estimate the dimensionless torque required to turn the eccentrics at a target rotational speed. The results track closely with those of the continuous torque model described by Warrington (2006) for a wide variety of inertia/eccentric moment ratios, although there are exceptional cases if the peak acceleration is increased and the frequency decreased. As an excursus, the method of computing the inertia/eccentric moment ratio and its corresponding pendulum frequency is described in detail for those who can apply this to other problems.

## Development of a Parametric Model for the Simulation of Impact-Vibration Pile Driving Equipment

Abstract: Impact-vibration pile driving equipment has been an important part of vibratory pile driving equipment since the early years of development. In the 1960’s the VNIIstroidormash institute in Moscow developed a series of impact-vibration hammers; however, the development of these hammers was stopped in favour of the diesel hammers. The emergence of the need to convert construction equipment to electric power due to environmental considerations reopens the possibility that these hammers may once again need to be considered to drive piles, as the original impact-vibration hammers (in common with their early vibratory counterparts) were powered using specialised electric motors. A model is first developed to simulate the mechanical working of these hammers, followed by comparison to actual designs. The results are generally in line with the original tests (to the extent the results are known) but variances are noted and discussed. Some suggestions for forward movement on the design of this equipment are set forth.