Prediction of ground vibrations caused by pile driving: A new methodology

Estimates of ground motion generated during pile driving are usually made through empirical relationships and, more recently, using databases and expert systems. Vibration amplitudes, durations and waveforms, however, strongly depend on the geometry and the dynamic properties of the layers at a given site as well as the source characteristics. From previous results it seems difficult to predict vibrations in a proper way without knowing the main features of the site. The method proposed in this paper consists in determining the geometry and the dynamic characteristics of the geological layers by classical seismic tests, assuming that the structure is horizontally layered. On this basis, the propagation function of the site can be computed for any source point in the medium. The motion at the surface can then be obtained by convolution of the Green's function with the source function if this latter is known. As the energy transmission from the pile to the soil is very complex and in the plastic range, we propose to find an equivalent linear source function which is able to explain the main features of the recorded vibrations. This equivalent source function depends on the driving system and on the soil characteristics at the pile toe. This method has been successfully tested on one site, where different driving systems were used, and has been able to simulate waveforms and attenuation curves correctly for various penetration depths.