PREDICTION OF GROUND VIBRATIONS CAUSED BY PILE DRIVING - A NEW METHODOLOGY

Estimates of ground motion generated during pile driving are usually m ade through empirical relationships and, more recently, using database s and expert systems. Vibration amplitudes, durations and waveforms, h owever, 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 propose d in this paper consists in determining the geometry and the dynamic c haracteristics of the geological layers by classical seismic tests, as suming 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 convo lution 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 ver y complex and in the plastic range, we propose to find an equivalent l inear source function which is able to explain the main features of th e recorded vibrations. This equivalent source function depends on the driving system and on the soil characteristics at the pile toe. This m ethod has been successfully tested on one site, where different drivin g systems were used, and has been able to simulate waveforms and atten uation curves correctly for various penetration depths.