Ground vibrations caused by impact pile driving

Abstract

The limitations of energy-based vibration attenuation relationships are reviewed. The large scatter of reported results can be explained by the fact that such correlations do not take into account important dynamic pile and soil parameters. The propagation of driving energy from the hammer into the pile and from the pile to the soil along the shaft and at the base is discussed, using wave propagation theory. The importance of the impact velocity, the pile and soil impedance and of the distribution of the dynamic soil resistance are highlighted. The dynamic soil resistance, which depends on the strain-dependent impedance, is the source of ground vibrations. Guidance is given regarding the selection of soil impedance values, taking into account the strain-softening effect. Vibration propagation from the base and along the shaft can be calculated using analytical methods, which take into account the transfer of driving energy. Massarsch, K. R., 2005. Ground Vibrations Caused by Impact Pile Driving. Invited Lecture, Proceedings, Environmental Vibrations: Prediction, Monitoring, Mitigation and Evaluation (ISEV 2005). Okayama University, Japan, 20 – 22. September 2005. Taylor & Francis. Pp. 369 – 379. The following main aspects of vibration propagation during the driving of piles with an impact hammer can be identified: (A) – Wave propagation in the pile: the energy generated by the drop hammer (1) impacts the pile cap and the pile head (2) and the vibration energy is transmitted through the pile (3); (B) – Pile-soil interaction: along the pile shaft (4) and at the pile base (5); (C) – Wave propagation in the ground: transmission of vibrations through soil layers and the ground water; (D) – Dynamic soil structure interaction: dynamic response of buildings and installations in the building. The dynamic soil-structure interaction of piled foundations at small strains is described extensively in the literature, such as the dynamic response of machine foundations (Novak & Janes, 1989). However, little information is available regarding the dynamic pile-soil interaction during driving at large strain levels (Massarsch, 1992). Most investigations, which address vibrations caused by pile driving, discuss the propagation of vibrations in the ground and the response of buildings subjected to vibrations but do not consider the conditions at the source, i.e. the transfer of driving energy from the pile to the soil. Therefore, in this paper emphasis is placed on the discussion of parameters which govern the propagation of waves in the pile (A) and the dynamic pile-soil interaction (B), Figure 1. 1.1 Energy-based Vibration Attenuation Most investigations reporting measurements of ground vibrations from pile driving have adopted concepts which were developed for the case of vibrations due to rock blasting. The vibration intensity at a distance from the source is assumed to be a function of the energy released at the source. Attewell & Farmer (1973) analysed results of vibration measurements in different ground conditions and for different pile types. They came to the conclusion that the attenuation of ground vibration amplitude with distance from a pile is largely independent (!) of the geotechnical nature of the ground. They suggested that a conservative estimate of vibration velocity v at distance r from the energy source (pile) can be made from the following equation