Ground vibration measurements with special reference to pile driving
There has been increased concern in recent years over the level and nature of the ground vibrations. The importance of such vibration has increased rapidly due to developments in construction in urban areas, where the effects of ground borne vibration on both humans and structures are considerable. Research has been undertaken to improve techniques used in the measurements, analyses and evaluation of ground vibrations caused by rail and road traffic, blasting and in particular those generated from pile driving activities. The amplitude of the vibration caused by the pile driving operation is a function of pile type, hammer type and the ground conditions. In order to investigate the effects of these three variables, a large number of visits were made to different sites which provided a range of different driving conditions. The main requirements in the analysis of the vibrations measured include vibration amplitude and their relevant frequency. The vibration amplitude is usually expressed in term of peak particle acceleration, velocity or displacement. In this work, the ground vibration is measured in terms of peak particle velocity using velocity transducers (geophone). In order to evaluate the true peak particle resultant velocity, the three components of the ground vibration are measured simultaneously by three orthogonally positioned sets of geophone. Recording the vibration data is achieved by employing a portable digital recorder which digitizes the analogue signals recieved from the transducers and stores the captured data on standard floppy disks for further analysis. The results are presented in tables and diagrams and detailed comments are given in the discussion of the recorded data. Some methods of analyses are reviewed and two new methods are proposed. These proposed methods include the application of the hemispherical projection technique in interpreting and displaying the three dimesional vibration information into a two dimensional plane. The other method analysed the attenuation of the ground vibration according to the arrival time of the generated waves from the pile toe and along the ground surface. It is suggested that when the arrival times of these two wave fronts coincide at one particular point, a highest vibration amplitude may be expected at that poinL The effect of ground vibration on building is investigated in large scale test in Aitwick where the dynamic strain of purpose built L-shape walls are recorded during driving steel sheet and H-pile at different stand-off from the walls using a winch-drop-hammer and a vibrodriver.