Piling in fine and medium sand—a case study of ground and pile vibration

Abstract

The paper presents the results of the measurement of ground and pile vibrations from a field investigation of prototype piling in which a steel casing of 600 mm diameter was driven in fine and medium sand for a depth of 16.4 m by impacting a hammer of mass 4100 kg dropped from a height of 2.4 m by a motorised winch fitted in a pile rig. In the case of ground vibration, both horizontal and vertical accelerations at 3 m, and vertical velocity at 15 m on the ground surface from the driven pile were measured. So also, vibration of the top of the already installed pile at 6.25 m from the driven pile was measured. Vibrations were measured using piezoelectric accelerometers and recorded using a 16-channel RT 145D DAT recorder. The recorded data were processed and acquired using DASYLAB data acquisition system. Time history plots of velocity and acceleration of ground were obtained. The maximum peak ground vertical velocity measured at a distance of 25 times the diameter of pile from the driven pile was 126.2 mm/s. The maximum vertical acceleration of the already installed pile situated at a distance of 10.42 times diameter of pile was 123.42 m/s 2 indicating the resonance of pile due to shock wave propagating in the soil medium. The time history of the ground vibration indicates its impulsive dynamic nature of short duration in contrast to the random periodic nature of ground waves generated by earthquake. Spectral analysis of the time histories of ground accelerations shows a dominant vertical frequency of 35.21 Hz and horizontal 25 Hz. The vertical frequency of pile was observed to be 25 Hz. Based on these spectral frequencies and going by the permissible vibration limits prescribed in various standards and codes, it has been found that the ground and pile vibrations were quite severe. Such severe ground vibration has got the potential of inflicting damage to structures in the vicinity. The problem can be quite serious in the midst of cluster of buildings in the urban habitat in the vicinity of pile driving.