Prototype Piling in Soft Clay — A Case Study of Ground Vibrations: Field Measurement

Ground vibrations are generated either by natural phenomena or by human activities. Among the natural phenomena, earthquake is the principal source of ground vibrations of most interest. Ground vibrations generated by human activities are called manmade vibrations and these vary greatly in intensity depending on the particular source of vibration. The seismic waves associated with man-made vibrations propagate in the ground and inevitably interact with structures that are above-ground or underground. This interaction induces vibrations in the structure and, in extreme cases, affect its serviceability and integrity seriously. Still, there is no method to quantify the levels of piling vibration. Estimation of amplitudes and frequencies of vibration are based on experience and site testing. Therefore, in order to characterize the ground vibration due to piling, field measurement of ground vibration during prototype pile driving in soft clay was carried out. This paper presents the details of field measurement, instrumentation, collection of vibration data, acquisition and processing of data using PC-based data acquisition system made during the pile driving. The measurement of ground and already installed pile vibrations during prototype pile driving at a construction site in Chennai was carried out. The soil at this site is loose soft clay. The pile was of the type driven casing cast-in-situ pile of 500mm (OD) diameter. The depth of penetration of the pile was 13.25m. A 4 tonne hammer with a drop height of 1m drove the 25mm thick Mild Steel (MS) tube casing. During driving, ground acceleration was measured at a distance of 5D and 25D, where D is the diameter of pile, from the centre of pile. The vertical acceleration of an already installed pile situated at a distance of 37D from the driven pile were recorded. Piezoelectric acceleration transducers, power amplifiers, and tape recorder were used for the measurement. Acceleration signals were recorded using TEAC recorder. The recorded signals were processed using PC-based Data Acquisition System with DASYLAB software. The response time-histories and spectra of ground vibrations are presented and discussed