Abstract
Pile foundations are used when surface soil is unsuitable for shallow foundations and the load that transfers to the ground is very high. Conventional bored cast in situ piles with bentonite were accepted as the most reliable piling system for most of the projects. Chiselling hammers with varying weights are used for advancing boreholes having different diameter of piles. The chiselling action produces low energy compared to precast pile driving. But this low energy, even causes problems because of proximity of structures to the construction site. Energy is directly imparted to the soil during the chiselling operations by dropping the chisel into the borehole, creating stress waves. In the present study, ground vibration measurements are conducted in a model study of boring operation for direct mud circulation (DMC) type of piling. Ground vibration analyses were carried out for two different soil profiles with hard and soft stratum. The intensity of vibrations produced during impact loading at different distances and depths from the source of vibration were measured on layered soft clay and lateritic soil mediums with accelerometers connected to data acquisition system. Variation of the vertical acceleration was found to comply with the previous studies. From the pattern of the horizontal acceleration, and also the material damping coefficients calculated at different depths, gave an idea about the material through which the wave propagates. With the scaled energy used in the present study the rate of attenuation and peak particle velocity for unit distance is calculated. From this the peak particle velocity can be calculated for higher hammer energies which are used in real DMC method of piling. Finally a method is suggested to predict the probable ground vibrations that produced during piling by using accelerometers and auxiliary boreholes at the time of site investigation using a modified SPT setup for any type of soil profiles.
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