BEHAVIOUR OF SHORT PILE UNDER MACHINE INDUCED HORIZONTAL VIBRATIONS

Abstract

Short rigid piles are widely used to support structures such as wind turbines, traffic signals, jetties, transmission towers, highway overhead signs and water front structures. In order to assess the effect of L/D ratio and strain on short piles subjected to horizontal sinusoidal vibrations. Four RCC short piles of diameter 20cm, 30cm, 40cm and 50cm each having a length of 2m were cast The important part of this dynamic analysis is to calculate the stiffness and the damping ratio. For a better understanding of the site geotechnical properties of the site were also evaluated. To generate horizontal sinusoidal vibrations a motor-oscillator assembly was used. Four foundation bolts were cast into the pile cap to enable the mounting of a motoroscillator assembly. Three acceleration transducers were suitably mounted on the vertical face of the pile cap to monitor the induced accelerations. These piles have been tested for four different force level i.e. eccentricity setting of motor-oscillator assembly For each pile and eccentricity setting, acceleration-frequency records were analysed to obtain resonant frequency of the soil-pile system and shear strain at ground level. Using this data, a procedure has been developed to obtain damping ratio and stiffness of the soil-pile system. Conclusions have been drawn relating (i) Exciting force level and resonant frequency, (ii) Soil-pile stiffness and strain level and (iii) System damping and strain level, considering each pile individually. The influence of L/D ratio on the dynamic response of the soil-pile system has also been demonstrated.