Dynamic behaviour of laterally loaded model piles in clay

Dynamic experiments in lateral mode were carried out on model aluminium single piles in a simulated elastic half-space filled with clay soil to determine dynamic constants of the soil-pile system and to study the bending behaviour of piles. Model piles with various lengths were subjected to steady-state harmonic vibrations with different magnitudes of force of 7-30 N applied over a wide range of frequencies from 2 Hz to 50 Hz. The load transferred to the pile, pile head displacement and strain gauge readings at different locations on the pile were measured. It is observed consistently that the magnitude of the applied force and the pile length significantly affect the natural frequency of the soil-pile system. It is found that rigid piles behave linearly even at the higher magnitudes of applied force, but that flexible piles behave non-linearly as the magnitude of the applied force increases, which leads to a substantial reduction of the lateral stiffness of the soil-pile system. Damping of the soil-pile system is found to increase with an increase in pile length and magnitude of the applied force, owing to the occurrence of radiation and hysteretic damping. Based on experiments carried out on model piles embedded in clay at low confining pressure, it is found that the maximum dynamic bending moment of long flexible piles is about four times higher than that of short rigid piles. The maximum bending moment under dynamic loads occurs at deeper depth than the corresponding depth for static loads, which indicates an increase of the active length of piles under dynamic load.