Axial behaviour of bored pile foundations

Technical Abstract

Nine bored pile foundations, each nominally 0.75m diameter by 5.5m deep, were constructed in a deposit of loose gravel above the water table. Four of the piles were loaded monotonically to failure in uplift while the remaining five were subjected to 30 cycles of 1Hz sine wave loading at various amplitudes prior to being failed in uplift. The uplift capacity and stiffness of the cyclically loaded piles was compared with that of the monotonically loaded piles. At low levels of cyclic loading (less than 60 percent of uplift capacity) the pile response was largely elastic with no significant degradation in stiffness. At higher levels, the pile response was highly inelastic and non-linear with a large reduction in load-displacement stiffness (by a factor of up to 16.1). These results are in general agreement with an equivalent study carried out at model scale in the laboratory, providing evidence that such model studies may be useful in predicting prototype response to cyclic loading. Recommendations for practice are made.