Effects of scour-hole depth on the bearing and uplift capacities of under-reamed pile in clay

Scouring causes reduction in the load-carrying capacity of pile foundation. The load-carrying capacity of a pile foundation can be increased by increasing the pile dimension. In the present study, under-reamed piles are considered under scour condition. In this study, bearing and uplift capacities of under-reamed pile in clay under scour condition are obtained numerically using lower bound finite element limit analysis. The effects of scour hole shape, bulb shape, and embedment ratio are studied. The non-dimensional bearing capacity factor (N-cus) and uplift capacity factor (F-cus) are presented through design charts. N-cus and F-cus of under-reamed pile are found to be significantly higher than those of pile without bulb under scour condition. N-cus and F-cus are found to decrease significantly with scour depth. N-cus and F-cus are found to increase with the increase in under-ream angle (beta). From the axial force distributions, it is found that bulb carries a significant portion of the ultimate load in axial compression and tension. With the consideration of stress history, bearing and uplift capacities of under-reamed pile are found to reduce significantly. Also, the extent of plastic shear failure in the soil is found to increase with decrease in scour depth and increase in embedment ratio.