Bearing capacity of under-reamed piles in clay using lower bound finite element limit analysis

ABSTRACT In this study, bearing capacity of under-reamed piles in non-homogeneous clay is estimated numerically. A detailed parametric study is carried out for different length to shaft diameter ratio (Lu /D), bulb position (hb /Du ), under-ream angle (β) and constant m indicating the increase of undrained cohesion, number of bulbs (nb ), bulb spacing (s) and pile–soil adhesion factor (αs ). The bearing capacity of the under-reamed pile is presented through design charts and expressed by a dimensionless factor Ncu. Ncu increases significantly with increases in nb, Lu /D and m and moderately with increases in β and αs . For m > 0, Ncu decreases moderately with the increase in hb /Du . For two bulbs, m > 0, the optimum bulb spacing is found at 1.25–1.75Du . For one bulb, Ncu increases in the range of 67.52–162.84% than the pile without bulb. For two bulbs, Ncu increases in the range of 129.41–250.40% than the pile without bulb.