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

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 (L-u/D), bulb position (h(b)/D-u), under-ream angle (beta) and constant m indicating the increase of undrained cohesion, number of bulbs (n(b)), bulb spacing (s) and pile-soil adhesion factor (a(s)). The bearing capacity of the under-reamed pile is presented through design charts and expressed by a dimensionless factor N-cu. N-cu increases significantly with increases in n(b), L-u/D and m and moderately with increases in beta and a(s). For m > 0, N-cu decreases moderately with the increase in h(b)/D-u. For two bulbs, m > 0, the optimum bulb spacing is found at 1.25-1.75D(u). For one bulb, N-cu increases in the range of 67.52-162.84% than the pile without bulb. For two bulbs, N-cu increases in the range of 129.41-250.40% than the pile without bulb.