Theoretical analyses of load transfer mechanism for special pile foundations

In recent years, the special piles have been focused at home and abroad, including the piles with non-uniform cross-sectional area along shafts and those with special geometrical cross-sections. The load bearing capacity is enhanced for special piles by means of altering the pile geometry. Since many previous studies mainly emphasize on the bearing capacity, the complex fundamental load transfer mechanisms between special piles and their surrounding soil, called geometrical effects, are not well investigated and fully understood. Theoretical solutions are derive through equilibrium analyses for calculating the effective vertical stress, the unit positive (negative) shaft resistance, the total shaft resistance and the axial force (dragload). Those solutions are calibrated by reported large-scale model tests. The vertical shearing mechanisms of special piles are investigated by comparing a circular pile, an H-pile and an X-shaped pile with the same cross-sectional area. The geometrical effects are preliminarily discussed.