Displacement Ductility Capacity Assessment for a Fixed-Head Pile in Cohesionless Soil

This study develops assessment formulas for the displacement ductility capacity of a fixed-head pile in cohesionless soils. The derivations of the formulas are based on an ideal model of a semiinfinite nonlinear pile in a Gibson soil, whose subgrade reaction modulus increases linearly with depth, to link the displacement ductility capacity of the pile with the pile–soil system parameters. The parameters in the formulas include the sectional overstrength ratio and curvature ductility capacity, as well as a modification factor for considering soil nonlinearity. The modification factor is a function of the displacement ratio of the pile’s ultimate displacement to the effective soil yield displacement, which is constructed through a number of numerical pushover analyses. The format of the formulas is similar to that for a pile in cohesive soils. For the case of linear soil, the formulas provide a lower-bound estimate of pile ductility capacity; the displacement ductility capacity of a pile in cohesionless soils is larger than that in cohesive soils. For the case of nonlinear soil, the modification factor for soil nonlinearity in cohesionless soils (the American Petroleum Institute sand $p\text{-}y$ model) is smaller than in cohesive soils (the Matlock clay $p\text{-}y$ model).