Theoretical “t-z” Curves for Piles in Radially Inhomogeneous Soil-Article

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The paper develops simplified theoretical “t-z” curves for estimating settlement of axially loaded piles while accounting for soil disturbance caused by pile installation. Conventional curves often assume soil stiffness is uniform around the pile, although installation can soften nearby soil and increase predicted settlement.<br /><br />The authors combine a concentric-cylinder model of how shear stress decreases with distance from the pile, soil stress–strain relationships, and radial integration to calculate pile–soil interface settlement. They derive correction factors for radially inhomogeneous soil using linear and power-law stiffness profiles, and examine linear-elastic, power-law, and hyperbolic soil constitutive models.<br /><br />Comparisons show that a correction factor derived from the simpler linear-elastic model generally approximates more complex calculations well. For the cases studied, its differences from nonlinear-model results were typically below 10%; ignoring installation-related inhomogeneity produced substantially larger errors. A power-law stiffness profile also gave results close to the linear profile, with about a 2% settlement difference in the example considered.<br /><br />The proposed approach offers a practical way to incorporate installation effects into existing “t-z” curves using a small number of parameters. However, evidence for calibrating those parameters is limited, and the demonstration relies mainly on measurements from a Houston site involving bored piles in stiff clay. Further experimental and numerical work is needed to establish appropriate parameters for other soils and installation methods, especially driven piles.

Keywords

t-z curves

pile settlement

axially loaded piles

soil disturbance

pile installation

soil stiffness

radial inhomogeneity

correction factor

nonlinear soil model

driven piles