AbstractIn a previous paper it was established with very simple assumptions that piles might undergo a directional instability during placement, of a type more usually found in aerodynamic problems. The study is here extended to piles driven into soils whose shear strength and lateral reaction modulus can vary with depth. The analysis consists of a parametric study of the effect of linear variation of the soil parameters with depth on the critical lengths for instability, and a comparison of site evidence with the critical lengths obtained from a stepwise‐constant representation of the variation of soil parameters with depth. The theory is shown to give very reasonable estimates of the depths at which major deviation starts, although there is a pressingneed for more detailed site and laboratory dat