Horizontal soil reaction of a cylindrical pile segment with a soft zone

An analytical solution in the realm of two-dimensional linear elasticity theory is presented for the soil reaction around a laterally loaded cylindrical pile segment surrounded by an annular zone of soft elastic material, under plane strain conditions. To this end, a seminal model is extended to account for different boundary conditions at the interfaces separating the annular zone from the pile and the outer material. Analytical closed-form solutions are derived for the stiffness of the system and the stress and strain fields in the annular zone, for the following combinations of shear boundary conditions: (1) perfectly bonded interfaces, (2) perfectly smooth interfaces, (3) perfectly bonded inner and perfectly smooth outer interface, and (4) perfectly smooth inner and perfectly bonded outer interface. It is shown that for both very thin and very thick soft zones, the stiffness of the system becomes independent of shear boundary conditions. The predictions of the model are compared against those of two models based on strength-of-materials theory. Three-dimensional effects and numerical simulation aspects are discussed.