Torsional Piles in Two-Layered Nonhomogeneous Soil

Response of a pile subjected to torsional loading is significantly affected by soil profile. To investigate this characteristic, pile-soil interaction may be modeled by a series of independent springs distributed along the pile shaft (load transfer model). With this modeling, in this paper, analytical solutions are developed for the pile embedded in a two-layered soil profile. The soil stiffness of each layer is assumed to increase as a simple power law of depth, starting with any value at ground level. The solutions are expressed in terms of Bessel functions of noninteger order; and also presented in simplified expressions for some special cases. The solutions are verified using a spreadsheet, numerical program GASPILE, which is based on a nonlinear load transfer model. They are further collaborated using more rigorous numerical approaches available for a two-layered homogeneous soil. With the solutions, extensive parametric study was conducted and presented in nondimensional charts, in order to show consistency among these solutions, significant influence of stiffness profile on torsional response, and to identify conditions of utilizing these solutions. A case study is provided to illustrate the use of the current solutions, in particular for deducing soil modulus from torsional test results.