TORSIONAL PILES IN NONHOMOGENEOUS MEDIA

The torsional response of a pile exhibits features which are a mixture of those for axial and lateral response. Ar low load levels, the resp onse is dominated by interaction with the upper soil layers and by the pile rigidity itself, similar to laterally loaded piles. However, fai lure will generally occur by the whole pile twisting, and so the latte r part of the response incorporates the integrated effect of all soil penetrated by the pile, as is the case for axial loading. In view of t he above, solutions for the torsional response of pile must endeavour to incorporate accurate modelling of the sail stiffness profile, and a lso pay appropriate attention to the gradual development of slip (rela tive twist) between pile and soil. The paper presents analytical and n umerical solutions for the torsional response of piles embedded in non -homogeneous soil, where the stiffness profile follows a simple power law with depth. The solutions encompass: (I) vertical non-homogeneity of soil expressed as a power law; (2) non-linear soil response, modell ed using a hyperbolic stress-strain law; (3) effect of relative slip b etween pile and soil for non-homogeneous stiffness and limiting shaft friction; (4) expressions for the critical pile slenderness ratio (or length) beyond which the pile head response becomes independent of the pile length. The solutions are developed using a load transfer approa ch, with each soil layer acting independently from neighbouring layers , and are expressed in terms of Bessel functions of non-integer order, and as simple non-dimensionalised charts. The solutions are applied t o two well-documented case histories in the latter part of the paper. Copyright (C) 1996 Elsevier Science Ltd.