The design of a railway track substructure requires a realistic understanding of the resilient behavior of the underlying track foundation
materials, namely, the subballast and subgrade layers. Currently, the best available method of characterizing the resilient behavior of
track foundation materials is through the execution of cyclic triaxial tests, although these do not have the ability to impose principal stress
rotation (PSR) on test specimens. A previous paper by the authors demonstrated that PSR increases the rate of permanent strain development.
This paper reports on the effects of PSR on the resilient behavior of track foundation materials. Four different reconstituted soils selected to
represent typical track foundation materials were subjected to undrained cyclic and torsional shear tests in a hollow-cylinder apparatus. It
was established that PSR reduces the resilient modulus of the materials compared with cyclic loading without PSR. The effects of PSR as a function
of clay content, overconsolidation ratio (OCR), and consolidation regime (isotropic or anisotropic) were also investigated.