Repetitive load testing: reversal or rotation

Permanent way support systems (roads, airfields, railways) subject to moving load, soil deposits subject to earthquakes, and soil beneath offshore structures subject to wave loading are classical examples of field situations where the soils will experience varying degrees of principal stress rotation. To assess the effects of this principal stress rotation, comparisons were made between the responses of a dry sand when subjected to stress-controlled repetitive triaxial and repetitive simple shear testing. Based on findings from this test program, an attempt was made to analyse the deformation response of a model footing simulating the railway field situation.Principal stress rotation was shown to be a major factor influencing the behaviour of dry granular material when subjected to repetitive load, the effect of which was to induce permanent deformation while the elastic response remained unchanged. The applicability of repetitive triaxial and repetitive simple shear testing in these circumstances is shown to be complex, and rational design methods for field situations involving repetitive loads have been reevaluated. Key words: principal stress rotation, repetitive load, repeated load, cyclic load, granular, triaxial test, simple shear test.