TORSION SHEAR TESTS ON CYCLIC STRESS-DILATANCY RELATIONSHIP OF SAND Sand

Habib Shahnazari and Ikuo Towhata

ABSTRACT: Several cyclic torsional drained simple shear tests were performed on Toyoura sand in order to investigate the stress-dilatancy relationship under large number of regular and irregular loading cycles. In particular, effects of different factors such as initial anisotropic stress state, initial confining pressure, density and shear history on this relationship were studied. It was found that the stress-dilatancy relationship changes suddenly after each loading reversal with a contractive behavior. When loading reversal occurs at a higher value of stress ratio, the more contractive behavior is observed after the reversal. Although the stress-dilatancy diagrams of different cycles start from different extent of contraction in irregular loading, they converge to a common one as stress loading continues. Test results showed that initial confining pressure and initial anisotropic stress state do not have any important effects on stress-dilatancy relationship. It was found that density and shear history affect the stress-dilatancy relation. Change of stress-dilatancy relationship due to increase of density or shear history leads to less contractive behavior. Results of this research provide complete and accurate information on the stress-dilatancy relationship under large number of regular or irregular cyclic loading and effects of different factors on this relationship. This information can be used in modeling of cyclic stress-dilatancy relations and volumetric strain. The investigated volume change and stress-dilatancy relationship in this study together with seepage analysis can predict the excess pore water pressure for liquefaction analysis.

Key words: constitutive eaupation of soils, dilatancy, drained shear, sand, torsion (IGC: D7)