Abstract: Traditional plastic dilatancy models are based on coaxial plastic flow rule when describing relations between the stress ratio and plastic strain increment, in which stress-dilatancy behavior of soil only depends on stress ratio. A large number of test results show that the stress and strain are non-coaxial during plastic flow under complex stress conditions involving principal stress rotation; so the non-coaxiality cannot be ignored when analyzing stress-dilatancy behavior of soil. In order to investigate the effects of non-coaxiality on the stress-dilatancy behavior of sand under complex stress conditions involving principal stress axes rotation, a series of fixed principal stress axes shear tests and pure principal stress rotation tests and combined loading tests are conducted on the saturated sand using a hollow cylinder apparatus. The test results indicate that the stress-strain non-coaxiality would result in the deviation between the stress-dilatancy curves and Rowe-line under different stress paths, which can be modified through the Gutiereez’s modified dilatancy equation by introducing a non-coaxiality factor. In this way, Rowe’s stress-dilatancy equation can be made more applicable to loadings involving principal axes stress rotation.

Key words: stress-dilatancy, non-coaxiality, principal stress axes rotation, stress ratio