Evolution of radial stresses in direct simple shear testing: integration of principal stress rotation theory and SANISAND constitutive modeling

This investigation presents a comprehensive analysis of radial stress evolution during Direct Simple Shear (DSS) testing through the integration of principal stress rotation theory and advanced constitutive modeling. The study addresses a fundamental limitation in DSS testing: the inability to directly measure radial stresses during shearing. Two complementary approaches are implemented to investigate this phenomenon. First, a theoretical framework based on principal stress rotation demonstrates distinct evolution patterns between loose (φ = 33°) and dense (φ = 37°) sands, revealing that radial stresses can exceed vertical confining pressure in dense configurations. Second, the implementation of the SANISAND constitutive model validates these findings while extending the analysis to both monotonic and cyclic loading conditions. The model successfully captures sophisticated aspects of sand behavior, including the exceedance of vertical confining pressure by radial stresses while maintaining constant volume conditions. This dual approach provides unprecedented insights into stress evolution mechanisms during DSS testing, challenging traditional assumptions and establishing a robust framework for analyzing granular material behavior under simple shear conditions. The findings have significant implications for geotechnical engineering practice, particularly in applications involving cyclic loading and density-dependent soil response.