Dynamic modulus degradation for soft saturated clay under coupling stress paths of cyclic deviatoric stress and cyclic confining pressure

The dynamic modulus is always the most important parameter in soil dynamics, and the most popular equivalent linear constitutive model in geotechnical engineering is just to quantitatively describe the dynamic modulus degradation. In the previous researches on the dynamic modulus, the factors such as OCR, PI, soil fabric, saturation degree, stress history, frequency and aging have been considered. However, because of some reasons, the stress path, especially the coupling stress path of cyclic deviatoric stress and cyclic confining pressure, has rarely been studied. Considering the fact that the cyclic confining pressure is ubiquitous in soil stress fields, the influences of the cyclic confining pressure on the dynamic modulus of soft saturated clays are studied based on the step-by-step tests. The test results show that the confining pressure changes the magnitudes of the dynamic modulus under certain dynamic strains, and the changing tendency and magnitudes are related to the phase differences. The Hardin-Drnevich model is also proved not to fit the behavior of the dynamic modulus degradation, while the Stokoe equation is more appropriate.