Stress relaxation coefficient and formulation for soft soils

Current studies rarely investigate the stress relaxation behaviour of soft soils. This paper proposes a practically useful coefficient with a formulation based on the behaviour of stress relaxation under onedimensional conditions. Firstly, the stress relaxation coefficient is proposed after summarising stress relaxation test results according to the linear relationship between the vertical stress and time in a double logarithmic plot. Secondly, from the newly developed rate-dependency based elastoviscoplastic formulations, an analytical solution for stress relaxation is derived. A unique relationship connecting the stress relaxation coefficient, the secondary compression coefficient and the ratedependency coefficient is then obtained. The applicability of the stress relaxation formulation with its key coefficient to determine time-dependent parameters is finally validated with published experimental results on reconstituted illite and Berthierville clay.