Abstract: The yield function of the conventional egg-shaped yield surface constitutive model can pass through the negative semi-axis of the-plane. It is commonly used to describe the mechanical properties of remolded soil or weakly cemented soil, but it cannot accurately reflect the structure of intact soft clay and its strength and deformation mechanism under the action of external loads. Based on this, the paper adopts the method of expanding the egg-shaped yield surface to represent the strength increase brought about by the internal arrangement of the soil forming a certain structure. Establish the relationship among the egg-shaped yield surface parameterwhich controls the degree of cementation, the structural expansion coefficientand the plastic cumulative strain. Describe the process of structural attenuation of the soil under the action of external loads by means of the kinematic hardening rule. Propose an egg-shaped yield surface elastoplastic constitutive model for structurally saturated soft clay. Give the method for determining the parameters. Compare the test results of the structurally saturated soft clay with the simulated values of this model to verify the rationality. Analyze the influence of structural parameters on the compression characteristics and triaxial undrained shear characteristics of the soil. This model can describe the characteristics of structured soil such as compression, stress development, strain hardening, and strain softening.

Key words: structured saturated soft clay, egg-shaped yield surface constitutive model, structural attenuation, strain softening