Modification of structured Cam-clay model based on triaxial undrained effective stress path

Both laboratory and in-situ tests and engineering practices show that naturally sedimented clays have a specific structure. Therefore, establishing a structural constitutive model is of great significance in accurate predicting the mechanical responses of natural clays and solving practical geotechnical engineering problems. Firstly, based on the effective stress path of the consolidated undrained triaxial tests on structured clay, two improvements are made to the structured Cam-clay (SCC) model: (1) The formula for calculating the additional void ratio Δe is modified, which can accurately simulate the effective stress path of the structured clay beyond the critical state line. (2) Considering the plasticity in the yield surface, i.e., subyielding characteristic, the effective stress path in the yield surface can be well simulated. Then, the modified structured Cam-clay (MSCC) model is used to simulate the confined compression tests, the consolidated undrained and drained triaxial tests on the structured clay. The calculated results are compared with the experimental ones and those by the SCC model. The results show that the MSCC model can better simulate the triaxial undrained effective stress path and stress-strain curves of the confined compression and consolidated drained triaxial tests on the structured clay. Finally, the sensitivity analyses of parameters β (plastic deformation parameter in yield surface), p'_yi (initial structural yield stress), Δe_i (initial additional void ratio), b (structure degradation rate), γ (shear-induced structure degradation parameter) and ω (reflecting the influences of soil structure on plastic flow criterion) in the MSCC model are carried out. The results show that parameter β affects the effective stress path in the yield surface of structured clay, parameter p'_yi affects peak strength, parameter Δe_i affects the residual strength, parameters b and $\gamma$ affect the strength degradation rate after the peak value, and parameter ω affects the magnitude of deviatoric strain when the strength begins to degrade.