Research on the modification of structured Cam Clay model based on triaxial undrained effective stress path

Both laboratory and in situ tests and engineering practice 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 consolidated undrained triaxial test of structured clay, two improvements were made to the structured Cam Clay (SCC) model: (1) The formula for calculating the additional void ratio Δe was modified, which can accurately simulate the effective stress path of 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 was used to simulate the confined compression test, the consolidated undrained and drained triaxial tests of structured clay. The calculation results were compared with the experimental results and the calculation results of the SCC model. The results show that the MSCC model can better simulate the triaxial undrained effective stress path and stress-strain curves of confined compression and consolidated drained triaxial tests of structured clay. Finally, the sensitivity analyses of parameters β (plastic deformation parameter in yield surface), p'yi (initial structural yield stress), Δei (initial additional void ratio), b (structure degradation rate), γ (shear-induced structure degradation parameter) and ω (reflecting the influence of soil structure on plastic flow criterion) in the MSCC model were carried out. The results show that parameter β affected the effective stress path in the yield surface of structured clay, parameter p'yi affected peak strength, parameter Δei affected residual strength, parameters b and γ affected strength degradation rate after the peak value, and parameter ω affected the magnitude of deviatoric strain when strength began to degrade.