Thermodynamic constitutive model for anisotropic undrained shear strength of saturated clays

An approach is proposed for the undrained strength anisotropy of saturated clays based on a thermodynamic constitutive model, TTM (Tsinghua thermodynamic soil model). The model analyses and experiments indicate that the anisotropic consolidation or K₀ consolidation can be an important cause for the strength anisotropy of geotechnical materials, and the strength anisotropy becomes more significant with the decrease of the consolidation stress ratio K_c. During the undrained loading, the direction of the principal stresses has a huge influence on the undrained strength and deformation of soils. Generally speaking, with the rotation of principal stresses from 0°to 90°, the undrained shear strength decreases while the peak strain increases. Besides, the anisotropic consolidation causes the non-coaxiality of the principal stresses and strains. Based on the proposed model, simulations and predictions are made for various test results of Kaolin clay and Boston blue clay, which indicate that TTM is able to show and predict the strength change and deformation behavior of soils under complex stress paths caused by the strength anisotropy, strain softening and rotation of direction of the principal axis of stress.