A Model of Undrained Stress-Strain Curves Considering Stress Path and Strain Softening

The stress path and strain-softening effect have a great influence on the strength and deformation of soils. Former test results show that the strength and deformation behaviors under lateral unloading conditions are quite different from those under axial loading conditions, especially for the structured soils. Based on the deformation mechanism of structured soils and incremental linear elasticity theory, a four-parameter stress-strain curve model is proposed by analyzing the stress-strain curves of axial loading and lateral unloading consolidated undrained shear tests. The model contains four important parameters: ultimate residual strength, curve shape factor, initial tangent modulus parameter, and peak strength parameter. All the parameters can be determined easily by conventional triaxial tests. Besides, comparisons of predicted and measured results of shear tests of different sands and soft soils indicate that the newly built model can describe the stress-strain curves with extensive adaptability and high accuracy, and it provides a unified nonlinear elastic model for both strain-hardening and strain-softening soils.