A simple model for geo-materials involving shear-induced anisotropic degradation

When geo-materials, such as soil, gravelly soil and soft rocks, are loaded by shear stress, they frequently exhibit volumetric deformation, either dilation or compression, that cannot be modeled by conventional elasticity of isotropic material. This study aims, using as few parameters as possible, to develop a material model designed to simulate the main deformation of geo-materials. A constitutive model based on the concept of shear-induced anisotropic degradation is proposed. The proposed constitutive model is characterized by the following features: (1) significant shear-induced volumetric deformation prior to failure, (2) modulus stiffening under hydrostatic loading and degradation under shearing; (3) stress-induced anisotropy; and (4) being versatile in representing many geo-materials and their behaviors under various stress paths. In the proposed model, the deformational moduli, E, G, and G ', vary according to stress state. The stiffening and degradation of these moduli render the deformational behavior of geo-materials. The proposed model needs only six material parameters, all of which possess physical meaning and can be easily obtained. Finally, the versatility of the proposed model is demonstrated by simulating various geo-materials such as sandstone, gravelly soil and shale loaded under different stress paths.