Strength Characteristics and Double-Yield Elastoplastic Constitutive Model of Granite

We characterized the strength and deformability of Wuyi granite based on Brazilian tests and axisymmetric compression tests under different confining pressures (0, 5, 10, 20, 25, and 30 MPa). Facilitated by a modified three-dimensional (3D) Hoek-Brown strength criterion, the 3D strength envelopes of the granite in the principal stress space were established based only on axisymmetric compression tests, allowing exploring the 3D nonlinear strength characteristics. In the framework of generalized plasticity, an elastoplastic constitutive model based on the Hoek-Brown strength criterion was proposed to depict the nonlinear mechanical behavior of the granite. In the constitutive model, two parabolic yield surfaces, together with two corresponding non-associated flow rules, were incorporated to honor the shear and volumetric dilatancy mechanisms of the granite, respectively. The proposed constitutive model was then compared with the experimental results via the return mapping algorithm. The excellent agreement between the numerical and experimental results indicates that the proposed double-yield elastoplastic constitutive model can capture the mechanical behavior of the granite well.