Numerical Simulations of Laboratory Experiments for Determining the Post-yielding Mechanical Parameters of Soil and Rock

ABSTRACT: The mechanical parameters of constitutive equations for soil and rock can be determined by laboratory experiments in which a cylindrical specimen is commonly tested under uniaxial and triaxial compressive conditions. The distribution of stress in the specimen during the tests must be kept uniform and homogeneous. In this paper, numerical simulations are carried out to determine the distribution of stress in cylindrical and hollow cylindrical specimens under a uniaxial compressive state and the distribution of stress in a rectangular parallelepiped specimen under a plane strain condition. The results of the numerical simulations reveal that if cylindrical and hollow cylindrical specimens are tested under a uniaxial compressive condition, the stress distribution will no longer be uniform or homogeneous after the peak strength under strain-hardening and/or strain-softening conditions. This means that the post-yielding mechanical parameters of constitutive equations cannot be determined by cylindrical or hollow cylindrical specimens. On the other hand, if a rectangular parallelepiped specimen is tested under a plane strain condition, it is found that the stress distribution in the specimen will always be uniform and homogeneous, even after the peak strength. Thus, a rectangular pararellepiped specimen, compressed under a plane strain condition, is preferable for determining the post-yielding mechanical parameters of constitutive equations.