Stress-Strain Behavior of Jointed Rock - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 54

Figure 3.9 One-dimensional stress-strain behavior of intact rock

To illustrate elastic-viscoplastic stress-strain behavior, the rheological model represent-
ed in Fig. 3.9 (lower right) may be used. This one-dimensional model is composed of a
spring, a so-called “Hooke element”, to describe elastic behavior, followed by a dashpot
and a sliding element, referred to as the “Newton element” and “Saint-Venant elem-
ent”, respectively. The latter are arranged in parallel to each other forming a so-called
“Bingham body”. The dashpot element describes delayed (viscoplastic) strain. The
sliding element consists of two blocks in contact with each other. They can only be dis-
placed relative to each other when the shear stress acting in the contact surface exceeds
σ cIR . The displacements at the sliding element and the resulting strains are irreversible.
According to the Mohr-Coulomb failure criterion, the residual unconfi ned compressive
strength σ cIR * can be expressed as with (3.21):

(3.33)

where c IR * and φ IR * are the residual values of cohesion and friction angle. In case of a

tensile failure the residual tensile strength σ tIR * can normally be assumed to be zero. In