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Modelling Rheological Behaviour of RockAbstract:Mechanical models seem to be particularly appropriate for describing the material behavior of rock both phenomenologically and numerically. For this purpose the basic Hookean and Newtonian elements as well as a modified St. Venant element, whose deformability is determined by two strength limits (peak and residual) and a nonassociated flow rule, are employed. Analogous to the viscoelastic case, a general loading shall be split up into its spherical and deviatoric stress components. Different material models are assigned to these components. To treat the modified St. Venant elements, which are dependent upon the general state of stress, a coupling of these material models is introduced. Models composed of several elements are handled in a way strictly related to the individual elements, i.e. the behavior of these elements is governed solely by the force acting in the element. Thereby and due to the constant material parameters the criteria for loading and unloading are simply and uniquely given, even for complicated models. Further, strain hardening and softening or cyclic loading can be handled, without, as in standard plasticity analysis, having to expand or shift the yield surfaces in stress space. With the help of simple model structures it is discussed, how various fundamental rock properties  e.g. complete stressstrain curves, hysteresis, timedependent deformations  can be represented in a simple manner. An example from rock mechanics practice illustrates how big the significance of certain features may be, e.g. volume dilatancy, contained implicitly in the theoretical formulations. Authors:Fritz, PitIndex Terms:FEM; rhelogy; material properties; rock; TunnelingGroup; analysisFurther Information:Date published: 1982 
