Viscoplastic model for geologic materials with generalized flow rule

The general yield function in the hierarchical approach for constitutive modelling of materials is used with Perzyna's theory to characterize viscoplastic behaviour of geologic materials: a sand and rock salt. Particular attention is given to determination of the constants from laboratory quasistatic or short term, and creep tests. The proposed model is verified with respect to observed laboratory response of the sand and salt. It is implemented in a non‐linear finite element procedure and applied to analyse time‐dependent behaviour of a cavity in the rock salt.