ABSTRACT:

An elasto-plastic-creep material model is developed for modeling the faihu'e of geo-materiais. The plastic and creep strains are accounted for through the strain decomposition technique. The DmckerPrager yield function is used to model the failure of the material. The incremental creep strain is assumed to develop in the direction of the deviatoric stress only. The model is implemented in the finite element program ADINA and is verified through a numerical example. Comparison of the numerical result with the analytical one indicates the correctness of the model.

INTRODUCTION'

While the creep behavior of rocksalt has been extensively studied (Munson, 1997), the fxacturing (and eventual failure) of rocksalt has received much less attention. Rocksalt subjected to low strain rates demonstrates viscoplastic behavior. Under higher strain rates rocksalt shows brittle behavior. In the latter case, micro fractures develop at the grain scale and evolve into visible fractures.

Extensive observations and measurements from the underground excavations at the Waste Isolation Pilot Plant (WIPP), together with a reliable finite elementool, can be used to study the fracture and failure of rocksalt. The incorporation of the failure process into the computer models results in a more comprehensive and realistic assessment of the behavior of the rock mass, which, in turn, enhances mine safety and economics. To this end, the formulation of an elasto-plastic-crccp material model and its implementation in the finite element program ADINA arc presented. The plastic behavior of the material is modeled using the Drucker-Prager yield criterion. The creep behavior is modeled using the WIPP reference creep law. The model is verified through a numerical example. Comparison of the numerical result with the analytical one indicates the correctness of the model.

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