A modified strain rate dependent constitutive model for chalk and porous rock

Mohammad Reza Hajiabadi*, Hamidreza M. Nick

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


This paper modifies a 3D geomechanical constitutive model that uses two independent yield surfaces composed of shear failure and a strain rate-dependent pore collapse yield surfaces in order to describe the dilation and compaction mechanism of deformation. The model is developed based on the combination of non-associated shear failure and the viscoplastic consistency model relying on empirical formulation originally developed by J.A. de Waal and coworkers in the late 1980s. The model has the capability of representing the compaction deformation due to the creep phase. The model is also capable of predicting the softening in shear failure, which offers the option to use the model for stability analyses. A fully implicit stress-update algorithm for the multi-mechanism consistency model is used to determine the viscoplastic strain components. Several simulations are considered using a single element model in uniaxial and triaxial conditions to illustrate the behavior of the proposed model. Comparing the results with laboratory data indicates that the proposed model can reproduce the rate-dependent behavior in chalk.
Original languageEnglish
Article number104406
JournalInternational Journal of Rock Mechanics and Mining Sciences
Number of pages12
Publication statusPublished - 2020


  • Creep
  • Compaction
  • Dilation
  • Rate dependent
  • Viscoplastic
  • Chalk

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