Time-dependent deformation behaviors of weak sandstones

L. S. Tsai, Y. M. Hsieh, Meng-Chia Weng, T. H. Huang, F. S. Jeng*

*Corresponding author for this work

Research output: Contribution to journalArticle

84 Scopus citations


Time-dependent deformation behavior of rocks has a significant impact on the stability of rock slopes or underground constructions. This paper presents systematic experimental data regarding time-dependent deformation of a typical weak sandstone, known as the Mushan sandstone. The observed deformations are further separated to distinguish elastic and viscoplastic behaviors of the weak sandstone through the use of multi-staged loading-creep-unloading-reloading tests. The stress path is designed to be a purely hydrostatic loading followed by a pure shear, so that the deformations induced by these two types of stresses can be distinguished. For elastic behavior, although the nonlinear stress-strain relations vary according to the applied hydrostatic stress, these stress-strain relations can be normalized by the applied hydrostatic stress or the bulk modulus and converted into a single consistent stress-strain curve. Inelastic behavior is then obtained by subtracting the elastic deformation from the total deformation. As a result, the characteristics of the viscoplastic deformation are that: (1) the direction of the viscoplastic flow is time independent, and (2) it has a similar direction to the conventionally defined plastic flow. As such, the viscoplastic potential has a similar shape to the plastic potential, but the size of the former changes with time, while the latter has a size that is time independent. Meanwhile, through the calculation of irreversible work, direct evidence of orthogonality between the yield surface and the plastic flow, as well as the viscoplastic flow, is observed. Thus, it is reasonable to assert that the yield surface, the plastic potential, and the viscoplastic potential all have the same geometry. Consequently, the associated flow rules are applicable to modeling the time-dependent deformational behavior of weak sandstones.

Original languageEnglish
Pages (from-to)144-154
Number of pages11
JournalInternational Journal of Rock Mechanics and Mining Sciences
Issue number2
StatePublished - 1 Feb 2008


  • Associated flow rule
  • Creep
  • Plastic potential surface
  • Time dependent
  • Viscoplastic potential surface
  • Weak sandstone
  • Yield surface

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