TY - JOUR

T1 - Time-dependent deformation behaviors of weak sandstones

AU - Tsai, L. S.

AU - Hsieh, Y. M.

AU - Weng, Meng-Chia

AU - Huang, T. H.

AU - Jeng, F. S.

PY - 2008/2

Y1 - 2008/2

N2 - 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.

AB - 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.

KW - Associated flow rule

KW - Creep

KW - Plastic potential surface

KW - Time dependent

KW - Viscoplastic potential surface

KW - Weak sandstone

KW - Yield surface

UR - http://www.scopus.com/inward/record.url?scp=38149092461&partnerID=8YFLogxK

U2 - 10.1016/j.ijrmms.2007.04.008

DO - 10.1016/j.ijrmms.2007.04.008

M3 - Article

AN - SCOPUS:38149092461

SN - 1365-1609

VL - 45

SP - 144

EP - 154

JO - International Journal of Rock Mechanics and Mining Sciences

JF - International Journal of Rock Mechanics and Mining Sciences

IS - 2

ER -