Abstract
Based on the concept of generalized plasticity, this study proposes a constitutive model to describe the time-dependent behavior and wetting deterioration of sandstone. The proposed model (1) exhibits nonlinear elasticity under hydrostatic and shear loading, (2) follows the associated flow rule for viscoplastic deformation, (3) adopts a creep modulus that varies with the stress ratio, (4) considers the primary and secondary creep behaviors of rock, and (5) considers the effect of wetting deterioration. This model requires 13 material parameters, comprising 3 for elasticity, 7 for plasticity, and 3 for creep. All parameters can be determined easily by following the suggested procedures. The proposed model is first validated by comparison with triaxial tests of sandstone under different hydrostatic stress and cyclic loading conditions. In addition, the model is versatile in simulating time-dependent behavior through a series of multistage creep tests. Finally, to consider the effects of wetting deterioration, triaxial and creep tests under dry and water-saturated conditions are simulated. Comparison of the simulated and experimental data shows that the proposed model can predict the behavior of sandstone in dry and saturated conditions.
Highlights
The theory of generalized plasticity was first introduced by Zienkiewicz and Mroz (1984) to simulate soil behavior and was later elaborated by Pastor and Zienkiewicz (1986) and Pastor et al (1990)
The associated flow rules are applicable for modeling the time-dependent deformational behavior of sandstone. Based on these characteristics of sandstone, this study extends the work of Weng and Ling (2012) to develop an elastic–viscoplastic model that incorporates the generalized plasticity concept
This study extends previous research on predicting the time-dependent behavior and wetting deterioration of sandstone and presents a constitutive model based on nonlinear elasticity and generalized plasticity
Summary
The theory of generalized plasticity was first introduced by Zienkiewicz and Mroz (1984) to simulate soil behavior and was later elaborated by Pastor and Zienkiewicz (1986) and Pastor et al (1990). The associated flow rules are applicable for modeling the time-dependent deformational behavior of sandstone Based on these characteristics of sandstone, this study extends the work of Weng and Ling (2012) to develop an elastic–viscoplastic model that incorporates the generalized plasticity concept. : dr represents instantaneous deformation, whereas the second term ðnc dr corresponds to long-term deformation, including the primary and secondary creep behavior of the rock Based on this concept of generalized plasticity, the yield and viscoplastic potential surfaces are not directly specified, but the scalar functions for plastic modulus HL=U, creep modulus Hc, and direction tensors n, ng, and nc are required. To incorporate the deformation characteristics of sandstone into the generalized plasticity, this study proposes (and subsequently defines) the major constituents of the model, including nonlinear elasticity, dilatancy, plastic modulus, and a time-dependent function
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