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Constitutive modeling of rock materials considering the void compaction characteristics

100%

Xie S. , Han Z. , Chen Y. , Wang Y. , Zhao Y. , Lin H.

tom Vol. 22, no. 2

art. no. e60, 1--15

The study of constitutive model is of great significance to engineering safety evaluation and geological disaster prevention. In this paper, rock materials were regarded as a composite geological material composed of voids and rock matrix, and then a piecewise constitutive model bounded by the yield point was proposed. It can reflect the complete stress–strain curves of rocks, including the compaction stage, the elastic stage, the plastic yield stage and the post-peak stage. Primarily, an objective method to determine the yield point based on the stress difference was proposed. For the rock deformation before yielding, the relationship between the strain of rock materials and the strains of voids and rock matrix was analyzed to establish the corresponding constitutive model. Subsequently, based on the modified Weibull distribution, a damage statistical constitutive model of rocks was established to describe the nonlinear deformation after the yield point. Meanwhile, the determining method of model parameters was given. Finally, the uniaxial and triaxial compression test data of different types of rocks were used to verify the proposed model. The results indicate that the model curves are in good agreement with the experimental results. Hence, it is feasible and reasonable to divide the macroscopic strain of rocks into the strains of voids and rock matrix. Additionally, there is a power function attenuation relationship between the deformation ratio of voids to rock matrix and the axial stress.

Statistical damage constitutive model based on the Hoek-Brown criterion

100%

Chen Y. , Lin H. , Wang Y. , Xie S. , Zhao Y. , Yong W.

tom Vol. 21, no. 3

556--564

The constitutive models of rock are essentially the general depictions of the mechanical responses of rock mass under complex geological environments. Statistical distribution-based constitutive models are of great efficacy in reflecting the rock failure process and the stress–strain relation from the perspective of damage, while most of which were achieved by adopting Drucker–Prager criterion or Mohr–Coulomb criterion to characterize microelement failure. In this study, underpinned by Hoek–Brown strength criterion and damage theory, a new statistical damage constitutive model, which is simple in terms of model expression and capable of reflecting the strain softening characteristics of rock in post-peak stage, was established. First, the rock in the failure process was divided into infinite microelements including elastic part satisfying Hooke’s law and damaged part retaining residual strength. Based on strain equivalence hypothesis, the relation between rock microelement strength and damage variable was derived. By assuming the statistical law of microelement strength obeying Weibull distribution and the microelement failure conforming to Hoek–Brown criterion, the new statistical damage constitutive model based on Hoek–Brown criterion was, therefore, gained. The mathematical expressions of the corresponding model parameters were subsequently deduced in accordance with the geometric characteristics of the deviatoric stress–strain curve. Last, the existing conventional triaxial compression test data of representative rock samples under different confining stresses were employed to compare with the theoretical curves by proposed model, the consistency between which was quantified by utilizing the correlation factor evaluation method. The result indicated that the proposed model could well describe the entire stress–strain relationship of rock failure process and manifest the characteristics of rock residual strength. It is of great significance to the researches on rock damage and softening issues and rock reinforcement treatments.