Triaxial Compression Testing at Constant and Reducing Confining Pressure for the Mechanical Characterization of a Specific Type of Sandstone

Zhang, Jiu-chang; Lin, Zhengzhong; Dong, Bo; Guo, Ran

doi:10.1007/s00603-020-02357-z

Cited by 15 publications

(5 citation statements)

References 23 publications

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“…The fracture angle was predicted to stabilize at approximately 45 • . The fracture morphology and orientation of the rock specimen exhibited the same strong graduality and continuity with confining pressure as the experimental results [46][47][48], which cannot be achieved by the conventional damage model [45].…”

Section: Fracture Modessupporting

confidence: 50%

An Anisotropic Damage Model of Quasi-Brittle Materials and Its Application to the Fracture Process Simulation

et al. 2022

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Accurate predictions of the failure behaviors of quasi-brittle materials are of practical significance to underground engineering. In this work, a novel anisotropic damage model is proposed based on continuous damage mechanics. The anisotropic damage model includes a two-parameter parabolic-type failure criterion, a stiffness degradation model that considers anisotropic damage, and damage evolution equations for tension and shear, respectively. The advantage of this model is that the degradation of elastic stiffness only occurs in the direction parallel to the failure surface for shear damage, avoiding the interpenetration of crack surfaces. In addition, the shear damage evolution equation is established based on the equivalent shear strain on the failure face. A cyclic iterative method based on the proposed anisotropic damage model was developed to numerically simulate the fracture process of quasi-brittle materials. The developed model and method are important because the ready-made finite element software is difficult to simulate the anisotropic damage of quasi-brittle materials. The proposed anisotropic damage model was tested against a conventional damage model and validated against two benchmark experiments: uniaxial and biaxial compression tests and Brazilian splitting tests. The results demonstrate that the proposed anisotropic damage model simulates the mesoscale damage mode, macroscale fracture modes, and strength characteristics more effectively and accurately than conventional damage models.

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Section: Fracture Modessupporting

confidence: 50%

An Anisotropic Damage Model of Quasi-Brittle Materials and Its Application to the Fracture Process Simulation

et al. 2022

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“…Moreover, the higher the confining pressure, the more obvious the observed ductility characteristics are. Peisen Zhang [24] et al conducted seepage tests on sandstone with different confining pressure and cyclic load and confirmed the five evolution stages of sandstone, including the primary microfracture compression closure stage, the elastic compression stage, the crack stability development stage, the crack rapid development stage, and the post-peak deformation failure stage. The authors pointed out that rock cracking stress and damage stress are important indicators for determining the rock failure process.…”

Section: Introductionmentioning

confidence: 93%

Research on the Response Mechanism of Coal Rock Mass under Stress and Pressure

Shan

Lai

et al. 2023

Materials

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In this paper, the strength and deformation failure characteristics of bearing coal rock mass are related to the confining pressure, and the SAS-2000 experimental system is used to carry out uniaxial and 3, 6, and 9 MPa triaxial tests on coal rock to assess the strength and deformation failure characteristics of coal rock under different confining pressure conditions. The results show that the stress–strain curve of coal rock undergoes four evolutionary stages after fracture: compaction, elasticity, plasticity, and rupture. With confining pressure, the peak strength of coal rock increases, and the elastic modulus increases nonlinearly. The coal sample changes more with confining pressure, and the elastic modulus is generally smaller than that of fine sandstone. The stage of evolution under confining pressure constitutes the failure process of coal rock, with the stress of different evolution stages causing various degrees of damage to coal rock. In the initial compaction stage, the unique pore structure of the coal sample makes the confining pressure effect more apparent; the confining pressure makes the bearing capacity of the coal rock plastic stage stronger, the residual strength of the coal sample has a linear relationship with the confining pressure, and the residual strength of the fine sandstone has a nonlinear relationship with the confining pressure. Changing the confining pressure state will cause the two kinds of coal rock samples to change from brittle failure to plastic failure. Different coal rocks under uniaxial compression experience more brittle failure, and the overall degree of crushing is higher. The coal sample in the triaxial state experiences predominantly ductile fracture. The whole is relatively complete after failure as a shear failure occurs. The fine sandstone specimen experiences brittle failure. The degree of failure is low, and the confining pressure’s effect on the coal sample is obvious.

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“…The crack initiation stress ( ci ) identified by these two methods shows great consistency. After that, the unstable crack growth stress was reached (which is named the crack damage stress, cd ), and at this point the volumetric strain started to reverse (from compassion to dilation) (Vásárhelyi and Bobet 2000;Zhang et al 2021b). This stage was noted as the crack damage stage, which was characterised by a drop in ultrasonic wave velocity, intensified plastic deformation, the boost of AE events, and damage initiation (will be discussed in Sects.…”

Section: Stress-strain Curves and Yielding Surfacementioning

confidence: 99%

“…The effect of hydrostatic pressure is normally ignored in the associated plastic flow, for example, as model assumptions in the von Mises yield criterion. Recent research shows that the associated plastic flow rule can roughly estimate the plasticity of rock specimens (Zhang et al 2021a). However, as a typical frictional material, the plastic behaviour of rock is related to the slip of microcracks (shear failures), where the increment of plastic strain generally does not coincide with the gradient of plastic yield function (Lockner et al 1992;Li et al 2017;Oh et al 2017).…”

Section: Introductionmentioning

confidence: 99%

A Pre-peak Elastoplastic Damage Model of Gosford Sandstone Based on Acoustic Emission and Ultrasonic Wave Measurement

et al. 2022

Rock Mech Rock Eng

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The determination of internal material damage is always an arduous challenge. Non-destructive monitoring methods show great potential in quantitatively determining the internal material properties, whereas most of the studies relying on external observations remain in a qualitative stage. They either violate the basic thermodynamic assumptions or are difficult to guide engineering practice. In this paper, following the theory of continuum mechanics, an elastoplastic damage model based on non-destructive monitoring methods (i.e., acoustic emission and ultrasonic wave velocity measurement) has been developed. To capture the continuous and precise damage evolution inside rock mass, P wave velocity obtained by ultrasonic wave measurement was utilised and then considered as an input for the proposed elastoplastic damage model. Triaxial loading test results on six Gosford sandstone samples were analysed first to characterise critical stresses along the stress–strain loading curves, such as crack closure stress, stable crack propagation stress and unstable crack propagation stress. The drop of ultrasonic wave velocity can be seen as an indicator to represent the damage evolution inside rock material. Damage initiation is also closely related to the confining stress and dilation induced volumetric expansion. The test results also suggested that the Drucker–Prager criterion is sufficient to describe the plastic yielding surface and the following material hardening. A non-associated plastic flow assumption was adopted, considering the essence of microcrack shearing in rock failure and the effect of hydrostatic pressure on plastic deformation. A modified Drucker–Prager plastic potential was also introduced to track the orientation of plastic increment with material hardening. A scalar damage variable was derived from ultrasonic wave measurement results to indirectly represent the deterioration of rock properties (modulus). The proposed model was used to match lab test results with high consistency, and the main features of rock behaviour in triaxial loading tests were successfully captured by the model. Finally, the damage evolution of rock samples was analysed, which indicates that damage is dependent on its conjugate force, namely damage energy release rate Y. This study proves that P wave velocity can be an effective approach to measure and forecast the internal damage evolution inside rock mass, which has broad prospects for engineering applications.

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Triaxial Compression Testing at Constant and Reducing Confining Pressure for the Mechanical Characterization of a Specific Type of Sandstone

Cited by 15 publications

References 23 publications

An Anisotropic Damage Model of Quasi-Brittle Materials and Its Application to the Fracture Process Simulation

An Anisotropic Damage Model of Quasi-Brittle Materials and Its Application to the Fracture Process Simulation

Research on the Response Mechanism of Coal Rock Mass under Stress and Pressure

A Pre-peak Elastoplastic Damage Model of Gosford Sandstone Based on Acoustic Emission and Ultrasonic Wave Measurement

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