Study on damage evolution of intact and jointed marble subjected to cyclic true triaxial loading

Coal–rock dynamic disasters seriously threaten safe production in coal mines, and an effective early warning is especially important to reduce the losses caused by these disasters. The occurrence of coal–rock dynamic disasters is determined by mining-induced stress loading and unloading. Therefore, it is of great significance to analyze the precursory information of coal deformation and failure during true triaxial stress loading and unloading. In this study, the deformation and failure of coal samples subjected to true triaxial loading and unloading, including fixed axial stress and unloading confining stress (FASUCS), are experimentally investigated. Meanwhile, acoustic emission (AE) during the deformation of coal samples is monitored, and the multi-fractal characteristics of AE are analyzed. Furthermore, combined with the deformation and failure of coal samples, the precursory information of coal deformation and rupture during true triaxial stress loading and unloading is obtained. Finally, the relationship between multi-fractal characteristics and damage evolution of coal samples under FASUCS is discussed. The results show that the multi-fractal spectral widths of AE time series under the conditions of FASUCS with different initial confining stresses or unloading rates are quite different, but the dynamic changes of multi-fractal parameters [Formula: see text] and [Formula: see text] are similar. This indicates that the microscopic complexity of AE events of coal samples under different conditions of FASUCS differs, but the macroscopic generation mechanism of AE events has inherent uniformity. The dynamic changes of [Formula: see text] and [Formula: see text] can reflect the stress and damage degree of coal samples. The dynamic change process of [Formula: see text] well accords with the damage evolution process of coal samples. A gradual decrease of [Formula: see text] corresponds to a slow increase of damage, while a sharp increase of it corresponds to a rapid growth of damage. At the same time, the mutation point of damage curve at distinct stress difference levels shares the same variation trend with the [Formula: see text] mutation point. The change of [Formula: see text] can reflect the damage process of coal samples, which can be used as precursor information for predicting coal–rock rupture. The finding is of great significance for the early warning of coal–rock dynamic disasters.

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The effect of stress state factor on fracture of sandstones under true triaxial loading

International Journal of Fracture ◽

10.1007/s10704-008-9214-6 ◽

2008 ◽

Vol 149 (1) ◽

pp. 1-10 ◽

Cited By ~ 13

Author(s):

A. D. Alexeev ◽

V. N. Revva ◽

L. L. Bachurin ◽

I. Y. Prokhorov

Keyword(s):

Stress State ◽

Triaxial Loading ◽

True Triaxial ◽

State Factor

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Research on Coal Mechanical Properties Based on True Triaxial Loading and Unloading Experiment

Advances in Civil Engineering ◽

10.1155/2021/6675222 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Yanyan Peng ◽

Haoxiang Deng ◽

Minghong Xing ◽

Pengfei Guo ◽

Chun Zhu

Keyword(s):

Mechanical Properties ◽

Acoustic Emission ◽

Principal Stress ◽

Coal Mine ◽

Test System ◽

Intermediate Principal Stress ◽

Mine Safety ◽

Triaxial Loading ◽

True Triaxial ◽

Loading And Unloading

To study the safety issues caused by coal mine excavation, self-developed simulation of earth interior atmosphere and sound test system was used to perform true triaxial loading and unloading tests of coal. An acoustic emission detection system was used to record the damage evolution trend of coal under different intermediate principal stress states. The experimental results show that in the true triaxial unloading test, as the intermediate principal stress increases, the failure state of coal changes from shear failure to partial shear tension failure, finally leading to overall yield failure. In the stress-strain curves, with the increase in intermediate principal stress, the strain in the direction of intermediate principal stress gradually changes from compression to expansion, and typical expansion occurs. The Mogi–Coulomb strength criterion better reflects the strength failure characteristics of coal during unloading. The stress-acoustic emission diagrams show that the increase in intermediate principal stress causes the internal cracks of the coal to grow unsteadily and exponentially, and the increase in intermediate principal stress makes the coal lose its ability to continue to bear the load. Studying the influence of the intermediate principal stress on the mechanical properties of coal has practical significance for coal mine safety production.

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Study on Damage Evolution Model of Sandstone under Triaxial Loading and Postpeak Unloading Considering Nonlinear Behaviors

Geofluids ◽

10.1155/2021/2395789 ◽

2021 ◽

Vol 2021 ◽

pp. 1-17

Author(s):

Tianbai Zhou ◽

Yueping Qin ◽

Jian Cheng ◽

Xiaoyu Zhang ◽

Qiufeng Ma

Keyword(s):

Damage Evolution ◽

Energy Balance Equation ◽

Stress Strain ◽

Triaxial Loading ◽

Nonlinear Properties ◽

Confining Pressures ◽

Strain Relationship ◽

Loading And Unloading ◽

Nonlinear Behaviors ◽

Initial Compaction

Conventional triaxial loading and unloading tests were carried out on sandstone samples in the Zigong area, of Sichuan Province, China. The changes in the elastic modulus of the unloading curves under different confining pressures were calculated, and the evolution law of the nonlinear properties of rock was analyzed. The results show that the rock is subjected to nonlinear damage during initial compaction, the elastic phase, destruction, and postpeak unloading. Moreover, the nonlinear behaviors of rock are restrained by the confining pressures. On this basis, a nonlinear stress-strain relationship affected by the average stress is proposed to describe nonlinear behaviors in the initial compaction stage. According to the test data, the evolution laws of various energies inside the rock during loading and unloading cycles are obtained. The results show that the external work is transformed into elastic energy and damage dissipated energy. Based on the energy analysis, the energy balance equation is established according to the law of energy conservation. By deriving the energy balance equation, the damage evolution equation of sandstone under triaxial loading is solved to establish a continuous constitutive model. The calculation results of the model are compared with the test results from two aspects of loading and postpeak unloading. The comparison results show that the proposed model, which reflects the whole stress-strain process and nonlinear properties of rock, could also describe the stress-strain relationship at the postpeak unloading stage to some extent.

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