Applying the statistical damage theory based on the Weibull distribution to describe rock deformation and failure processes is an important development in rock mechanics. The shape parameter of the Weibull distribution, m, determines the basic shape of the distribution curve; additionally, it also represents a physical characteristic which can be applied when constructing rock constitutive models. To study the evolution of m during rock failure when applying the Weibull distribution to rock mechanics, uniaxial cyclic loading tests of shale specimens were conducted and previous rock mechanics experiments under different temperatures and loading rates were reviewed. The results indicate that m varied with the accumulation of damage but was almost constant between the volume expansion point and the peak strength point of each specimen. Combined with previous studies about the accelerated failure behavior of rocks, we conclude that between the volume expansion point and the peak strength point, the mechanical behavior of the rock fracture process did not change significantly. Based on the characteristics of m at different damage stages during the rock failure process, ranges of m values at different damage stages are proposed. The conclusions reached in this study may be used as an important reference for theoretical research on rock mechanics.
It is clear that evaluating the fracturing effect with laboratory tests can shed some light on designing fracturing programs for shale gas exploitation. To evaluate the fracturing effect quantitatively, a series of uniaxial cyclic loading tests on shale were conducted. Based on the experimental results, a damage variable derived from the total axial strains of the loading–unloading cycles was established and introduced into a damage evolution equation to analyze damage evolution in the shale. In...
#1Yongting Duan(CAS: Chinese Academy of Sciences)H-Index: 3
#2Xiao Li(CAS: Chinese Academy of Sciences)H-Index: 15
Last. Runqing Zhou(CAS: Chinese Academy of Sciences)H-Index: 2
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In order to investigate the meso-damage evolution of shale, four uniaxial compressive tests were conducted using X-ray micro-computed tomography (micro-CT) equipment. Two of the four samples were conducted the in situ compression tests, from which a series of CT images at different stress levels were got during the loading process. Based on those CT images, a new damage variable was first proposed to quantitatively analyze the damage evolution of shale under uniaxial compression condition. Analy...
#1Yanlin Zhao(CUMT: China University of Mining and Technology)H-Index: 21
#2Yixian Wang(Hefei University of Technology)H-Index: 20
Last. Jin-Zhou Tang(Hunan University of Science and Technology)H-Index: 3
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Abstract This paper presents an extensive laboratory investigation of the non-linear rheological mechanical characteristics of hard rock under cyclic incremental loading and unloading. A data processing algorithm is proposed to analyze the experimental data, determine the instantaneous elastic and plastic strain components, visco-elastic and visco-plastic strain components from the total strain, and separate the visco-elastic and visco-plastic strain curves from the total creep strain curves. Th...
#1Heng Zhao(CSU: Central South University)H-Index: 11
#1Heng Zhao(CSU: Central South University)H-Index: 1
Last. Xibing Li(CSU: Central South University)H-Index: 44
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AbstractStatistical damage constitutive models (SDCMs) have been widely employed to describe the mechanical response of strain-softening rock, especially in brittle failure under moderate confining pressure. The residual strength, referring to the strength of strain-softening rock in the postpeak region, has not been accurately considered in present works. In this study, an extended definition of damage was proposed based on the fact that the intact material gradually evolves into another damage...
#1Chao Liang(China University of Geosciences)H-Index: 14
#2Zaixing Jiang(China University of Geosciences)H-Index: 18
Last. Juan Li(China University of Geosciences)H-Index: 1
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Abstract The Lower Silurian Longmaxi Formation is a key target for shale-gas exploration in South China and comprises organic-rich black shale unit deposited in an anoxic deep-water setting. Mineral components are dominated by quartz and clay minerals with minor amounts of plagioclase, potassium feldspar, calcite and pyrite. The brittle mineral content ranges from 45% to 80% by weight (average: 62.5 wt. %). Organic geochemical analyses (TOC, organic matter type, Ro and gas content) show that the...
When rock samples are loaded until macroscopic fractures develop, the failure process can be divided into several stages based on axial and lateral strain responses or the acoustic emission sequence during uniaxial compression tests. Several stress thresholds may be identified: the crack closure stress σ cc, crack initiation stress σ ci, crack damage stress σ cd, and uniaxial compressive strength σ ucs; these may be used as a warning indicator for rock rupture. We investigated the crack damage s...
The increase amplitude of residual strength of rock is larger than the rock peak intensity of rock with the increase of confining pressure.Gradually,residual strength becomes the main factor of complete stress-strain curve of rock at the stage after peak intensity.While establishing statistical damage constitutive model,it’s necessary to modify the residual strength.Based on the strain strength theory and hypothesis of rock particles intensity obeying Weibull random distribution,a statistical da...
Based on a probabilistic model of brittle microfracture (microdamage) leading to macrofracture of materials, we propose a statistical interpretation of strength criteria, which relate start of macrofracture (manifested by macrocrack formation in tension or internal structure stability loss in compression) with attainment of a certain (critical) value of density of microdefects in the material under study. The criterion is reduced to comparative analysis of microdefect density induced by the part...
#1Xiao Wei Li(CUMT: China University of Mining and Technology)H-Index: 1
#2Cheng Lin Jiang(CUMT: China University of Mining and Technology)H-Index: 1
Last. Ming Ji(CUMT: China University of Mining and Technology)H-Index: 1
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the evolution of rock microdefect is a random variation, and we can consider evolutionary process of microdefect system as nonequilibrium statistic processes. The microbit’s intensity distribution obey Weibull distribution, therefore, this paper adopts Druckr-Prager yield criterion, establishes the damage evolution equation using strain as characteristic parameter under the uniaxial stress, and derives relevant damage constitutive equation. Experiments prove that this equation, to some extent, r...
#1Enyuan Wang(CUMT: China University of Mining and Technology)H-Index: 35
#2Xueqiu He(CUMT: China University of Mining and Technology)H-Index: 13
Last. Z. T. Liu(CUMT: China University of Mining and Technology)H-Index: 1
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Based on the coupling mechanism of stress and electricity of EME of coal or rock and the theory of statistic damage mechanics, the coupling model of stress and electricity of EME of coal or rock is established in this paper, which is modified by simulation study on Weibull morphological parameter m. Then this model becomes more accurate and useful. The value of m and EME of different coal or rock samples are simulated by using the modified coupling model of stress and electricity of EME of coal ...
Last. Haibo Li(CAS: Chinese Academy of Sciences)H-Index: 16
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Enhanced geothermal system technology is in the focus of geothermal energy research due to its large economic growth potential. This study illustrates a pseudo-3D doublet model of EGS using coupled thermo-hydro-mechanical-damage modeling processes in the framework of TOUGHREACT-FLAC3D. Three cases were simulated to evaluate the effect of anisotropic permeability (η=5, 1, 0.2) on conducting damage, inducing permeability evolution, reducing elastic module, changing reservoir pressure, and thermal ...
A correlation study between the fracability and brittleness of shale gas reservoir is crucial for optimize reservoir reconstruction and enhance shale gas recovery. To investigate the relationship between fracability and brittleness of shale, a series of uniaxial compression tests of Silurian Longmaxi shale samples were carried out using a novel setup that combines X-ray micro-computed tomography with a uniaxial loading apparatus. Based on the CT images obtained from the test, fractal dimension o...
#1Xin Huang(Anhui University of Science and Technology)H-Index: 1
#2Jianyong Pang(Anhui University of Science and Technology)H-Index: 3
Last. Yu Chen(Anhui University of Science and Technology)H-Index: 1
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Underground engineering, especially deep geotechnical engineering, is often affected alternately by groundwater infiltration and ventilation drying during construction and use. In addition, acid rain, mineral dissolution, acid deposition, and other factors make groundwater acidic. This caused the underground structure to erode and has also threatened its safety and durability. In this study, both the physical and mechanical properties under acid dry-wet (A-D-W) cycles were investigated. Deep san...
Abstract The article reports a study on the ‘goodness of fit’ of Weibull and Normal (Gaussian) distributions on the compressive strength and the corresponding Acoustic Emissions (AE) of cementitious materials. An attempt has been made to understand the variation of the parameters of the Weibull distribution and the Gaussian distribution carried out on the uniaxial compressive strength data and the corresponding recorded AE parameters. The statistical analysis of ‘Damage Parameter’ based on the p...