The meso-fracturing mechanism of marble under unloading confining pressure paths and constant axial stress

AbstractFailure tests on marble during unloading confining-pressure under constant axial stress and simulations with the particle flow code were performed. The influence mechanism of the unloading rate of the confining pressure, initial unloading stress, and confining pressure on the failure characteristics of, and crack propagation in, marble was studied. By using the trial-and-error method, the conversion relationship between the unloading rates of confining pressures in laboratory tests and numerical simulations was ascertained. Micro-cracks formed in the unloading process of confining pressure are dominated by tension cracks, accompanied by shear cracks. The propagation of shear cracks lags that of tension cracks. As the confining pressure is increased, more cracks occur upon failure of the samples. The proportion of shear cracks increases while that of tension cracks decreases. The failure mode of samples undergoes a transition from shear-dominated failure to conjugated shear failure.

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Research on Microscopic Evolution Laws of Sandstone Deformation and Failure Based on the Particle Discrete Element Method

Mathematical Problems in Engineering ◽

10.1155/2021/8282493 ◽

2021 ◽

Vol 2021 ◽

pp. 1-12

Author(s):

Zhiwei Cai ◽

Tongqing Wu ◽

Jian Lu ◽

Yue Wu ◽

Nianchun Xu

Keyword(s):

Shear Crack ◽

Rock Fracture ◽

Confining Pressure ◽

Particle Flow Code ◽

Shear Cracks ◽

Deformation And Failure ◽

Fracture Development ◽

Confining Pressures ◽

The Law ◽

Microcrack Growth

The fracture of sandstone is closely related to the condition of internal microcracks and the fabric of micrograin. The macroscopic mechanical property depends on its microscopic structures. However, it is difficult to obtain the law of the microcrack growth under loading by experiments. A series of microscopic sandstone models were established with particle flow code 3D (PFC3D) and based on the triaxial experiment results on sandstones. The experimental and numerical simulations of natural and saturated sandstones under different confining pressures were implemented. We analyzed the evolution of rock deformation and the rock fracture development from a microscopic view. Results show that although the sandstones are under different confining pressures, the law of microcrack growth is the same. That is, the number of the microcracks increases slowly in the initial stage and then increases exponentially. The number of shear cracks is more than the tensile cracks, and the proportion of the shear cracks increases with the increase of confining pressure. The cracking strength of natural and saturated sandstones is 26% and 27% of the peak strength, respectively. Under low confining pressure, the total number of cracks in the saturated sample is 20% more than that of the natural sample and the strongly scattered chain is barely seen. With the increase of the confining pressure, the effect of water on the total number of cracks is reduced and the distribution of the strong chain is even more uniform. In other words, it is the confining pressure that mainly affects the distribution of the force chain, irrespective of the state of the rock, natural or saturated. The research results reveal that the control mechanism of shear crack friction under the different stress states of a rock slope in the reservoir area provides a basis for evaluating the stability of rock mass and predicting the occurrence of geological disasters.

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Study on Strength Properties and Crack Expansion Evolution Laws of Rock Containing Multiple Fissures

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.353-356.608 ◽

2013 ◽

Vol 353-356 ◽

pp. 608-613 ◽

Cited By ~ 1

Author(s):

Hong Hui Zhao ◽

Hong Wen Jing ◽

Hai Jian Su

Keyword(s):

Failure Process ◽

Confining Pressure ◽

Strength Properties ◽

Test System ◽

Shear Cracks ◽

High Confining Pressure ◽

Confining Pressures ◽

Hydraulic Servo ◽

Evolution Laws ◽

Tension Cracks

Through experiments that were carried out to study the rock-like specimens with nine fissures under uniaxial compression by YNS2000 electro-hydraulic servo test system, to reveal the mechanism about strength and mechanism about crack expansion evolution laws of rock containing multiple fissures. Applying numerical simulation (RFPA) for the whole failure process of rock containing multiple fissures with reasonable parameters, the results present the influence mechanism of different confining pressures for strength and crack expansion characteristics. The experimental results show: the peak strength of specimens with nine fissures degrades obviously compared with complete specimens; Specimens containing multiple fissures begin to crack with tension cracks, and break with shear cracks finally. With the increase of confining pressure, the compressive strength of rock containing multiple fissures increases gradually; And crack expansion generally occurs on the middle diagonal fissure-plane under high confining pressure.

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Failure Characteristics and Mechanism of Multiface Slopes under Earthquake Load Based on PFC Method

Shock and Vibration ◽

10.1155/2021/9329734 ◽

2021 ◽

Vol 2021 ◽

pp. 1-11

Author(s):

Tao Yang ◽

Yunkang Rao ◽

Huailin Chen ◽

Bing Yang ◽

Jiangrong Hou ◽

...

Keyword(s):

Moisture Content ◽

Failure Mechanism ◽

Failure Modes ◽

Shear Failure ◽

Shaking Table ◽

Tensile Failure ◽

Particle Flow Code ◽

Shear Cracks ◽

Local Shear ◽

Shear Slip

Understanding the failure mechanism and failure modes of multiface slopes in the Wenchuan earthquake can provide a scientific guideline for the slope seismic design. In this paper, the two-dimensional particle flow code (PFC2D) and shaking table tests are used to study the failure mechanism of multiface slopes. The results show that the failure modes of slopes with different moisture content are different under seismic loads. The failure modes of slopes with the moisture content of 5%, 8%, and 12% are shattering-shallow slip, tension-shear slip, and shattering-collapse slip, respectively. The failure mechanism of slopes with different water content is different. In the initial stage of vibration, the slope with 5% moisture content produces tensile cracks on the upper surface of the slope; local shear slip occurs at the foot of the slope and develops rapidly; however, a tensile failure finally occurs. In the slope with 8% moisture content, local shear cracks first develop and then are connected into the slip plane, leading to the formation of the unstable slope. A fracture network first forms in the slope with 12% moisture content under the shear action; uneven dislocation then occurs in the slope during vibration; the whole instability failure finally occurs. In the case of low moisture content, the tensile crack plays a leading role in the failure of the slope. But the influence of shear failure becomes greater with the increase of the moisture content.

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Experimental Research on Deformation Characteristics and Energy Change of Rock under Different Unloading Rates of Confining Pressures

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.243-249.2885 ◽

2011 ◽

Vol 243-249 ◽

pp. 2885-2888

Author(s):

Xian Min Han ◽

Shou Ding Li

Keyword(s):

Rock Mass ◽

Energy Release ◽

Rock Burst ◽

Experimental Research ◽

Volumetric Strain ◽

Confining Pressure ◽

Deformation Characteristics ◽

Confining Pressures ◽

Unloading Rate ◽

Unloading Confining Pressure

Experiments of unloading confining pressure of rock were conducted to reveal deformation characteristics of rock mass under different excavation intension in thigh geostress condition. It were concluded from tests that volumetric strain of rock is inverse proportional to unloading rate. The smaller the unloading rate, the bigger the ductility of rock. Energy release are bigger under high unloading rate than that under low unloading rate. That means that tendency of rock burst turn smaller when unloading rates decrease.

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The Effect of Sampling on the Undrained Soil Properties of a Leda Soil

Canadian Geotechnical Journal ◽

10.1139/t71-056 ◽

1971 ◽

Vol 8 (4) ◽

pp. 546-557 ◽

Cited By ~ 9

Author(s):

Gerald P. Raymond ◽

David L. Townsend ◽

Miroslav J Lojkasek

Keyword(s):

Sampling Method ◽

Sampling Methods ◽

Axial Stress ◽

Pressure Coefficient ◽

Confining Pressure ◽

Stress Difference ◽

Consolidation Pressure ◽

Failure Index ◽

Confining Pressures ◽

Leda Clay

The comparison of consolidated undrained triaxial results on sensitive Leda clay sampled by six different sampling methods is presented. The results indicate that the failure index, represented by the axial stress difference as a fraction of the axial failure stress difference against strain plots, are widely different at very low consolidation pressures, but are similar and approximate to the results from block samples as the consolidation pressure is increased. The pore pressure coefficient A appears to be independent of the sampling method and remains remarkably consistent throughout any test (up to failure) except where the confining pressure is very low or above the preconsolidation pressure.Routine commercial sampling methods (including laboratory preparation) using 50-mm diameter samples were found to partially destroy the cementation bonds, causing a decrease in strength at low confining pressures and an unsafe increase in strength at medium confining pressures. This trend is decreased by better sampling.

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Study on stability of filling wall under lateral large-span composite hinge fracture of hard critical block

Science Progress ◽

10.1177/00368504211021694 ◽

2021 ◽

Vol 104 (2) ◽

pp. 003685042110216

Author(s):

Chenghai Li ◽

Yajie Liu ◽

Jianbiao Bai ◽

Qing Ge

Keyword(s):

Field Test ◽

Shear Failure ◽

Lateral Displacement ◽

Axial Stress ◽

Tensile Failure ◽

Shear Cracks ◽

Large Span ◽

The Stability ◽

Number Of Segments ◽

Hinge Fracture

There is still a lack of mature researches on the stability mechanism, influencing factors and control technology of the gob-side filling wall, and systematic researches on the cracking forms and characteristics of the stope roof and the stability of the filling wall are rather insufficient. This paper is aimed at investigating the deformation law of the filling wall under the large-span composite hinge fracture of the hard critical block and solving the difficulty that the large-span critical block lateral fracture poses to gob-side entry retaining. Research methods such as theoretical calculation, mechanical analysis, numerical simulation and field test were adopted comprehensively in this study. When the large-span critical block B is divided into two or three parts, its force on the immediate roof decreases with the increase in the number of segments. Meanwhile, as the number of segments grows, the displacement and axial stress of the filling wall both decrease gradually; the tensile failure weakens relatively, while the shear failure changes slightly. Moreover, both the number of shear cracks and the number of tensile cracks in the filling wall are positively correlated with the strain. When the critical block divided into four parts, the amount of lateral displacement is about 190 mm, and the axial displacement reaches the minimum (about 235 mm). The stability of the filling wall along the gob-side entry is closely related to the lateral fracture span of the stope roof. Under the lateral fracture of the hard critical block, a smaller span of the lateral fracture of the critical block corresponds to a smaller force on the filling wall and a weaker damage to the filling wall. The field test result verifies that cleaving the large-span critical block into smaller segments is conducive to reducing surrounding rock and filling wall deformation.

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Prefabricated Structures Surface Marble Rheological Tests and Constitutive Model Analysis

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.501-504.419 ◽

2014 ◽

Vol 501-504 ◽

pp. 419-425

Author(s):

Qing Xu ◽

Jiang Da He ◽

Hong Qiang Xie ◽

Ming Li Xiao ◽

Jian Feng Liu

Keyword(s):

Mechanical Properties ◽

Rheological Properties ◽

Flow Rate ◽

Axial Stress ◽

Triaxial Compression ◽

Confining Pressure ◽

Rheological Parameters ◽

Structural Plane ◽

High Confining Pressure ◽

Confining Pressures

The mechanical properties of intact rock and rock containing structural plane are very different. From the diversion tunnel of Jinping deep rock site to retrieve the complete block of marble, after a high confining pressure triaxial compression simulation tectonic movements, the formation of structural plane, it represents the mechanical properties of the original rock. On the surface of the marble structure containing triaxial compression creep tests, the results showed: at low confining pressure, the weak marble surface as micro-damage accumulation, the emergence of non-uniform partial destruction, while at high confining pressure, creep curve better continuity and integrity; different confining pressures, marble initial rheology and stability both appear rheological phase, accelerated phase rheological obvious; different confining pressures, the same stage of the axial stress steady flow rate compared with the confining pressure increases, the axial steady state flow rate becomes smaller; marble under test showed the rheological properties, the use of Nishihara model can better demonstrate the rheological properties and determine the rheological parameters for other practical engineering reference.

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Experimental study on permeability characteristics of gas-containing raw coal under different stress conditions

Royal Society Open Science ◽

10.1098/rsos.180558 ◽

2018 ◽

Vol 5 (7) ◽

pp. 180558 ◽

Cited By ~ 8

Author(s):

Dongming Zhang ◽

Yushun Yang ◽

Hao Wang ◽

Xin Bai ◽

Chen Ye ◽

...

Keyword(s):

Flow Rate ◽

Coal Sample ◽

Axial Stress ◽

Axial Strain ◽

Confining Pressure ◽

Gas Pressure ◽

Permeability Characteristics ◽

Loading And Unloading ◽

Unloading Confining Pressure ◽

Function Relation

The present experimental study on permeability characteristics for raw coal under different stress states is implemented by applying the triaxial self-made ‘THM coupled with servo-controlled seepage apparatus for gas-containing coal’; the result indicates that the flow rate of gas in the coal sample gradually decreases with the nonlinear loading of axial pressure and increases with the nonlinear unloading of axial stress and confining pressure. The flow rate, axial stress and confining pressure curves all satisfy the negative exponential function relation. When the sample reaches the peak intensity, the sample will be destroyed and the stress will drop rapidly; then the flow rate of the sample will increase rapidly. At this stage, the flow rate and axial strain show an oblique ‘v' pattern. The flow rate of the coal sample increases nonlinearly with the increase of gas pressure; the relation curve between flow rate and gas pressure satisfies the power function relation. Under the same confining pressure and gas pressure conditions, the larger the axial stress, the smaller the flow rate of the coal sample. Under the same axial stress and gas pressure conditions, the flow rate of the coal sample will first decrease, but then increase as the confining pressure decreases. During the post-peak loading and unloading process, the flow rate of the coal sample will decrease with the loading of confining pressure but increase with the unloading of confining pressure, and there will be an increase in wave shape with the increase in axial strain. The flow rate of each loading and unloading confining pressure is higher than that of the previous loading and unloading confining pressure. At the post-peak stage, the relation curve between the flow rate of the coal sample and the confining pressure satisfies the power function relation in the process of loading and unloading confining pressure.

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Long-term creep behavior of deep-buried marble under different confining pressures

Thermal Science ◽

10.2298/tsci180615078z ◽

2019 ◽

Vol 23 (Suppl. 3) ◽

pp. 653-660

Author(s):

Ersheng Zha ◽

Ru Zhang ◽

Zetian Zhang ◽

Li Ren ◽

Wenju Zhang ◽

...

Keyword(s):

Creep Behavior ◽

Shear Failure ◽

Confining Pressure ◽

Tensile Failure ◽

Creep Failure ◽

Failure Characteristics ◽

Underground Caverns ◽

Confining Pressures ◽

Term Creep

To explore the long-term creep behavior of deep rock, the long-term tri-axial creep mechanical behavior of the rock under different confining pressures has been carried out. The results show that the instantaneous strain and creep strain of the high confining pressure specimen are significantly higher than that of the low confining pressure specimen under high deviatoric stress. By analyzing the failure characteristics of different confining pressure specimens, it is found that with the increase of the confining pressure, the creep failure characteristics of the marble transforms from tensile failure to shear failure. These research results have certain reference significance for the long-term stability analysis of the deep underground caverns.

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Investigation on the Influence of Temperature and Confining Pressure on the Hydraulic Conductivity of the Integrated and Fractured Jurassic Conglomerates

Geofluids ◽

10.1155/2021/8858030 ◽

2021 ◽

Vol 2021 ◽

pp. 1-13

Author(s):

Dingyang Zhang ◽

Wanghua Sui ◽

Jiawei Liu

Keyword(s):

Hydraulic Conductivity ◽

Shear Failure ◽

Negative Relationship ◽

Confining Pressure ◽

Regression Equations ◽

Intact Sample ◽

Triaxial Cell ◽

Different Temperatures ◽

Confining Pressures ◽

Constant Head

This paper presents an experimental investigation on the properties of hydraulic conductivity and permeability of conglomerates under different temperatures and confining pressures with integrated samples and samples with shear failure. Constant head tests were carried out in a temperature-controlled triaxial cell with samples obtained from the Zhuxianzhuang Coal Mine. Five levels of temperatures (10°C, 20°C, 28°C, 35°C, and 50°C) and three levels of confining pressures (3 MPa, 5 MPa, and 7 MPa) were chosen for the tests. The results show that there is a negative relationship between hydraulic conductivity and confining pressure with both original and shear failure samples. An inflection point of 35°C is found in the relationship between the flow rate and temperature. However, with increasing temperature conditions, hydraulic conductivity first increases and then decreases at 50°C with the intact sample, while hydraulic conductivity first decreases from 20°C and then increases with the shear failure sample. Finally, nonlinear regression equations of hydraulic conductivity and temperature were obtained under different confining pressures.

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