Particle Flow Analysis of Mechanical Properties and Failure Behaviour in Composite Rock Strata with Holes

Understanding the deformation failure behavior of the composite rock strata has important implications for deep underground engineering construction. Based on the uniaxial compression laboratory test of the specimens of composite rock strata containing holes, the microscopic parameters in the particle discrete element simulation are firstly calibrated. Then, the mechanical properties and failure characteristics of the composite rock strata with holes under different confining pressures are studied. The results show that different dip angles and confining pressures have significant effects on the peak strength and elastic modulus of the specimens. Under the same confining pressure, the peak strength and elastic modulus decrease first and then increase with the increasing dip angle. As the dip angle is constant, both the peak strength and elastic modulus gradually increase with the increase in confining pressure. It shows that the first area to be damaged in composite rock strata transfers from soft rock to hard rock with the increase in dip angle. With the increase in confining pressure, the range of tensile stress concentration area decreases substantially, while the range of compressive stress concentration area changes less.

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Experimental Study on the Anisotropy of Layered Rock Mass under Triaxial Conditions

Advances in Civil Engineering ◽

10.1155/2021/2710244 ◽

2021 ◽

Vol 2021 ◽

pp. 1-13

Author(s):

Long Cheng ◽

Hui Wang ◽

Xu Chang ◽

Yewei Chen ◽

Feilu Xu ◽

...

Keyword(s):

Mechanical Properties ◽

Confining Pressure ◽

Peak Strength ◽

Rock Composition ◽

Rock Formations ◽

Geological Conditions ◽

Anisotropic Mechanical Properties ◽

Confining Pressures ◽

Dip Angle ◽

Rock Specimens

Weak and hard inhomogeneous rock formations are typically encountered during tunnel excavations. The physical and mechanical properties and geological conditions of these rock formations vary significantly; thus, it is crucial to investigate the mechanical characteristics of deep bedded composite rock formations. Three-dimensional (3D) scanning and 3D printing were used to prepare composite rock specimens to simulate natural rock laminae. Triaxial compression tests were conducted to determine the influence of the bedding angle, rock composition, and confining pressure on the mechanical properties of the composite rock specimens. The anisotropic strength characteristics and the damage patterns of the composite rock specimens were analyzed under different confining pressures, and the failure mechanism during triaxial loading was revealed. The results show that the damage of the composite rock specimens with a bedding structure depends on the bedding dip angle and the rock formation. The stress-strain curves and peak strengths of the composite rock specimens have anisotropic characteristics corresponding to their failure modes. As the bedding dip angle increases, the peak strength of the three groups of specimens first decreases and then increases under different confining pressure levels. The compressive strength has a nonlinear relationship with the confining pressure, and the difference between the compressive strengths of specimens with different inclination angles decreases as the confining pressure increases. The Hoek–Brown strength criterion is a good predictor of the nonlinear increase in peak strength of the composite rock specimens under different confining pressures. The specimen with a β = 60°dip angle shows the most significant increase in the strength difference with increasing confining pressure. The results can be used as a reference for testing and analyzing the anisotropic mechanical properties of bedded rock masses.

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MECHANICAL PROPERTIES OF SANDSTONE SUBJECTED TO COUPLING OF TEMPERATURE–SEEPAGE–STRESS

DYNA INGENIERIA E INDUSTRIA ◽

10.6036/10055 ◽

2021 ◽

Vol 96 (3) ◽

pp. 309-315

Author(s):

Lijie Long ◽

Dongyan Liu ◽

Dong Wang ◽

Jin Li

Keyword(s):

Mechanical Properties ◽

Plastic Deformation ◽

Rock Mass ◽

Elastic Modulus ◽

Plastic Zone ◽

Residual Strength ◽

Confining Pressure ◽

Peak Strength ◽

Hydraulic Pressure ◽

Stress Strain

ABSTRACT: The deformation and fracture of rock mass in deep rock mass engineering are affected by the coupling of temperature, seepage, and stress. A test and a calculation model for sandstone under thermal–hydrological–mechanical (THM) coupling were proposed to reveal the mechanical properties of sandstone. The law of coupling for mechanical indicators of sandstone was established by laboratory tests and numerical simulations. The permeability, peak strength, peak strain, residual strength, elastic modulus, plastic deformation area, and stress–strain cloud diagram were analyzed by the steady state seepage method and THM coupling principle, and the accuracy of the model was verified. Results demonstrate that: (1) As the temperature rises and the peak deformation increases, the sample slowly drops to the residual strength level after the peak stress. (2) The main factor that affects peak strength is confining pressure. In the temperature range of 25 °C–50 °C, the maximum peak strength and peak deformation are increased by heating, and the increases in confining pressure and temperature reduce the reduction coefficient of the residual strength. Moreover, the elastic modulus increases with the increase in confining pressure, but it shows a downward trend when the temperature increases. (3) The plastic deformation zone and stress–strain cloud diagram indicated that when the temperature and osmotic pressure increase, the specimen enters the plastic zone earlier, the effective plastic zone increases, the stress increases, and the deformation is intensified. The proposed method provides a certain reference for the permeability and stability evaluation of rock mass under the conditions of “three-high” (high confining pressure, high hydraulic pressure, and high stress) engineering. Keywords: temperature–seepage–stress coupling, sandstone, mechanical properties

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The Conventional Triaxial Compressive Test of Plain Reactive Powder Concrete

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.670-671.401 ◽

2014 ◽

Vol 670-671 ◽

pp. 401-406

Author(s):

Xiao Fei Wang ◽

Yang Ping Wang

Keyword(s):

Elastic Modulus ◽

Failure Modes ◽

Shear Failure ◽

Poisson Ratio ◽

Confining Pressure ◽

Peak Strength ◽

Reactive Powder Concrete ◽

Peak Strain ◽

Confining Pressures ◽

Reactive Powder

Through the conventional triaxial test about plain reactive powder concrete under different confining pressures at 0Mpa, 25 Mpa,50 Mpa and 75 Mpa, this paper obtained the stress-strain curves in axial direction and radial direction of plain reactive powder concrete under different confining pressures, compared and analyzed the effects of confining pressures on peak strength, peak strain, Elastic modulus, Poisson ratio and failure modes of plain reactive power concrete also. The results showed that peak strength increases with the increase of confining pressure, when confining pressure increases from 0Mpa to 25Mpa, the peak strength increases most rapidly. The results also showed that peak strain increases linearly with the increase of confining pressure, when confining pressure increase from 0Mpa to 75Mpa gradually, the peak strain increases from 0.2 percent to 0.93 percent, meanwhile Poisson ratio increase with the increase of confining pressures, yet Elastic modulus changes slight at different confining pressures, failure modes of plain reactive powder concrete at different confining pressures exhibit different modes, when confining pressure is 0Mpa, failure mode presents as splitting failure, shear failure mode at 25Mpa, while shear failure merge local crushing at 50MPa and 75MPa.

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Physical and Mechanical Properties of a Bulk Lightweight Concrete with Expanded Polystyrene (EPS) Beads and Soft Marine Clay

Materials ◽

10.3390/ma12101662 ◽

2019 ◽

Vol 12 (10) ◽

pp. 1662 ◽

Cited By ~ 4

Author(s):

Jianguo Wang ◽

Bowen Hu ◽

Jia Hwei Soon

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Cement Content ◽

Mass Density ◽

Physical And Mechanical Properties ◽

Confining Pressure ◽

Expanded Polystyrene ◽

Triaxial Tests ◽

Filling Material ◽

Confining Pressures

The variation of physical and mechanical properties of the lightweight bulk filling material with cement and expanded polystyrene (EPS) beads contents under different confining pressures is important to construction and geotechnical applications. In this study, a lightweight bulk filling material was firstly fabricated with Singapore marine clay, ordinary Portland cement and EPS. Then, the influences of EPS beads content, cement content, curing time and confining pressure on the mass density, stress–strain behavior and compressive strength of this lightweight bulk filling material were investigated by unconsolidated and undrained (UU) triaxial tests. In these tests, the mass ratios of EPS beads to dry clay (E/S) were 0%, 0.5%, 1%, 2%, and 4% and the mass ratios of cement to dry clay (C/S) were 10% and 15%. Thirdly, a series of UU triaxial tests were performed at a confining pressure of 0 kPa, 50 kPa, 100 kPa, and 150 kPa after three curing days, seven curing days, and 28 curing days. The results show that the mass density of this lightweight bulk filling material was mainly controlled by the E/S ratio. Its mass density decreased by 55.6% for the C/S ratio 10% and 54.9% for the C/S ratio 15% when the E/S ratio increased from 0% to 4% after three curing days. Shear failure more easily occurred in the specimens with higher cement content and lower confining pressure. The relationships between compressive strength and mass density or failure strain could be quantified by the power function. Increasing cement content and reducing EPS beads content will increase mass density and compressive strength of this lightweight bulk filling material. The compressive strength with curing time can be expressed by a logarithmic function with fitting correlation coefficient ranging from 0.83 to 0.97 for five confining pressures. These empirical formulae will be useful for the estimation of physical and mechanical properties of lightweight concretes in engineering application.

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Study on Damage Model and Damage Evolution Characteristics of Backfill with Prefabricated Fracture under Seepage-Stress Coupling

Advances in Materials Science and Engineering ◽

10.1155/2020/3642356 ◽

2020 ◽

Vol 2020 ◽

pp. 1-11

Author(s):

Jifeng Hou ◽

Zhongping Guo ◽

Weizhen Liu ◽

Hengze Yang ◽

WenWu Xie

Keyword(s):

Mechanical Properties ◽

Damage Evolution ◽

Coupling Effect ◽

Water Pressure ◽

Damage Model ◽

Confining Pressure ◽

Seepage Water ◽

Confining Pressures ◽

Initial Fracture ◽

Total Damage

Aiming at the backfill with prefabricated fracture under seepage-stress coupling, the concepts of fracture macrodamage, loaded mesodamage, seepage mesodamage, and total damage of backfill were proposed. Based on the macroscopic statistical damage model, the coupling effect of seepage, stress, and initial fracture was considered comprehensively and the damage model of backfill with prefabricated fracture under seepage-stress coupling was established. The mechanical properties of backfill with prefabricated fracture under different seepage water pressures and confining pressures were tested and the rationality of the model was verified. The research shows that the mechanical properties of backfill with prefabricated fracture under the seepage-stress coupling are determined by the seepage water pressure, the load, the initial fracture, and the coupling effect. Fracture and seepage have significant effects on the damage of the backfill. When the seepage water pressure is low, the fracture damage dominates; however, when the seepage water pressure is high, the seepage damage dominates; the total damage under the coupling action is more serious than the single factor. The development laws of the total damage evolution curves under different seepage water pressures and confining pressures are basically the same, and they show the S-shaped distribution law with the increase of the axial strain. With the increase of confining pressure, the damage effect of fracture and seepage on the backfill is weakened, indicating that the confining pressure has a certain inhibitory effect on the damage evolution of the backfill. The research results can provide a theoretical basis for the study of the stability of backfill with geological defects such as joints and fractures in deep high-stress and high-seepage water pressure coal mines.

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Experimental and Numerical Investigation of Failure Characteristics and Mechanism of Granites with Different Joint Angles

Shock and Vibration ◽

10.1155/2021/6890833 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Zhenhua Wang ◽

Jun Fang ◽

Gang Wang ◽

Yifan Jiang ◽

Dongwei Li

Keyword(s):

Elastic Modulus ◽

Uniaxial Compression ◽

Elastic Strain Energy ◽

Peak Stress ◽

Peak Strength ◽

Particle Flow Code ◽

Dissipated Energy ◽

Shear Cracks ◽

Compression Tests ◽

Dip Angle

The uniaxial compression tests were conducted on granite samples with different joint dip angles to more favorably explore the influences of the nonconsecutive joint on mechanical properties and deformation characteristics of the rock mass. The stress-strain curves, deformation and strength characteristics, and energy evolution process of the samples were analyzed. Numerical simulation using particle flow code (PFC) is employed to study the crack propagation process. The mode of jointed and fractured rock was investigated. The research results showed a significant reduction in both the peak strength and elastic modulus of jointed samples compared with intact ones: the peak strength and elastic modulus drop to the minimum at the joint dip angle of about 45°, especially for the peak strength, which takes up about 55% of the intact samples. The fractured samples’ total energy, elastic strain energy, and dissipated energy during the uniaxial compression drop significantly relative to intact samples. The proportion of the fracture modes varies with different joint dip angles, in which the ratio of shear cracks grows at first and then declines, with the highest balance at the dip angle of 45°. The damage stress’s sensitivity to the dip angle change is greater than that of the peak stress, with reduction amplitude more extensive than the latter.

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Study on Mechanical Failure and PermeabilityCharacteristicsof Porous Gas-Bearing Coal under Triaxial Stress

Shock and Vibration ◽

10.1155/2020/8838966 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10

Author(s):

Xue-bo Zhang ◽

Wen-yuan Wang ◽

Ming Yang ◽

Hang-hang Cai ◽

Jia-jia Liu ◽

...

Keyword(s):

Acoustic Emission ◽

Elastic Modulus ◽

Coal Sample ◽

Confining Pressure ◽

Gas Pressure ◽

Peak Strength ◽

Triaxial Stress ◽

Peak Strain ◽

Permeability Characteristics ◽

Gas Bearing

To explore the mechanical failure and permeability characteristics of porous gas-bearing coal under triaxial stress, the triaxial compression experiment was carried out for porous and conventional gas-bearing coal samples based on the triaxial creep-seepage experiment system and sound emission signal acquisition system. Acoustic emission testing was carried out at the same time of loading failure. The experimental results showed that (1) under fixed gas pressure but changing confining pressure, the porous gas-bearing coal sample had higher peak strength and elastic modulus but lower peak strain; under changing gas pressure but fixed confining pressure, the porous gas-bearing coal sample had lower peak strength and peak strain but higher elastic modulus. When either confining pressure or gas pressure was changed, the mechanical properties of the two kinds of gas-bearing coal samples showed a good consistency, but the mechanical parameters differed greatly, with the peak strength, peak strain, and elastic modulus of porous coal samples are reduced by 1/4, 2/3, and 3/4, respectively. (2) When either the confining pressure or gas pressure was changed, the permeability of the porous gas-bearing coal sample was larger than that of the conventional gas-bearing coal sample. However, the change rules of permeability characteristics of the two were basically the same, except that there was a large difference in permeability value that the porous gas-bearing coal sample increases nearly twice as much as that of the conventional gas-bearing coal sample. (3) In the whole stress-strain process, the acoustic emission characteristics of the porous gas-bearing coal sample differed significantly from those of the conventional gas-bearing coal sample. The maximum ringdown count of the porous gas-bearing coal sample can be reduced by one-third at most, the maximum energy can be reduced by nearly half at most, and the maximum amplitude changes little with only 1–3 dB reduction. The research results have important guiding significance for the prediction of failure and instability of coal tunnel and the development of relevant protective techniques.

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Experimental Investigation on the Influence of Water Content on the Mechanical Properties of Coal under Conventional Triaxial Compression

Shock and Vibration ◽

10.1155/2020/8872438 ◽

2020 ◽

Vol 2020 ◽

pp. 1-11

Author(s):

Meichang Zhang ◽

Rongshan Nie

Keyword(s):

Mechanical Properties ◽

Elastic Modulus ◽

Internal Friction ◽

Water Content ◽

Triaxial Compression ◽

Friction Angle ◽

Conventional Triaxial Compression ◽

Influence Of Water ◽

Confining Pressures ◽

Water Contents

The presence of water is one of the most important factors in coal mining, and it has a dual influence on the mechanical behavior of rock. To study the influence of water content on the mechanical properties of coal under complicated stress conditions, dry coal specimens and wet coal specimens with water contents of 1.8% and 3.6% were conducted by uniaxial and conventional triaxial compression tests. The relations between the uniaxial compressive strength, deformation, and water content were observed. The reductions in the strength and elastic modulus under different confining pressures were obtained. The mechanical properties of coal specimens with different water contents under triaxial compression were studied. The influences of water content on the microstructure, clay minerals, internal friction angle, and cohesive force of coal were discussed. The results show that the strengths and elastic moduli of wet specimens are clearly lower than those of dry specimens under different confining pressures. The water content has a significant influence on the postfailure mechanical behavior of coal. The loss rates of strength and elastic modulus decrease with increasing confining pressure. The water content has almost no effect on the internal friction angle, while the cohesive force of the saturated specimens is 36.5% lower than that of the dry specimens. The results can provide a reference for inhibiting the occurrence of disasters during coal mining and exploiting coal efficiently.

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SHPB Testing and Analysis of Bedded Shale under Active Confining Pressure

Journal of Engineering ◽

10.1155/2020/5034902 ◽

2020 ◽

Vol 2020 ◽

pp. 1-8

Author(s):

Guoliang Yang ◽

Jingjiu Bi ◽

Xuguang Li ◽

Jie Liu ◽

Yanjie Feng

Keyword(s):

Mechanical Properties ◽

Elastic Modulus ◽

Strain Rate ◽

Peak Stress ◽

Confining Pressure ◽

Dynamic Mechanical Properties ◽

Dynamic Elastic Modulus ◽

Peak Strain ◽

Dynamic Mechanical ◽

Bedding Angle

Shale gas is the most important new energy source in the field of energy, and its exploitation is very important. The research on the dynamic mechanical properties of shale is the premise of exploitation. To study the dynamic mechanical properties of shale from the Changning-Weiyuan area of Sichuan Province, China, under confining pressure, we used a split Hopkinson pressure bar (SHPB) test system with an active containment device to carry out dynamic compression tests on shale with different bedding angles. (1) With active confining pressure, the shale experiences a high strain rate, and its stress-strain curve exhibits obvious plastic deformation. (2) For the same impact pressure, the peak stress of shale describes a U-shaped curve with an increasing bedding angle; besides, the peak stress of shale with different bedding angles increases linearly with rising confining pressure. The strain rate shows a significant confining pressure enhancement effect. With active confining pressure, the peak strain gradually decreases as the bedding angle increases. (3) As a result of the influence of different bedding angles, the dynamic elastic modulus of shale has obvious anisotropic characteristics. Shale with different bedding angles exhibits different rates of increase in the dynamic elastic modulus with rising confining pressure, which may be related to differences in the development of planes of weakness in the shale. The results of this study improve our understanding of the behavior of bedded shale under stress.

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IMPACT OF WATER AND CO2 ON THE MECHANICAL PROPERTIES OF LOW PERMEABLE ROCKS

Tyumen State University Herald Physical and Mathematical Modeling Oil Gas Energy ◽

10.21684/2411-7978-2021-7-2-130-146 ◽

2021 ◽

Vol 7 (2) ◽

pp. 130-146

Author(s):

Anatolii A. KISLITSYN ◽

Nikita V. Lipatov

Keyword(s):

Mechanical Properties ◽

Triaxial Compression ◽

Confining Pressure ◽

Strength Properties ◽

Pore Fluid ◽

Co2 Injection ◽

Core Samples ◽

Different Temperatures ◽

Confining Pressures ◽

Temporary Decrease

This article features experiments on triaxial compression of low-permeable dolomite samples with different confining pressures (2-20 MPa), different pore fluids (dry air, water, CO2), and different temperatures (25-150 °C). The authors have studied the effect of confining pressure, pore fluid and temperature on the strength properties of the studied samples. The results show an increase in the strength with grwoing confining pressure. When the confining pressure increases from 2 to 20 MPa, the compressive strength increases from 86 to 370 MPa. Temperature has a significant effect on rock strength under low confining pressure conditions. With the increasing confining pressure reaching 15 MPa, increasing temperature has little effect on the strength of dolomite samples. Under an effective confining pressure of 5 MPa, the temperature weakening occurs on the dolomite specimens when the temperature exceeds 90 °C. During compression, liquid diffusion occurs in the specimens. Higher water viscosity can cause a temporary decrease in effective confining pressure, which can increase the strength of the rock. More prominent fractures are observed in the samples, and more fluid is injected under CO2 injection conditions, which may be useful for increasing the permeability of the geothermal reservoir. Two groups of experiments have been performed on the samples in this study: the first group of experiments investigated the effect of confining pressure on the fracture stress of core samples, without pore fluid injection; the second group of experiments investigated the effect of water or CO2 and temperature on the mechanical properties of core samples.

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