Experimental Investigations on Rheological Properties of Mudstone in Kilometer-Deep Mine

The soft rock roadway in deep high-stress environment has the problems of strong rheology and large deformation. Based on the analysis of the stress distribution of the surrounding rock of the roadway in a kilometer-deep mine, rheological tests under different stress paths are carried out for mudstone in a kilometer-deep mine. The rheological deformation curve, damage characteristics, and change rule of the main mechanical parameters of mudstone under different stress conditions are studied. The results show the following: (1) the peak strength of the triaxial compression of mudstone is closely related to confining pressure, and, with increasing confining pressure, the confining pressure effect decreases gradually; (2) the strain increases slowly under uniaxial loading, and, with increasing axial pressure, the velocity of rheological deformation increases nonlinearly, and the amount of mudstone deformation increases with time; (3) under the condition of unloading confining pressure with constant axial pressure, with decreasing confining pressure, the instantaneous axial and radial strains of mudstone specimen increase nonlinearly, the rheological strain and velocity of mudstone increase gradually, and the lateral rheological strain is close to the axial rheological strain; and, (4) in the unloading confining pressure with axial compression triaxial test, with increasing deviating stress, the axial and radial instantaneous strain increments of mudstone decrease gradually, the lateral strain and rheological velocity of mudstone increase gradually, and the lateral strain is approximately 2.05 times the axial strain. These conclusions reveal the rheological characteristics of the mudstone under different surrounding rock conditions and provide a theoretical basis for the excavation deformation and support control of roadways.

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Experimental Investigation of Energy Evolution in Sandstone Failure during Triaxial Unloading Confining Pressure Tests

Advances in Civil Engineering ◽

10.1155/2019/7419752 ◽

2019 ◽

Vol 2019 ◽

pp. 1-11 ◽

Cited By ~ 3

Author(s):

Rui Yang ◽

Depeng Ma ◽

Yongjie Yang

Keyword(s):

Elastic Energy ◽

Triaxial Compression ◽

High Stress ◽

Confining Pressure ◽

Energy Evolution ◽

Compression Tests ◽

Sandstone Sample ◽

Pressure Tests ◽

Unloading Confining Pressure ◽

Sample Damage

The deformation and failure of sandstone samples are closely related to energy changes in the material. To explore the energy evolution during the process of sandstone sample damage, loading and unloading tests with different test paths were conducted. The results show that more energy is stored and consumed before the stress reaches its peak, while after the peak stress, more energy is released and consumed. Energy dissipation increases internal cracking, leads to sample damage and lithologic deterioration, and reduces the bearing capacity of the sample. During triaxial unloading of the confining pressure, the higher the initial unloading confining pressure, the more the elastic energy stored, and the more the energy released when the sandstone sample fails, resulting in more severe damage. Therefore, during the excavation of high-stress rock masses, large amounts of elastic energy stored in sandstone can be rapidly released, leading to rock burst disasters. Additionally, during triaxial unloading confining pressure tests, the damage in sandstone when the sample is close to failure increases more rapidly than that during conventional triaxial compression tests because of the unloading effect of the confining pressure. This phenomenon also illustrates that the failure of sandstone induced by unloading is more sudden than that induced by loading.

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Experimental Investigation on the Deformation, Strength, and Acoustic Emission Characteristics of Sandstone under True Triaxial Compression

Advances in Materials Science and Engineering ◽

10.1155/2018/5241386 ◽

2018 ◽

Vol 2018 ◽

pp. 1-16 ◽

Cited By ~ 2

Author(s):

Zhaolin Li ◽

Lianguo Wang ◽

Yinlong Lu ◽

Wenshuai Li ◽

Kai Wang

Keyword(s):

Acoustic Emission ◽

Axial Strain ◽

Triaxial Compression ◽

Confining Pressure ◽

Lateral Strain ◽

Compression Tests ◽

True Triaxial ◽

Shear Slip ◽

True Triaxial Compression ◽

Triaxial Compression Tests

The study of deformation, strength, and other mechanical characteristics of sandstone under true triaxial compression is significant for understanding failure mechanisms in rock and evaluating the stability of underground structures. Conventional and true triaxial compression tests for sandstone are conducted for different stress states in this study using the self-developed true triaxial electrohydraulic servo test system combined with acoustic emission (AE) testing. This study presents an in-depth and systematic investigation of deformation, strength, and AE characteristics. The results show significant differences in deformation, strength, and acoustic emission characteristics for the rock under conventional triaxial and true triaxial compression tests, respectively. The peak strength, axial strain, lateral strain, and incremental strain (in unstable crack growth stage) increase with increasing confining pressure under conventional triaxial compression, and the AE count gradually decreases while shear crack proportion gradually increases, indicating that increasing confining pressure gradually inhibits the shear slip effect along fractures, delays perforation of the rock shear fracture surface, and enhances the ability of the rock to withstand deformation and load. Under true triaxial compression, the peak strength increases and then decreases with increasing intermediate principal stress σ2 and the axial strain ε1 and lateral strain ε2 gradually decrease; besides, the lateral strain (expansion) of the rock is mainly in the minimum principal stress σ3 direction, and lateral expansion tends to decrease before increasing. AE events first weaken and then enhance with increasing σ2, and the proportion of shear cracks increases first and then decreases, indicating that the confining pressure gradually changes from the shear slip effect that controls crack offset to the damage effect that promotes crack tension with increasing σ2. In addition, the protective effect of confining pressure improves when σ3 increases.

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Researches on the Constitutive Models of Artificial Frozen Silt in Underground Engineering

Advances in Materials Science and Engineering ◽

10.1155/2014/902164 ◽

2014 ◽

Vol 2014 ◽

pp. 1-8 ◽

Cited By ~ 4

Author(s):

Yugui Yang ◽

Feng Gao ◽

Hongmei Cheng ◽

Yuanming Lai ◽

Xiangxiang Zhang

Keyword(s):

Mechanical Characteristic ◽

Stress Level ◽

Strain Softening ◽

Triaxial Compression ◽

High Stress ◽

Constitutive Models ◽

Confining Pressure ◽

Frozen Soil ◽

Conventional Triaxial Compression ◽

Shear Process

The researches on the mechanical characteristic and constitutive models of frozen soil have important meanings in structural design of deep frozen soil wall. In the present study, the triaxial compression and creep tests have been carried out, and the mechanical characteristic of frozen silt is obtained. The experiment results show that the deformation characteristic of frozen silt is related to confining pressure under conventional triaxial compression condition. The frozen silt presents strain softening in shear process; with increase of confining pressure, the strain softening characteristic gradually decreases. The creep curves of frozen silt present the decaying and the stable creep stages under low stress level; however, under high stress level, once the strain increases to a critical value, the creep strain velocity gradually increases and the specimen quickly happens to destroy. To reproduce the deformation behavior, the disturbed state elastoplastic and new creep constitutive models of frozen silt are developed. The comparisons between experimental results and calculated results from constitutive models show that the proposed constitutive models could describe the conventional triaxial compression and creep deformation behaviors of frozen silt.

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Experimental Test on Nonuniform Deformation in the Tilted Strata of a Deep Coal Mine

Sustainability ◽

10.3390/su132313280 ◽

2021 ◽

Vol 13 (23) ◽

pp. 13280

Author(s):

Hai Wu ◽

Qian Jia ◽

Weijun Wang ◽

Nong Zhong ◽

Yiming Zhao

Keyword(s):

High Stress ◽

Stability Control ◽

Surrounding Rock ◽

Experimental Results ◽

Lower Side ◽

Reinforcement Scheme ◽

Deformation And Failure ◽

True Triaxial ◽

Deep Mine ◽

Deep Coal Mine

Taking a deep-mine horizontal roadway in inclined strata as our research object, the true triaxial simulation technique was used to establish a model of the inclined strata and carry out high-stress triaxial loading experiments. The experimental results show that the deformation of surrounding rock in the roadway presents heterogeneous deformation characteristics in time and space: the deformation of the surrounding rock at different positions of the roadway occurs at different times. In the process of deformation of the surrounding rock, deformation and failure occur at the floor of the roadway first, followed by the lower shoulder-angle of the roadway, and finally the rest of the roadway. The deformation amount in the various areas is different. The floor heave deformation of the roadway floor is the greatest and shows obvious left-right asymmetry. The deformation of the higher side is greater than that of the lower side. The model disassembly shows that the development of cracks in the surrounding rock is characterized by more cracks on the higher side and fewer cracks on the lower side but shows larger cracks across the width. The experimental results of high-stress deformation of the surrounding rock are helpful in the design of supports, the reinforcement scheme, and the parameter optimization of roadways in high-stress-inclined rock, and to improve the stability control of deep high-stress roadways.

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Comparison of Stress-Strain Relationships of FRP and Actively Confined High-Strength Concrete: Experimental Observations

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.919-921.29 ◽

2014 ◽

Vol 919-921 ◽

pp. 29-34 ◽

Cited By ~ 1

Author(s):

Jian Chin Lim ◽

Togay Ozbakkloglu

Keyword(s):

High Strength Concrete ◽

Axial Stress ◽

Axial Strain ◽

High Strength ◽

Confining Pressure ◽

Confined Concrete ◽

Lateral Strain ◽

Stress Strain ◽

Strength Concrete ◽

Actively Confined Concrete

It is well established that lateral confinement of concrete enhances its axial strength and deformability. It is often assumed that, at a same level of confining pressure, the axial compressive stress and strain of fiber reinforced polymer (FRP)-confined concrete at a given lateral strain are the same as those in concrete actively confined concrete. To assess the validity of this assumption, an experimental program relating both types of confinement systems was conducted. 25 FRP-confined and actively confined high-strength concrete (HSC) specimens cast from a same batch of concrete were tested under axial compression. The axial stress-strain and lateral strain-axial strain curves obtained from the two different confinement systems were assessed. The results indicate that, at a given axial strain, lateral strains of actively confined and FRP-confined concretes correspond, when they are subjected to the same lateral confining pressure. However, it is observed that, at these points of intersections on axial strain-lateral strain curves, FRP-confined concrete exhibits a lower axial stress than the actively confined concrete, indicating that the aforementioned assumption is not accurate. The test results indicate that the difference in the axial stresses of FRP-confined and actively confined HSC becomes more significant with an increase in the level of confining pressure.

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The Effect of Confining Pressure on the Mechanical Properties of Sand–Ice Materials

Journal of Glaciology ◽

10.1017/s0022143000031889 ◽

1973 ◽

Vol 12 (66) ◽

pp. 469-481 ◽

Cited By ~ 42

Author(s):

Bernard D. Alkire ◽

Orlando B. Andersland

Keyword(s):

Axial Strain ◽

Triaxial Compression ◽

Confining Pressure ◽

Silica Sand ◽

Creep Tests ◽

Ice Volume ◽

Coulomb Failure ◽

Confining Pressures ◽

Sand Material ◽

Cylindrical Samples

Cylindrical samples containing 0.59 mm to 0.84 mm diameter silica sand at about 97% and 55% ice saturation (the ratio of ice volume to sand pore volume) were tested at a temperature of −12° C in triaxial compression. Both constant axial strain-rate tests and step-stress creep tests provide information on the influence of confining pressure on the shear strength and creep behavior of the sand–ice material. Changes in the degree of ice saturation help show the influence of the ice matrix versus the sand material on the mechanical behavior. Data are discussed in terms of the Mohr–Coulomb failure law and creep theories. It is shown that the cohesive component of strength depends on response of the ice matrix, whereas the frictional component of strength responds in a manner very similar to unfrozen sand tested at high confining pressures. Experimental data show that creep rates decrease exponentially and creep strength increases with an increase in confining pressure.

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Small-strain behavior of frozen sand in triaxial compression

Canadian Geotechnical Journal ◽

10.1139/t95-047 ◽

1995 ◽

Vol 32 (3) ◽

pp. 428-451 ◽

Cited By ~ 29

Author(s):

Glen R. Andersen ◽

Christopher W. Swan ◽

Charles C. Ladd ◽

John T. Germaine

Keyword(s):

High Pressure ◽

Strain Rate ◽

Yield Stress ◽

Axial Strain ◽

Triaxial Compression ◽

Strain Curve ◽

Confining Pressure ◽

Stress Strain ◽

Strain Behavior ◽

Frozen Sand

The stress–strain behavior of frozen Manchester fine sand has been measured in a high-pressure low-temperature triaxial compression testing system developed for this purpose. This system incorporates DC servomotor technology, lubricated end platens, and on-specimen axial strain devices. A parametric study has investigated the effects of changes in strain rate, confining pressure, sand density, and temperature on behavior for very small strains (0.001%) to very large (> 20%) axial strains. This paper presents constitutive behavior for strain levels up to 1%. On-specimen axial strain measurements enabled the identification of a distinct upper yield stress (knee on the stress–strain curve) and a study of the behavior in this region with a degree of precision not previously reported in the literature. The Young's modulus is independent of strain rate and temperature, increases slightly with sand density in a manner consistent with Counto's model for composite materials, and decreases slightly with confining pressure. In contrast, the upper yield stress is independent of sand density, slightly dependent on confining pressure (considered a second order effect), but is strongly dependent on strain rate and temperature in a fashion similar to that for polycrystalline ice. Key words : frozen sand, high-pressure triaxial compression, strain rate, temperature, modulus, yield stress.

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A Strain-Based Percolation Model and Triaxial Tests to Investigate the Evolution of Permeability and Critical Dilatancy Behavior of Coal

Processes ◽

10.3390/pr6080127 ◽

2018 ◽

Vol 6 (8) ◽

pp. 127 ◽

Cited By ~ 6

Author(s):

Dongjie Xue ◽

Jie Zhou ◽

Yintong Liu ◽

Sishuai Zhang

Keyword(s):

Axial Strain ◽

Triaxial Compression ◽

Sudden Change ◽

Volumetric Strain ◽

Confining Pressure ◽

Percolation Model ◽

Triaxial Tests ◽

Transition Behavior ◽

Orthogonal Experiments ◽

Stress Dependent

Modeling the coupled evolution of strain and CH4 seepage under conventional triaxial compression is the key to understanding enhanced permeability in coal. An abrupt transition of gas-stress coupled behavior at the dilatancy boundary is studied by the strain-based percolation model. Based on orthogonal experiments of triaxial stress with CH4 seepage, a complete stress-strain relationship and the corresponding evolution of volumetric strain and permeability are obtained. At the dilatant boundary of volumetric strain, modeling of stress-dependent permeability is ineffective when considering the effective deviatoric stress influenced by confining pressure and pore pressure. The computed tomography (CT) analysis shows that coal can be a continuous medium of pore-based structure before the dilatant boundary, but a discontinuous medium of fracture-based structure. The multiscale pore structure geometry dominates the mechanical behavior transition and the sudden change in CH4 seepage. By the volume-covering method proposed, the linear relationship between the fractal dimension and porosity indicates that the multiscale network can be a fractal percolation structure. A percolation model of connectivity by the axial strain-permeability relationship is proposed to explain the transition behavior of volumetric strain and CH4 seepage. The volumetric strain on permeability is illustrated by axial strain controlling the trend of transition behavior and radical strain controlling the shift of behavior. A good correlation between the theoretical and experimental results shows that the strain-based percolation model is effective in describing the transition behavior of CH4 seepage in coal.

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Experimental Study on the Permeability of Weakly Cemented Rock under Different Stress States in Triaxial Compression Tests

Geofluids ◽

10.1155/2018/9035654 ◽

2018 ◽

Vol 2018 ◽

pp. 1-9 ◽

Cited By ~ 1

Author(s):

Gangwei Fan ◽

Mingwei Chen ◽

Dongsheng Zhang ◽

Zhen Wang ◽

Shizhong Zhang ◽

...

Keyword(s):

Underground Mining ◽

Axial Strain ◽

Triaxial Compression ◽

Confining Pressure ◽

Initial Permeability ◽

Compression Tests ◽

Mining Operations ◽

Stress Strain ◽

Loading And Unloading ◽

Stress States

Mudstone and shaly coarse sandstone samples of Jurassic units in northwestern China were collected to study the seepage mechanism of weakly cemented rock affected by underground mining operations. Samples were studied using seepage experiments under triaxial compression considering two processes: complete stress-strain and postpeak loading and unloading. The results show that permeability variations closely correspond to deviatoric stress-axial strain during the process of complete stress-strain. The initial permeability is 7 times its minimum, contrasting with lesser differentials of initial, peak, and residual permeability. The magnitude of permeability ranges from 10−17 to 10−19 m2, representing a stable water-resisting property, and is 1 to 2 orders lower in mudstone than that in shaly coarse sandstone, indicating that the water-resisting property of the mudstone is much better than that of the shaly coarse sandstone. Permeability is negatively correlated with the confining pressure. In response to this pressure, the permeability change in mudstone is faster than that in shaly coarse sandstone during the process of postpeak loading and unloading. Weakly cemented rock has lower permeability according to the comparison with congeneric ordinary rocks. This distinction is more remarkable in terms of the initial permeability. Analyses based on scanning electron microscope (SEM) observations and mineral composition indicate that the samples are rich in clay minerals such as montmorillonite and kaolin, whose inherent properties of hydroexpansiveness and hydrosliming can be considered the dominant factors contributing to the seepage properties of weakly cemented rock with low permeability.

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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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