scholarly journals Mechanical Behavior and Permeability Evolution of Coal under Different Mining-Induced Stress Conditions and Gas Pressures

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2677
Author(s):  
Zetian Zhang ◽  
Ru Zhang ◽  
Zhiguo Cao ◽  
Mingzhong Gao ◽  
Yong Zhang ◽  
...  
Keyword(s):  
Triaxial Compression ◽  
Volumetric Strain ◽  
Coal Mass ◽  
Gas Pressure ◽  
Stress Conditions ◽  
Permeability Evolution ◽  
Compression Tests ◽  
Induced Stress ◽  
Conventional Triaxial Compression ◽  
Gas Pressures

The gas permeability and mechanical properties of coal, which are seriously influenced by mining-induced stress evolution and gas pressure conditions, are key issues in coal mining and enhanced coalbed methane recovery. To obtain a comprehensive understanding of the effects of mining-induced stress conditions and gas pressures on the mechanical behavior and permeability evolution of coal, a series of mining-induced stress unloading experiments at different gas pressures were conducted. The test results are compared with the results of conventional triaxial compression tests also conducted at different gas pressures, and the different mechanisms between these two methods were theoretically analyzed. The test results show that under the same mining-induced stress conditions, the strength of the coal mass decreases with increasing gas pressure, while the absolute deformation of the coal mass increases. Under real mining-induced stress conditions, the volumetric strain of the coal mass remains negative, which means that the volume of the coal mass continues to increase. The volumetric strain corresponding to the peak stress of the coal mass increases with gas pressure in the same mining layout simulation. However, in conventional triaxial compression tests, the coal mass volume continues to decrease and in a compressional state, and there is no obvious deformation stage that occurs during the mining-induced stress unloading tests. The theoretical and experimental analyses show that mining-induced stress unloading and gas pressure changes greatly impact the deformation, failure mechanism and permeability enhancement of coal.

scholarly journals Study on the Permeability Evolution Model of Mining-Disturbed Coal

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Hengyi Jia ◽  
Delong Zou
Keyword(s):  
Axial Stress ◽  
Triaxial Compression ◽  
Strain Curve ◽  
Stress Path ◽  
Coal Mass ◽  
Coal Bed ◽  
Permeability Evolution ◽  
Conventional Triaxial Compression ◽  
Deformation Stages ◽  
Triaxial Creep

Coal permeability plays an important role in the simultaneous exploitation of coal and coal-bed methane (CBM). The stress of mining-disturbed coal changes significantly during coal mining activities, causing damage and destruction of the coal mass, ultimately resulting in a sharp increase in permeability. Conventional triaxial compression and permeability tests were conducted on a triaxial creep-seepage-adsorption and desorption experimental device to investigate the permeability evolution of mining-disturbed coal. The permeability evolution models considering the influence of the stress state and stress path on the fracture propagation characteristics were established based on the permeability difference in the deformation stages of the coal mass. The stress-strain curve of the coal was divided into an elastic stage, yield stage, and plastic flow stage. As the axial stress increased, the permeability decreased and then increased, and the curve’s inflection point corresponded to the yield point. The permeability models exhibited a good agreement with the experimental data and accurately reflected the overall trends of the test results. The results of this study provide a theoretical basis for coal mine disaster prevention and the simultaneous exploitation of coal and CBM.

scholarly journals Permeability evolution of unloaded coal samples at different loading rates

2014 ◽  
Vol 18 (5) ◽  
pp. 1497-1504 ◽  
Author(s):  
Ze-Tian Zhang ◽  
Zhang Ru ◽  
Jian-Feng Liu ◽  
Xiao-Hui Liu ◽  
Jia-Wei Li
Keyword(s):  
Triaxial Compression ◽  
Axial Loading ◽  
Peak Stress ◽  
Initial Permeability ◽  
Differential Method ◽  
Permeability Evolution ◽  
Compression Tests ◽  
Evolution Law ◽  
Loading Rates ◽  
Conventional Triaxial Compression

As coal mass is often at unloading status during mining process, it is of great significance to push on the research on permeability evolution of unloaded coal samples at different loading rates. A series of triaxial unloading experiments were conducted for initially intact coal samples using an improved rock mechanics testing system, and the permeability was continuously measured by the constant pressure differential method for methane. Permeability evolution law of unloaded coal samples and the influence mechanism of loading rates on that were studied. The results of triaxial unloading experiments indicate that the permeability of coal samples increases throughout the whole testing process without a descent stage, which is different from the permeability evolution law in conventional triaxial compression tests. The maximum permeability of unloaded coal sample, which is 4 to 18 times to its initial permeability, often appears before reaching the peak stress and increases with the decrease of axial loading rate. Stress state corresponding to the surge point of permeability of the unloaded coal samples is also discussed.

scholarly journals The influence of particle breakage on stress-dilatancy relationship for granular soils

2019 ◽  
Vol 92 ◽  
pp. 09004 ◽  
Author(s):  
Zenon Szypcio
Keyword(s):  
Internal Energy ◽  
Stress Level ◽  
Triaxial Compression ◽  
Volumetric Strain ◽  
Stress Path ◽  
State Theory ◽  
Particle Breakage ◽  
Compression Tests ◽  
Particle Crushing ◽  
Soil Gradation

The influence of particle breakage on soil behaviour is important from theoretical and practical perspectives. Particle breakage changes the internal energy in two ways. First, internal energy is consumed for particle crushing and second, the internal energy changes because of additional volumetric strain caused by particle crushing. These two effects may be quantified by use of Frictional State Theory. The analysed drained triaxial compression tests of Toyoura sand, gravel and Dog's Bay sand at different stress level and stress path revealed that the effect of particle breakage is a function of soil gradation, strength of soil grains, stress level and stress path.

Effect of ageing on stiffness of very loose sand

2002 ◽  
Vol 39 (1) ◽  
pp. 149-156 ◽  
Author(s):  
J A Howie ◽  
T Shozen ◽  
Y P Vaid
Keyword(s):  
Soil Structure ◽  
Stress Ratio ◽  
Triaxial Compression ◽  
High Stress ◽  
Volumetric Strain ◽  
Compression Tests ◽  
Close Attention ◽  
Stress Ratios ◽  
Creep Modulus ◽  
Triaxial Compression Tests

The paper presents the results of laboratory triaxial compression tests to study the stiffness of very loose Fraser River sands. The stiffness has been shown to be very dependent on the time of confinement prior to shearing and the stress ratio at which the sample is aged. Higher stress ratios resulted in very low initial moduli with no ageing, but the moduli increased by several hundred percent during the first 1000 min of ageing. For ageing at a stress ratio of 1.0 (i.e., isotropic ageing), the initial moduli were higher than those for ageing at high stress ratios, but the stiffness increased by only about 60% during the first 1000 min of ageing. The rate of stiffness increase was approximately linear with the logarithm of time up to ageing times of 10 000 min (>1 week). Ageing at any stress ratio resulted in reduced contractive volumetric strain during subsequent shearing, reflecting a change in soil structure during ageing. The dεv /dεa ratio under triaxial compression loading decreased as the ageing stress ratio increased. The results suggest that close attention must be paid to the age of laboratory samples prepared to study the stress–strain response of sands at strains up to about 0.1%, particularly in studies on loose sand.Key words: sands, ageing, creep, modulus.

scholarly journals Stress–dilatancy of gravel for triaxial compression tests

2018 ◽  
Vol 50 (2) ◽  
pp. 119-128 ◽  
Author(s):  
Zenon Szypcio
Keyword(s):  
Shear Strain ◽  
Triaxial Compression ◽  
Volumetric Strain ◽  
State Theory ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Stress Strain ◽  
Characteristic Points ◽  
Triaxial Compression Tests

Abstract The stress–plastic dilatancy relationships for gravel are analyzed based on drained triaxial tests experiments described in literature. For this, Frictional State Theory is used. The characteristic points and stages of shearing may be defined from the analysis of η–Dp relationship. The characteristic points and stages of shearing cannot be identified from ordinary stress–strain, volumetric strain–shear strain relationships that are shown in literature.

scholarly journals A Nonlinear Strength Criterion for Frozen Sulfate Saline Silty Clay with Different Salt Contents

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Yanhu Zhao ◽  
Yuanming Lai ◽  
Jing Zhang ◽  
Chong Wang
Keyword(s):  
Triaxial Compression ◽  
Strength Criterion ◽  
Experimental Results ◽  
Saline Soils ◽  
Silty Clay ◽  
Compression Tests ◽  
Frozen Soils ◽  
Conventional Triaxial Compression ◽  
Confining Pressures ◽  
Pressure Melting

It has been proven that the mechanical properties of frozen saline soils are different from frozen soils and unfrozen saline soils. In this paper, in order to study the effects of the salt contents on the strength characteristics of frozen soils, a series of conventional triaxial compression tests are carried out for frozen saline silty clay with Na2SO4 contents 0.0, 0.5, 1.5, and 2.5% under confining pressures from 0 MPa to 18 MPa at −6°C, respectively. The experimental results show that the strength of frozen saline silty clay presents obvious nonlinearity, the strength of frozen saline silty clay increases with increasing confining pressures at first, but with a further increase in confining pressures, the strength decreases because of pressure melting and crushing phenomena under high confining pressures, and salt contents have an important influence on strength of frozen saline silty clay. A strength criterion is proposed on the basis of the experimental results. The strength criterion could well reflect the nonlinear strength characteristic of frozen saline silty clay and the influence of salt contents on frozen saline silty clay.

Effect of particle size and strain conditions on the strength of crushed basalt

1983 ◽  
Vol 20 (4) ◽  
pp. 706-717 ◽  
Author(s):  
Mosaid Al-Hussaini
Keyword(s):  
Particle Size ◽  
Stress Level ◽  
Level Density ◽  
Triaxial Compression ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Strain Diagram ◽  
Compression Tests ◽  
Cohesionless Soils ◽  
Lower Shear

This paper describes the results of an investigation carried out to study the influence of particle size, stress level, density, method of consolidation, and strain conditions on the strength and compressibility of crushed basalt. All specimens were prepared at medium or high density, consolidated isotropically or under K0 consolidation, and sheared under effective confining pressure ranging from 443 to 2297 kPa. The material used in the test program had a straight line grain size distribution with maximum particle size ranges from 0.63 to 76.2 mm and minimum particle size equivalent to No. 30 U.S. standard sieve size:The tests indicated that an increase in the particle size (i.e., gradation) increases the strength and decreases the axial and the volumetric strain at failure. The study indicated further that the crushed basalt under triaxial compression has a lower shear strength than when sheared under plane strain conditions. Particles crushed were significantly influenced by the stress level and gradation and to a lesser degree by density of material. Keywords: cohesionless soils, density (mass/volume), shear tests, stress–strain diagram, compression tests, rockfill dams.

Experimental Study on Evolution of Rock Damage Rule in the Condition of Conventional Three Axis Compression

2014 ◽  
Vol 670-671 ◽  
pp. 432-436
Author(s):  
Bing He
Keyword(s):  
Damage Mechanics ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Volumetric Strain ◽  
Continuum Damage Mechanics ◽  
Continuum Damage ◽  
Conventional Triaxial Compression ◽  
Axis Compression ◽  
Plastic Volumetric Strain ◽  
Damage Rule

Based on continuum damage mechanics, by defining the initial and critical damage value, because of the plastic volumetric strain of the specimen, we established the calculation methods of the rock specimen’s damage value. Through the conventional triaxial compression test of the shale, we find that damage value D changes as axial strain changes during compression, and summarizes its variation.

Thermodynamic Properties of Soft Sedimentary Rock in Geotechnical Engineering

2012 ◽  
Vol 170-173 ◽  
pp. 687-691 ◽  
Author(s):  
Jing Yin Wang ◽  
Fang Liu
Keyword(s):  
Thermodynamic Properties ◽  
Sedimentary Rock ◽  
Geotechnical Engineering ◽  
Triaxial Compression ◽  
Soft Rock ◽  
Compression Tests ◽  
Creep Tests ◽  
Oil Drilling ◽  
Viscoplastic Model ◽  
Conventional Triaxial Compression

In geotechnical engineering such as supporting of deep and soft rock roadway ,oil drilling , and construction of military underground defensive facility, thermodynamic properties of soft sedimentary rock has guiding significances .The study of the thermal constitutive behavior of rock under temperature has been done for many years, and many achievement have been got on this issue. In this paper, some experimental researches on the thermo-mechanical characteristics of soft sedimentary rock have been presented. Some test results have been simulated with a thermo-elasto-viscoplastic model. The results show that the proposed thermo-elasto-viscoplastic model reflects the visco-elastoplastic properties of rock，and can describe the thermo-mechanical behaviors of soft shale rocks in not only drained conventional triaxial compression tests but also drained triaxial creep tests. So it can be used for analysis of theology and stability of rock engineering.

Plasticity of Ice and Sand-Ice Systems

1975 ◽  
Vol 97 (2) ◽  
pp. 479-484 ◽  
Author(s):  
Leonard L. Smith ◽  
J. B. Cheatham
Keyword(s):  
Triaxial Compression ◽  
Plasticity Theory ◽  
Compression Tests ◽  
Loading Rates ◽  
Conventional Triaxial Compression ◽  
Confining Pressures ◽  
Von Mises ◽  
Comparison Of The Results ◽  
Force Displacement ◽  
Triaxial Compression Tests

The experimental deformation of ice and sand-ice systems is compared with predictions based upon plasticity theory. Properties of the materials were determined under various temperatures, confining pressures, and loading rates using conventional triaxial compression tests. Samples were indented at atmospheric pressure using flat punches and sharp wedges at two loading rates and calculated force-displacement relationships were determined for the von Mises, coulomb, and parabolic yield conditions. Comparison of the results of the experiments with the computations indicates that the force-displacement relationships for ice and sand-ice samples can be approximated using plasticity theory.

Sign in / Sign up

Export Citation Format

Share Document