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

2018 ◽  
Vol 5 (7) ◽  
pp. 180558 ◽  
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.

scholarly journals Deformation Failure and Gas Seepage of Raw Coal in Alternate Loading and Unloading by Stages

2021 ◽  
Author(s):  
Bang-an Zhang ◽  
Yang yushun
Keyword(s):  
Axial Stress ◽  
Axial Strain ◽  
Radial Strain ◽  
Confining Pressure ◽  
Change Rate ◽  
Initial Stage ◽  
Strain Change ◽  
Loading And Unloading ◽  
Unit Stress ◽  
Unloading Confining Pressure

Abstract In this paper, the cyclic loading and unloading confining pressure tests of raw coal samples were carried out by using the "Triaxial seepage test device of thermal fluid solid of coal and rock" developed by Chongqing University. The conclusions are as follows: (1) The axial strain change rate ε1´, the radial strain change rate ε3´ and the permeability change rate k´ under unit stress state are used to represent the sensitivity of axial stress and confining pressure to deformation and permeability characteristics of samples under unit stress state. (2) At the initial stage of unloading the confining pressure, the confining pressure has a greater influence on the permeability of the sample. At the initial stage of loading confining pressure, the confining pressure has a greater influence on the radial strain of the specimen. During the subsequent loading and unloading process, the confining pressure of loading and unloading has a greater influence on the permeability of the sample, and a smaller influence on the axial strain. The loading axial stress has a greater influence on the axial strain of the sample, and a smaller influence on the permeability of the sample. (3) When the axial stress is constant, the increase range of sample permeability increases with the increase of unloading confining pressure range, and the decreasing range of sample permeability increases with the increase of loading confining pressure range, and the increase range of sample permeability under unloading confining pressure is higher than that under increasing confining pressure. (4) In the process of loading axial stress and loading confining pressure, the permeability of samples decreases nonlinearly with the increase of principal stress difference, while the permeability of samples increases nonlinearly with the decrease of principal stress difference in the process of unloading confining pressure.

scholarly journals Experimental Study on Mechanics and Permeability Properties of Water-Bearing Raw Coal Samples Under In-Situ Stress

2019 ◽  
Vol 9 (12) ◽  
pp. 2549
Author(s):  
Zhang ◽  
Wang ◽  
Wang ◽  
Zhang
Keyword(s):  
Axial Strain ◽  
Radial Strain ◽  
Quadratic Function ◽  
Confining Pressure ◽  
In Situ Stress ◽  
Peak Strain ◽  
Permeability Characteristics ◽  
Loading And Unloading ◽  
Unloading Confining Pressure

In this paper, we investigated the mechanical and permeability characteristics ofwater-bearing raw coal samples under in-situ stress, and came to some conclusions, as follows: thepeak strength and peak axial strain of samples gradually decrease with the increase of watercontent. Under the same stress condition, the higher the water content is, the lower the axial strainand radial strain will be. The peak strength and peak strain of the sample both decrease with thewater content as a quadratic function. During the post-peak loading and unloading process, withthe increase of the number of cycles of loading and unloading, the radial strain decrement andincrement of the raw coal sample gradually decrease after loading and unloading confiningpressure. The permeability of samples gradually decreases with the loading confining pressure,and the permeability of the sample gradually increases with the unloading confining pressure. Thepermeability of coal samples increases volatility with the increase of axial strain, and the fittedsample permeability and effective stress are subject to the ExpDec1 function distribution.

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

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.

Experimental Investigation of the Influence of the Adsorption Gas on the Permeability Characteristics of the Coal Containing Gas

2012 ◽  
Vol 616-618 ◽  
pp. 190-196
Author(s):  
Deng Ke Wang ◽  
Jian Ping Wei ◽  
Le Wei ◽  
Heng Jie Qin
Keyword(s):  
Coal Sample ◽  
Gas Adsorption ◽  
Triaxial Compression ◽  
Axial Loading ◽  
Experimental System ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Permeability Characteristics ◽  
Gas Seepage ◽  
Loading Case

A large number of laboratory experiments on the gas seepage characteristics by the self-developed gas-bearing coal triaxial compression experimental system and conducts the comparative analysis of the similarities and differences of the permeability among CO2, CH4 and N2. The results show that given the condition of constant gas pressure, the permeability of the coal sample decreases with the increase of the confining pressure; under the constant confining pressure, the permeability of the coal sample decreases with the increase of the gas pressure; gases of different adsorbabilities have different permeabilities. The stronger the gas adsorption is, the worse its permeability will be; in the axial loading case, the permeabilities of different gases all reduce firstly and increase afterward, showing the generally V-shaped variation law. The results are of certain theoretical values on the in-depth understanding of the migration law of the gas in coal seams.

scholarly journals Experimental Study on Mechanical Properties and Seepage Laws of Raw Coal under Variable Loading and Unloading Rates

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Kangwu Feng ◽  
Kequan Wang ◽  
Dongming Zhang ◽  
Yushun Yang
Keyword(s):  
Axial Stress ◽  
Axial Strain ◽  
Radial Strain ◽  
High Sensitivity ◽  
Confining Pressure ◽  
Variable Loading ◽  
Axial Pressure ◽  
Unloading Rate ◽  
Loading And Unloading ◽  
Seepage Characteristics

This manuscript studied the effects of variable axial pressure loading rate and variable confining pressure unloading rate on the deformation behavior and seepage characteristics of raw coal under alternate loading and unloading of axial pressure and confining pressure. It believed that as axial stress increases, axial strain ε 1 decreases, radial strain ε 3 increases, and permeability k decreases, and ε 1 ′ , ε 3 ′ , and k ′ increase when confining pressure is decreases. With the loading of axial stress and the unloading of confining pressure, the variation amplitudes of ε 1 ′ , ε 3 ′ , and k ′ values reduce gradually. During axial stress loading, the rise in the amplitude of ε 1 is larger than that of ε 3 and the reduction in the amplitude of k , indicating that ε 1 is more sensitive to axial stress than ε 3 and k . During unloading of confining pressure, the increase rate of ε 3 is larger than that of ε 1 and k ; also, ε 3 showed a high sensitivity to confining pressure. In the stage of axial stress loading and confining pressure unloading, the evolution law of deformation and permeability parameters is basically consistent with the change in loading and unloading rate.

scholarly journals Experimental Study on the Deformation and Permeability Characteristics of Raw Coal under the Coupling Effect of Confining Pressure and Pore Pressure

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Kangwu Feng ◽  
Kequan Wang ◽  
Yushun Yang
Keyword(s):  
Elastic Modulus ◽  
Pore Pressure ◽  
Coupling Effect ◽  
Axial Strain ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Peak Strength ◽  
Permeability Evolution ◽  
Permeability Characteristics ◽  
Deformation Properties

The effects of confining pressure and pore pressure on the deformation and permeability characteristics of raw coal are studied experimentally. The deformation properties of raw coal by fracture and its permeability evolution laws under the coupling effect of confining pressure and pore pressure were further studied using a tri-axial servo-controlled seepage system for thermo-fluid-solid coupling of methane-bearing coal. The effects of confining pressure and gas pressure on the strength, elastic modulus, and permeability of raw coal were also analyzed. From the results, it was observed that rise in the confining pressure results in reduction of the initial permeability of raw coal and simultaneously increase its strength which results in higher axial deformation upon failure. Rise in gas pressure would increase the permeability and axial strain of raw coal on the whole and reduce its peak strength. Permeability first decreased and then increased during the loading of deviator stress, following a “V-shaped” change pattern. The results of sensitivity analysis indicated that confining pressure more significantly affected the peak strength and elastic modulus than gas pressure, while the gas pressure more significantly affected the permeability of the material than its confining pressure.

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

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Linna Sun ◽  
Liming Zhang ◽  
Yu Cong ◽  
Yaduo Song ◽  
Keqiang He
Keyword(s):  
Shear Failure ◽  
Axial Stress ◽  
Confining Pressure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Confining Pressures ◽  
Tension Cracks ◽  
Trial And Error Method ◽  
Unloading Confining Pressure ◽  
Fracturing Mechanism

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.

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

2014 ◽  
Vol 919-921 ◽  
pp. 29-34 ◽  
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.

Evaluation of Stress-Controlled Permeability of Coal Fractures - A Laboratory Study

2013 ◽  
Vol 734-737 ◽  
pp. 703-708
Author(s):  
Yi Dong Cai ◽  
Da Meng Liu ◽  
Yan Bin Yao ◽  
Bai Ren Zhang ◽  
Jun Qian Li ◽  
...  
Keyword(s):  
Elastic Deformation ◽  
Axial Stress ◽  
Fractal Dimensions ◽  
Confining Pressure ◽  
Control Factor ◽  
Type I ◽  
Permeability Characteristics ◽  
Linear Elastic ◽  
Variable Permeability ◽  
Nonlinear Elastic

Experiments on coal permeability with saturated water under tri-axial stress were conducted. The relationship between stress and permeability under tri-axial stress was analyzed on the rock mechanical experimental rig (GAW-2000). After the experiments on permeability, the fracture characteristics were researched by X-ray computerized tomography, which shows that the bituminous coal normally has high fractal dimensions (generally over 1.8) and wide aperture. The results for permeability reveal that bituminous coals always have variable permeability characteristics under incremental axial stress due to its inherent fracture features. It can be divided into two types: type I, at the linear and nonlinear elastic deformation and peak stage, the permeability keeps rising, which is represented by FYGY8 #. The main control factor of permeability should be related to coal microfractures and coal compositions. Type II, which is represented by sample YCLZ2#, in the initial linear elastic stage, there is a decrease trend in the permeability performance, and then permeability gradually rise when it comes into the stage of nonlinear elastic deformation. The permeability will keep go down after coal becomes soften under the action of confining pressure, compaction.

Study on Mechanical Property of Structural Damaged Expansive Soil with CT-Triaxial Shear Test

2012 ◽  
Vol 599 ◽  
pp. 811-814
Author(s):  
Lang Jing Shi ◽  
Xian Li ◽  
Zhen Peng ◽  
Shi Ji Wang ◽  
Fan Wu
Keyword(s):  
Mechanical Property ◽  
Axial Stress ◽  
Axial Strain ◽  
Expansive Soil ◽  
Confining Pressure ◽  
Ct Images ◽  
Shear Tests ◽  
Triaxial Shear Test ◽  
Damage Area ◽  
Damage Degree

A series of CT-triaxial shear tests were conducted on expancive soil specimens under controlled suction and confining pressure as 50kPa and 100kPa. The derivative and axial stress in each stage and CT images of inner structure of specimens were obtained .The results show that the different damage location and damage degree on expansive soil samples have different effect on soil mechanical property. The deviatoric stress of smaller damage area sample is larger than of bigger damage area specimen when the damage locates at the same place. The deviatoric strain is independent of the damage degree of samples. The CT images show that with the axial strain increasing, the fissures in soil close gradually, the density of soil increases, and the deformation of samples gets larger with the increase of confining pressure.

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