scholarly journals Experimental Study on Damage and Gas Migration Characteristics of Gas-Bearing Coal with Different Pore Structures under Sorption-Sudden Unloading of Methane

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Gang Wang ◽  
Yangyang Guo ◽  
Chang’ang Du ◽  
Lulu Sun ◽  
Zhiyuan Liu ◽  
...  
Keyword(s):  
Axial Strain ◽  
Radial Strain ◽  
Axial Direction ◽  
Gas Migration ◽  
Pore Structures ◽  
Gas Seepage ◽  
Experimental Apparatus ◽  
Methane Sorption ◽  
Seepage Characteristics ◽  
Gas Bearing

Coal and gas outburst is one of the most serious hazards in underground mine operations. In this paper, we explored the damage and gas seepage characteristics of gas-bearing coal samples with different pore structures under methane sorption-sudden unloading conditions using a self-developed experimental apparatus. The results show that (1) the deformation of coal samples can be divided into three stages, namely, pressure-increase-induced compression, sorption-induced expansion, and sudden-unloading-induced deformation or failure stage; (2) with the increase of the number of diffusion pores in the coal sample, the amount of gas sorption gradually increases and the expansion and failure of coal samples become more obvious; (3) in the experiment, the damage of coal samples is mainly along the axial direction and rarely along the radial direction; (4) the radial strain is always greater than the axial strain.

scholarly journals Seepage and Damage Evolution Characteristics of Gas-Bearing Coal under Different Cyclic Loading–Unloading Stress Paths

Processes ◽  
2018 ◽  
Vol 6 (10) ◽  
pp. 190 ◽  
Author(s):  
Qingmiao Li ◽  
Yunpei Liang ◽  
Quanle Zou
Keyword(s):  
Cyclic Loading ◽  
Peak Stress ◽  
Cyclic Loading And Unloading ◽  
Evolution Characteristics ◽  
Three Phase ◽  
Boltzmann Function ◽  
Gas Seepage ◽  
Seepage Characteristics ◽  
Number Of Cycles ◽  
Gas Bearing

The mechanical properties and seepage characteristics of gas-bearing coal evolve with changes in the loading pattern, which could reveal the evolution of permeability in a protected coal seam and allow gas extraction engineering work to be designed by using the effect of mining multiple protective seams. Tests on gas seepage in raw coal under three paths (stepped-cyclic, stepped-increasing-cyclic, and crossed-cyclic loading and unloading) were carried out with a seepage tester under triaxial stress conditions. The permeability was subjected to the dual influence of stress and damage accumulation. After being subjected to stress unloading and loading, the permeability of coal samples gradually decreased and the permeability did not increase before the stress exceeded the yield stage of the coal samples. The mining-enhanced permeability of the coal samples in the loading stage showed a three-phase increase with the growth of stress and the number of cycles and exhibited an N-shaped increase under the stepped-cyclic loading while it linearly increased under the other two paths in the unloading stage. With the increase of peak stress and the accumulation of damage in coal samples, the sensitivity of the permeability of coal samples to stress gradually declined. The relationship between the damage variable and the number of cycles conformed to the Boltzmann function.

Experimental Study of Mechanical and Seepage Characteristics of Two Kinds of Coal Samples

2014 ◽  
Vol 1073-1076 ◽  
pp. 2098-2101
Author(s):  
Wen Pu Li
Keyword(s):  
Coal Sample ◽  
Axial Strain ◽  
Volumetric Strain ◽  
Quadratic Function ◽  
Coal Bed ◽  
Coal Bed Methane ◽  
Intensity Level ◽  
Methane Recovery ◽  
Gas Seepage ◽  
Seepage Characteristics

Mechanical and seepage characteristics of raw coal samples are the most important research contents of enhancing coal bed methane recovery, but the produce of raw coal sample is very difficult. Based on gas seepage instrument, mechanical and seepage characteristics were performed on normal briquette coal samples and coal samples containing gypsum. The results show that it can increase the cohesion and intensity level by adding gypsum in briquette coal. Porosity and permeability of coal containing gypsum is less than ordinary briquette coal sample. Permeability with axial strain curves of two kinds of coal samples can be fitted with a quadratic function well. In expansion stage, volumetric strain of ordinary coal sample is much smaller than the coal samples containing gypsum. The research has an important guiding significance on enhancing coal bed methane recovery and gateway supporting.

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.

Performance of Multifiber Beam Element for Seismic Analysis of Reinforced Concrete Structures

2014 ◽  
Vol 14 (06) ◽  
pp. 1450013 ◽  
Author(s):  
Xuan Huy Nguyen
Keyword(s):  
Reinforced Concrete ◽  
Damage Mechanics ◽  
Seismic Analysis ◽  
Axial Strain ◽  
Nonlinear Behavior ◽  
Bending Moment ◽  
Axial Direction ◽  
Beam Element ◽  
Shaking Table ◽  
Rc Structures

This paper presents a simplified modeling strategy for simulating the nonlinear behavior of reinforced concrete (RC) structures under seismic loadings. A new type of Euler–Bernoulli multifiber beam element with axial force and bending moment interaction is introduced. To analyze the behavior of RC structures in the axial direction, the interpolation of the axial strain is enriched using the incompatible modes method. The model uses the constitutive laws based on plasticity for steel and damage mechanics for concrete. The proposed multifiber element is implemented in the finite element Code_Aster to simulate the nonlinear behavior of two different RC structures. One structure is a building tested on a shaking table; the other is a column subjected to cyclic loadings. The comparison between the simulation and experimental results shows that the performance of this approach is quite good. The proposed model can be used to investigate the behavior of a wider variety of configurations which are impossible to study experimentally.

Mechanical Behavior of Buried Pipeline Crossing Thaw Settlement Zone

2021 ◽  
Author(s):  
Rui Xie ◽  
Prof. Jie Zhang
Keyword(s):  
Mechanical Behavior ◽  
Axial Strain ◽  
Compressive Strain ◽  
High Stress ◽  
Axial Direction ◽  
Soil Parameters ◽  
Buried Pipeline ◽  
Obvious Effect ◽  
Thaw Settlement ◽  
Pipeline Crossing

Abstract Thaw settlement is one of main reason caused pipeline failure crossing cold region. Mechanical behavior of buried pipeline crossing thaw settlement zone is investigated. Effects of pipeline and soil parameters on the buried pipeline were discussed. The results show that the high stress area and the max axial strain of the pipeline is at the edge of the thaw settlement zone. The upper surface of the pipeline is tensile strain, while the lower surface is compressive strain. The max ovality of pipeline near the edge of thaw settlement zone tends to oval. The pipeline axial strain, ovality and displacement decreases with the increasing of pipeline wall thickness, while the change of high stress area is not obvious. The high stress area and ovality decrease with the increasing of pipeline diameter, while the high stress area is expanded along the axial direction, but axial strain decreases slightly. The high stress area, axial strain, ovality and displacement of pipeline decrease with the buried depth increases. With the internal pressure increases, the stress and axial strain of pipeline increase, but the ovality decreases. The soil`s elasticity modulus has no obvious effect on pipeline`s stress, axial strain and displacement, but it can affect ovality slightly.

scholarly journals Failure and Seepage Characteristics of Gas-Bearing Coal under Accelerated Loading and Unloading Conditions

2019 ◽  
Vol 9 (23) ◽  
pp. 5141
Author(s):  
Zhang ◽  
Wang ◽  
Du ◽  
Lou ◽  
Wang
Keyword(s):  
Confining Pressure ◽  
In Situ Stress ◽  
Permeability Evolution ◽  
Permeability Model ◽  
Significant Control ◽  
Gas Dynamic ◽  
Working Face ◽  
Loading And Unloading ◽  
Seepage Characteristics ◽  
Gas Bearing

In actual mining situations, the advancing speed of the working face is usually accelerated, which may affect the failure and seepage characteristics of gas-bearing coal, and may even induce dynamic disasters. In order to discover the effects of such accelerated advancement of the working face, an experimental study on the failure and seepage characteristics of gas-bearing coal under accelerated loading and unloading conditions was carried out in this work. The results showed that the energy release was more violent and impactful under accelerated loading and unloading paths. The time required for the failure of the sample was significantly shortened. After being destroyed, the breakup of the sample was more severe, and the magnitude of the permeability was greater. Accordingly, the acceleration of the loading and unloading had significant control effects on the failure and permeability of coal and it showed a significant danger of inducing coal and gas dynamic disasters. Meanwhile, the degree of influence of the acceleration on the coal decreased with an increase in the gas pressure and increased significantly with an increase in the initial confining pressure. It was found that for a deep high-gas mine, the accelerated advancement of the working face under a high in situ stress condition would greatly increase the risk of coal and gas dynamic disasters. Then, the permeability evolution model of gas-bearing coal in consideration of changes in the loading and unloading rates was theoretically established in this work, and this permeability model was validated by experimental data. The permeability model was found to be relatively reasonable. In summary, the effects of accelerated loading and unloading on the failure and seepage characteristics of gas-bearing coal were obtained through a combination of experimental and theoretical studies, and the intrinsic relationship between the accelerated advancement of the working face and the occurrence of coal and gas dynamic disasters was discovered in this work.

scholarly journals Effect of matching relation of multi-scale, randomly distributed pores on geometric distribution of induced cracks in hydraulic fracturing

2020 ◽  
Vol 38 (6) ◽  
pp. 2436-2465
Author(s):  
Peihuo Peng
Keyword(s):  
Physical Properties ◽  
In Situ Stress ◽  
Reservoir Rock ◽  
Particle Model ◽  
Bonded Particle Model ◽  
Multi Scale ◽  
Pore Structures ◽  
Fracturing Fluids ◽  
Seepage Characteristics

Reservoir rock contains many multi-scale, unevenly distributed pores, and the pore structures of shale in different reservoirs and geological environments vary greatly. Because the seepage velocity and pressure field are related to the pore spatial variations, the inhomogeneity of the seepage is superimposed on the anisotropy of the rock’s physical properties, which will affect the distribution of the induced cracks. A method for calculating the pore size in the bonded particle model, based on Delaunay triangulation, is proposed. A modeling approach capable of simulating the multi-scale pore distribution of actual rock is presented based on the proposed method. To understand how microcracks connect micropores in the process of fracturing, several bonded particle model samples with different pore structures were established, and numerical experiments were conducted based on the coupling calculation of the discrete seepage algorithm and discrete element method. The focus of this study was on the interactions between the distribution characteristics of multi-scale pores, the specific physical properties of the fracturing fluid, and the distribution differences of the induced cracks caused by the special seepage characteristics when using different fracturing fluids. The numerical results showed that the advantages of supercritical CO2 fracturing are maximized in deep reservoirs (high in-situ stress) and that a suitable in-situ stress condition is required (i.e. a stress ratio close to 1).

Experimental Study of Short-Term Creep Characteristics Base on Step Loading-Unloading Method for Hard Rock

2013 ◽  
Vol 774-776 ◽  
pp. 86-93
Author(s):  
Fu Jun Zhang ◽  
Chuan Xiao Liu
Keyword(s):  
Linear Regression ◽  
Axial Strain ◽  
Radial Strain ◽  
Strain Curve ◽  
Regression Function ◽  
Nonlinear Creep ◽  
Linear Regression Function ◽  
Term Creep ◽  
Sandstone Specimen ◽  
Short Term Creep

Based on experimental results of uniaxial compression and short-term creep using 8-step loading-unloading method, fine sandstone specimen, which lower creep limit is 27MPa, present typical brittle breakage properties of hard rock. The correlative coefficients of linear regression function for isochronous stress-strain curve are all higher than 0. 92, and the ratio of long-term strength to instantaneous strength reaches 94. 39%，which indicate that the whole creep of fine sandstone specimen is weak. The average correlative coefficients of linear regression function for isochronous stress- axial strain curve are 3. 92% higher than that of average correlative coefficients of linear regression function for isochronous stress- radial strain curve, so nonlinear creep property of the fine sandstone specimen in axial direction is correspondingly weaker than that in radial direction. Negative Gauss distribution can be applied collectively to nonlinear creep of fine sandstone specimen, which has obvious time effect.With increasing loading, the reduction degrees of average correlative coefficients of linear fitting functions of isochronous stress-axial strain curve and isochronous stress-radial strain curve are 0. 97% and 0. 67% respectively, which indicates the linear correlation decreases commonly. Thus, the degree of nonlinear creep for fine sandstone specimen increases along with loading stress with obvious stress effect.

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