scholarly journals Influence of Key Strata on the Gas Downward Leakage Law in Dual-System of Coal Seam

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Feng Du ◽  
Kun Jiao ◽  
Zhanyuan Ma
Keyword(s):  
Coal Seam ◽  
Mining Area ◽  
Key Strata ◽  
Periodic Movement ◽  
Fracture Development ◽  
The Law ◽  
Mining Pressure ◽  
Pathway Formation ◽  
Similar Simulation Test ◽  
Overburden Strata

In Datong mining area, CO and other harmful gases were discharged from the gob in the Jurassic overburden strata to the panel of Carboniferous coal seam. To this end, panel 8309 of Tongxin coal mine in Datong mining area was taken as the engineering background; the change law of CO concentration in the upper corner of the panel and the law of mining pressure were studied through field measurement, and the influence of periodic movement of key strata on the downward leakage law of harmful gases was analyzed. In this paper, the fracture law of the key strata and fracture development characteristics of overburden strata were further studied by the similar simulation test, and the influence of the periodic movement of the key strata on the pathway formation of gas downward leakage was analyzed. The results show that the main cause of harmful gas downward leakage in the Jurassic gob is through the fracture produced by the fracture of the higher key strata. If the higher key strata fractures in the coal mining in the Carboniferous system, through fracture connecting the Jurassic gob above the open-off cut and the upper part of the panel are formed, and effective pathways for gas downward leakage are generated. The fracture and rotation of the higher key strata are accompanied by the formation and disappearance of the effective pathway for gas downward leakage above the panel. Then the periodic change of harmful gas discharging to the panel is caused and consistent with the law of mining pressure.

scholarly journals Repeated Low-Intensity Shock Wave Simulation Experiment for Fracture Development and Propagation of Coal

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Taofeng Xie ◽  
Xiaoting Zhou ◽  
Qingya Wang ◽  
Shuai Cao ◽  
Huiming Cao ◽  
...  
Keyword(s):  
Shock Wave ◽  
Coal Seam ◽  
Simulation Experiment ◽  
Low Intensity ◽  
Wave Simulation ◽  
Microcrack Propagation ◽  
Fracture Development ◽  
Pore Evolution ◽  
The Law ◽  
The Impact

For low-permeability coal seam, the gas extraction rate is relatively low. The repeated low-intensity shock wave can improve the permeability of coal and raise the rate of coal seam gas drainage. A simulation test platform was set up to carry out repeated low-intensity shock wave simulation experiment. Under the effect of repeated low-intensity shock wave, the development process of the macrofracture, pore evolution, and the law of microcrack propagation was analyzed to study the law of coal fracture propagation. Research shows that the expansion of the pore of the coal is made by the development of large, medium, and micropores by the repeated low-strength shock wave. The main contribution of the total pore volume increase comes from the micropore growth. The microcrack of the coal mainly begins to sprout and develops from the telocollinite where the fracture is more developed. With the increase of impact times, the microcracks extend to other components. Under the impact of different times, the fractal dimension of the coal sample increases with the increase in the number and length of cracks.

scholarly journals Study on the Evolution Law of Fracture Field in Full-Mechanized Caving Mining of Double System and Extrathick Coal Seam

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Feng Du ◽  
Wenqiang Wang ◽  
Zhenhua Li
Keyword(s):  
Fracture Surface ◽  
Coal Seam ◽  
Field Measurement ◽  
Decisive Role ◽  
Mine Pressure ◽  
Far Field ◽  
Evolution Law ◽  
Key Strata ◽  
Double System ◽  
Overburden Strata

During the full-mechanized caving mining, the overburden strata in the double system and extrathick coal seam of the Datong mining area are largely damaged. Water and harmful gas in the old goaf may be discharged when overburden fractures evolve to the upper goaf, which poses a major threat to the normal production of the panel. To study the movement of overburden strata and the evolution of fracture field under the full-mechanized caving mining of the double system and extrathick coal seam, panel 8309 of Tongxin mine was taken as the research object; the evolution rule of fracture field in the full-mechanized caving mining of the double system and extrathick coal seam was obtained through field measurement and physical similar simulation. The results show the following: (1) the far-field and near-field key strata play a decisive role in controlling the fracture evolution of overburden strata. When the far-field key strata break and the development height of fractures reaches 220.9 m, panel 8309 is connected with the overburden goaf. (2) Based on the “O-shape circle” theory of mining fracture, with the continuous advance of the panel, the overburden breaks periodically, and a “fracture surface” with a certain angle of 61°–67° can be formed along with the advancing direction of the panel. (3) When the key strata are broken and the development height of fractures reaches the maximum, the fracture surface is formed as the “main fracture surface,” which is the only downward discharge pathway for goaf water and harmful gas. The overall shape fracture surface is “inverted trapezoid” in the upper part and “positive trapezoid” in the lower part. (4) Based on the field measurement of the water level of borehole and the observation of mine pressure, the correctness of the evolution law of the similar simulated fracture field is verified.

Water inflow characteristics of coal seam mining aquifer in Yushen mining area, China

2021 ◽  
Vol 14 (4) ◽  
Author(s):  
Zhao Chunhu ◽  
Jin Dewu ◽  
Wang Qiangmin ◽  
Wang Hao ◽  
Li Zhixue ◽  
...  
Keyword(s):  
Coal Seam ◽  
Mining Area ◽  
Water Inflow ◽  
Seam Mining

scholarly journals Investigation of the kinetics of spontaneous combustion of the major coal seam in Dahuangshan mining area of the Southern Junggar coalfield, Xinjiang, China

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Li Shen ◽  
Qiang Zeng
Keyword(s):  
Particle Size ◽  
High Temperature ◽  
Coal Seam ◽  
Spontaneous Combustion ◽  
Heating Temperature ◽  
Characteristic Temperature ◽  
Mining Area ◽  
Particle Sizes ◽  
Coal Oxidation ◽  
Increasing Temperature

AbstractIn the present paper, with using diverse methods (including the SEM, the XRD, the TPO, the FTIR, and the TGA) , the authors analysed samples of the major coal seam in Dahuangshan Mining area with different particle sizes and with different heated temperatures (from 50 to 800 °C at regular intervals of 50 °C). The results from SEM and XRD showed that high temperature and high number of pores, fissures, and hierarchical structures in the coal samples could facilitate oxidation reactions and spontaneous combustion. A higher degree of graphitization and much greater number of aromatic microcrystalline structures facilitated spontaneous combustion. The results from TPO showed that the oxygen consumption rate of the coal samples increased exponentially with increasing temperature. The generation rates of different gases indicated that temperatures of 90 °C or 130 °C could accelerate coal oxidation. With increasing temperature, the coal oxidation rate increased, and the release of gaseous products was accelerated. The FTIR results showed that the amount of hydroxide radicals and oxygen-containing functional groups increased with the decline in particle size, indicating that a smaller particle size may facilitate the oxidation reaction and spontaneous combustion of coal. The absorbance and the functional group areas at different particle sizes were consistent with those of the heated coal samples, which decreased as the temperature rose. The results from TGA showed that the characteristic temperature T3 declined with decreasing particle size. After the sample with 0.15–0.18 mm particle size was heated, its carbon content decreased, and its mineral content increased, inhibiting coal oxidation. This result also shows that the activation energy of the heated samples tended to increase at the stage of high-temperature combustion with increasing heating temperature.

scholarly journals Study of the Stability Control of the Rock Surrounding Double-Key Strata Recovery Roadways in Shallow Seams

2019 ◽  
Vol 2019 ◽  
pp. 1-21 ◽  
Author(s):  
Cheng Zhu ◽  
Yong Yuan ◽  
Zhongshun Chen ◽  
Zhiheng Liu ◽  
Chaofeng Yuan
Keyword(s):  
Engineering Application ◽  
Stability Control ◽  
Surrounding Rock ◽  
Control Effect ◽  
Pressure Relief ◽  
Support Design ◽  
Key Strata ◽  
Fracture Development ◽  
Surrounding Rock Control ◽  
The Stability

The stability control of the rock surrounding recovery roadways guarantees the safety of the extraction of equipment. Roof falling and support crushing are prone to occur in double-key strata (DKS) faces in shallow seams during the extraction of equipment. Therefore, this paper focuses on the stability control of the rock surrounding DKS recovery roadways by combining field observations, theoretical analysis, and numerical simulations. First, pressure relief technology, which can effectively release the accumulated rock pressure in the roof, is introduced according to the periodic weighting characteristics of DKS roofs. A reasonable application scope and the applicable conditions for pressure relief technology are given. Considering the influence of the eroded area on the roof structure, two roof mechanics models of DKS are established. The calculation results show that the yield load of the support in the eroded area is low. A scheme for strengthening the support with individual hydraulic props is proposed, and then, the support design of the recovery roadway is improved based on the time effects of fracture development. The width of the recovery roadway and supporting parameters is redesigned according to engineering experience. Finally, constitutive models of the support and compacted rock mass in the gob are developed with FLAC3D software to simulate the failure characteristics of the surrounding rock during pressure relief and equipment extraction. The surrounding rock control effects of two support designs and three extraction schemes are comprehensively evaluated. The results show that the surrounding rock control effect of Scheme 1, which combines improved support design and the bidirectional extraction of equipment, is the best. Engineering application results show that Scheme 1 realizes the safe extraction of equipment. The research results can provide a reference and experience for use in the stability control of rock surrounding recovery roadways in shallow seams.

scholarly journals Research on Microscopic Evolution Laws of Sandstone Deformation and Failure Based on the Particle Discrete Element Method

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Zhiwei Cai ◽  
Tongqing Wu ◽  
Jian Lu ◽  
Yue Wu ◽  
Nianchun Xu
Keyword(s):  
Shear Crack ◽  
Rock Fracture ◽  
Confining Pressure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Deformation And Failure ◽  
Fracture Development ◽  
Confining Pressures ◽  
The Law ◽  
Microcrack Growth

The fracture of sandstone is closely related to the condition of internal microcracks and the fabric of micrograin. The macroscopic mechanical property depends on its microscopic structures. However, it is difficult to obtain the law of the microcrack growth under loading by experiments. A series of microscopic sandstone models were established with particle flow code 3D (PFC3D) and based on the triaxial experiment results on sandstones. The experimental and numerical simulations of natural and saturated sandstones under different confining pressures were implemented. We analyzed the evolution of rock deformation and the rock fracture development from a microscopic view. Results show that although the sandstones are under different confining pressures, the law of microcrack growth is the same. That is, the number of the microcracks increases slowly in the initial stage and then increases exponentially. The number of shear cracks is more than the tensile cracks, and the proportion of the shear cracks increases with the increase of confining pressure. The cracking strength of natural and saturated sandstones is 26% and 27% of the peak strength, respectively. Under low confining pressure, the total number of cracks in the saturated sample is 20% more than that of the natural sample and the strongly scattered chain is barely seen. With the increase of the confining pressure, the effect of water on the total number of cracks is reduced and the distribution of the strong chain is even more uniform. In other words, it is the confining pressure that mainly affects the distribution of the force chain, irrespective of the state of the rock, natural or saturated. The research results reveal that the control mechanism of shear crack friction under the different stress states of a rock slope in the reservoir area provides a basis for evaluating the stability of rock mass and predicting the occurrence of geological disasters.

Computational fluid dynamics optimization of gas drainage technology in gas-mining areas

2021 ◽  
pp. 014459872110635
Author(s):  
Wei Zhao ◽  
Wei Qin
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Coal Seam ◽  
Field Tests ◽  
Mining Area ◽  
Engineering Practice ◽  
Horizontal Distance ◽  
Gas Drainage ◽  
Working Face ◽  
Gas Seepage

Coal mining results in strata movement and surrounding rock failure. Eventually, manual mining space will be occupied by the destructed coal rock, making it difficult to conduct field tests of the coal seam to explore gas seepage and transport patterns. Therefore, computational fluid dynamics (CFD) numerical computation is an important tool for such studies. From the aspect of gas pre-drainage, for layer-through boreholes in the floor roadway of the 8,406 working face in Yangquan Mine 5 in China, reasonable layout parameters were obtained by CFD optimization. For effectively controlling the scope of boreholes along coal seam 9 in the Kaiyuan Mine, CFD computation was performed. The results revealed that the horizontal spacing between boreholes should be ≤2 m when a tri-quincuncial borehole layout is used. Optimization of the surface well position layout for the fault structure zone in the Xinjing Mine of the Yangquan mining area indicated that the horizontal distance between the surface well and the fault plane should be <150 m. From the aspect of gas drainage with mining-induced pressure relief, CFD computation was performed for pressure-relieved gas transport in the K8205 working face of Yangquan Mine 3. The results showed that forced roof caving should be used before the overhang length of hard roof reaches 25 m in the K8205 working face to avoid gas overrun. From the aspect of gas drainage from the abandoned gob, surface well control scopes at different surface well positions were computed, and an O-ring fissure zone is proposed as a reasonable scope for the surface well layout. CFD computation has been widely applied to coal and gas co-extraction in the Yangquan mining area and has played a significant role in guiding related gas drainage engineering practice.

scholarly journals Mechanism of Secondary Breakage in the Overlying Strata during Repetitious Mining of an Ultrathick Coal Seam in Design Stage

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Hui Li ◽  
Dongsheng Zhang ◽  
Shuyin Jiang ◽  
Gangwei Fan ◽  
Mengtang Xu
Keyword(s):  
Coal Seam ◽  
Mining Area ◽  
Design Stage ◽  
Mining Method ◽  
Joint Stability ◽  
Mechanical Models ◽  
Physical Simulations ◽  
Research Findings ◽  
New Feature ◽  
Overlying Strata

When designing the mining of an ultrathick coal seam, the laws governing movement in the overlying strata during mining are a fundamental issue based on which several problems are addressed, including determining the mining method and the roadway arrangement, controlling the surrounding strata, and selecting the devices. The present paper considers possible problems related to strata overlying a large mining space subjected to repeated disturbances during the mining of an ultrathick coal seam, including repeatedly broken strata and the existence or inexistence of the structure. The BM coal seam in the No. 2 coal mine of the Dajing mining area in the East Junggar coalfield is studied. Physical simulations are performed on the movements of the overlying strata during slicing mining of the ultrathick coal seam, revealing the new feature of “break-joint stability-instability-secondary breakage” in the overlying strata. Mechanical models are constructed of the secondary breakage of the overlying strata blocks under both static and impact loading, and mechanical criteria are proposed for such breakage. Based on the research findings, methods for controlling the surrounding strata during slicing mining of an ultrathick coal seam are proposed, including increasing the mining rate and designing reasonable heights for the slicing mining.

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