scholarly journals Floor failure depth of upper coal seam during close coal seams mining and its novel detection method

2017 ◽  
Vol 36 (5) ◽  
pp. 1265-1278 ◽  
Author(s):  
Wei Zhang ◽  
Dongsheng Zhang ◽  
Dahong Qi ◽  
Wenmin Hu ◽  
Ziming He ◽  
...  
Keyword(s):  
Stress Distribution ◽  
Coal Seam ◽  
Mechanical Model ◽  
Coal Pillar ◽  
Coal Seams ◽  
Geological Conditions ◽  
Floor Failure ◽  
Calculation Results ◽  
Failure Depth ◽  
Close Coal Seams

The primary problem needed to be solved in mining close coal seams is to understand quantitatively the floor failure depth of the upper coal seam. In this study, according to the mining and geological conditions of close coal seams (#10 and #11 coal seams) in the Second Mining Zone of Caocun Coal Mine, the mechanical model of floor failure of the upper coal seam was built. Calculation results show that the advanced abutment pressure caused by the mining of the upper coal seam, resulted in the floor failure depth with a maximum of 26.1 m, which is 2.8 times of the distance between two coal seams. On this basis, the mechanical model of the remaining protective coal pillar was established and the stress distribution status under the remaining protective coal pillar in the 10# coal seam was then theoretically analysed. Analysis results show that stress distribution under the remaining protective coal pillar was significantly heterogeneous. It was also determined that the interior staggering distance should be at least 4.6 m to arrange the gateways of the #209 island coalface in the lower coal seam. Taken into account a certain safety coefficient (1.6–1.7), as well as reducing the loss of coal resources, the reasonable interior staggering distance was finally determined as 7.5 m. Finally, a novel method using radon was initially proposed to detect the floor failure depth of the upper coal seam in mining close coal seams, which could overcome deficiencies of current research methods.

scholarly journals Modeling the Spatial and Temporal Evolution of Stress during Multiworking Face Mining in Close Distance Coal Seams

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Yong Zhang ◽  
Jinkun Yang ◽  
Jiaxuan Zhang ◽  
Xiaoming Sun ◽  
Chen Chen ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Stress Distribution ◽  
Temporal Evolution ◽  
Coal Pillar ◽  
Coal Seams ◽  
Geological Conditions ◽  
Coal Pillars ◽  
The Stability ◽  
Close Distance ◽  
Close Distance Coal Seams

Mining in close distance coal seams (CDCSs) is frequently associated with engineering disasters because of the complicated nature of stress distribution within CDCSs. In order to establish a layout of a roadway to minimize the occurrence of disasters associated with mining CDCS, here the spatial and temporal evolution of stress distribution during the multiworking face mining of a CDCS was explored through numerical simulation based on the engineering and geological conditions of the Nantun Coal Mine. The numerical simulation results indicate that, after the extraction of adjacent multiple working faces, the spatial distribution of stress can be characterized with areas of increased, reduced, and intact stress. The superposed stress of inclined seams that are very close to each other propagates through coal pillars in the bottom floor, and this propagation follows neither the line along the axis of the coal pillar nor the line perpendicular to the direction of the floor. It instead propagates along a line angled with the axis of the coal pillar. The roadway can be arranged in the area with reduced stress, to improve its the stability. Based on the computed spatial and temporal evolution of stress, an optimized layout of roadway was proposed. This layout features a reasonable interval between the mining roadway and a minimal proportion of increased stress areas along the mining roadway and is aligned with geological structures.

scholarly journals Research on Characteristic Recognition and Dangerous Prevention While Mining through Collapse Column of Pansan Minefield,China

2021 ◽  
Author(s):  
Haitao Xu ◽  
hui yang ◽  
Wenbin Sun ◽  
Lingjun Kong ◽  
Peng Zhang
Keyword(s):  
Coal Seam ◽  
Water Inrush ◽  
Coal Pillar ◽  
Simulation Software ◽  
Coal Seams ◽  
Transient Electromagnetic ◽  
Working Face ◽  
Electromagnetic Detection ◽  
Floor Failure ◽  
Collapse Column

Abstract In order to find out the characteristics of geological isomer exposed in the mining process of 12318 working face in Pansan Mine and grasp its influence law on subsequent coal seams mining, the isomer was firstly determined as the collapse column by means of 3D seismic, transient electromagnetic detection, SYT detection and other methods, and its development characteristics, conductivity and water enrichment were identified.Then FLAC3D numerical simulation software was used to analyze the characteristics of vertical stress and plastic failure zone in different coal seams during mining.Finally, by comparing the ultimate failure depth of floor and the thickness of waterproof layer in the process of each coal seam directly pushing through the collapse column, the risk of water inrush and the prevention are analyzed.The results show that the exposed geological isomer is characterized by weak water-rich collapse column.Under the influence of the mining of the previous coal seam and the activation of the collapse column, the subsequent coal seam is in the low stress area before mining, which increases the floor failure and causes the activation of the collapse column more easily during mining.Coal 5# and 4# can be directly pushed through the collapse column, and coal pillar of sufficient width should be left for coal 1# to prevent the collapse column from activating water inrush.

scholarly journals Study on Law of Overlying Strata Breakage and Migration in Downward Mining of Extremely Close Coal Seams by Physical Similarity Simulation

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Xiaobin Li ◽  
Wenrui He ◽  
Zhuhe Xu
Keyword(s):  
Coal Seam ◽  
Coal Pillar ◽  
Coal Seams ◽  
Monitoring Point ◽  
Rock Stratum ◽  
Working Face ◽  
Roof Fall ◽  
And Migration ◽  
Close Coal Seams ◽  
Overlying Strata

Extremely close coal seam groups are widely distributed in China, and the main mining method is downward mining. In the downward mining process of extremely close coal seam groups, the violent movement of overlying strata will cause the redistribution of surrounding rock stress. It not only produces stress concentration on the pillar but also causes the roof of the lower coal seam to be broken and difficulty in maintaining the mining roadway. In this study, the physical similitude modeling method and field observations were used to study the breakage and migration law of overlying strata in the downward mining of extremely close coal seams. Results show that in the process of mining upper coal seam, the first weighting step of the main roof is 37.5 m and the periodic weighting step is 12.5 m. The occurrence of strata separation is beneficial to the prediction of roof weighting. When the working face advances to 25 m, the rock stratum approximating a parallelogram of height 5 m does not collapse, and the working face is relatively dangerous. When mining the lower coal seam, the overall pressure of the working face is large, but the periodic weighting of the working face is not obvious. The first collapse step of the immediate roof is 15 m. When mining the upper and lower coal seams, the subsidence of the monitoring point increases significantly at 17.5 and 15 m, respectively. The roof collapse of the lower coal seam occurs 2.5 m ahead of that of the upper coal seam. The hydraulic value of the support, roof fall height, and sloughing depth in the entire working face reach the maximum at the coal pillar, and the extreme points at the coal pillar are relatively concentrated. This research provides some guidance for the safe and efficient mining of extremely close coal seams in the future.

scholarly journals Numerical simulation study of mining process of upper and lower walls of normal and reverse faults

2021 ◽  
Vol 2083 (3) ◽  
pp. 032071
Author(s):  
Bian Zhuang
Keyword(s):  
Coal Seam ◽  
Numerical Models ◽  
Hanging Wall ◽  
Coal Pillar ◽  
Normal Fault ◽  
Reverse Fault ◽  
Coal Seams ◽  
Working Face ◽  
Geological Conditions ◽  
Mining Coal

Abstract Mining coal seams near faults are prone to various mine disasters, and different mining sequences have different effects on coal seam disasters. Under this background, the numerical models of normal fault hanging wall, normal faultfoot wall, reverse fault hanging wall and reverse fault footwall under the same geological conditions are established. It is found that the stress concentration of coal pillar is the largest in the mining process of hanging wall of normal fault and footwall of reverse fault, and the possibility of inducing coal pillar rockburst is the largest. Affected by the fault, the coal pillar abutment stress between the working face and the fault shows an upward trend. When mining the coal seam near the fault, various methods such as hydraulic fracturing should be adopted to reduce the coal pillar abutment stress and reduce the risk of mine disasters.

scholarly journals Comprehensive technical support for safe mining in ultra-close coal seams: A case study

2021 ◽  
pp. 014459872110093
Author(s):  
Wei Zhang ◽  
Jiawei Guo ◽  
Kaidi Xie ◽  
Jinming Wang ◽  
Liang Chen ◽  
...  
Keyword(s):  
Coal Seam ◽  
Technical Support ◽  
Surrounding Rock ◽  
Coal Seams ◽  
Deformation Control ◽  
Hard Roof ◽  
Working Face ◽  
Close Coal Seams ◽  
Safe Mining

In order to mine the coal seam under super-thick hard roof, improve the utilization rate of resources and prolong the remaining service life of the mine, a case study of the Gaozhuang Coal Mine in the Zaozhuang Mining Area has been performed in this paper. Based on the specific mining geological conditions of ultra-close coal seams (#3up and #3low coal seams), their joint systematic analysis has been performed, with the focus made in the following three aspects: (i) prevention of rock burst under super-thick hard roof, (ii) deformation control of surrounding rock of roadways in the lower coal seam, and (iii) fire prevention in the goaf of working face. Given the strong bursting tendency observed in upper coal seam and lower coal seam, the technology of preventing rock burst under super-thick hard roof was proposed, which involved setting of narrow section coal pillars to protect roadways and interleaving layout of working faces. The specific supporting scheme of surrounding rock of roadways in the #3low1101 working face was determined, and the grouting reinforcement method of local fractured zones through Marithan was further proposed, to ensure the deformation control of surrounding rock of roadways in lower coal seams. The proposed fire prevention technology envisaged goaf grouting and spraying to plug leaks, which reduced the hazard of spontaneous combustion of residual coals in mined ultra-close coal seams. The technical and economic improvements with a direct economic benefit of 5.55 million yuan were achieved by the application of the proposed comprehensive technical support. The research results obtained provide a theoretical guidance and technical support of safe mining strategies of close coal seams in other mining areas.

Mechanical model for the calculation of stress distribution on fault surface during the underground coal seam mining

2021 ◽  
Vol 144 ◽  
pp. 104765
Author(s):  
Hongwei Wang ◽  
Ruiming Shi ◽  
Jiaqi Song ◽  
Zheng Tian ◽  
Daixin Deng ◽  
...  
Keyword(s):  
Stress Distribution ◽  
Coal Seam ◽  
Mechanical Model ◽  
Fault Surface ◽  
Seam Mining

Reasonable Entry Layout of Lower Seam in Multi-Seam Mining Based on Numerical Simulation

2013 ◽  
Vol 295-298 ◽  
pp. 2980-2984
Author(s):  
Xiang Qian Wang ◽  
Da Fa Yin ◽  
Zhao Ning Gao ◽  
Qi Feng Zhao
Keyword(s):  
Numerical Simulation ◽  
Stress Distribution ◽  
Coal Seam ◽  
Coal Mine ◽  
Abutment Pressure ◽  
Surrounding Rock ◽  
Geological Conditions ◽  
Seam Mining

Based on the geological conditions of 6# coal seam and 8# coal seam in Xieqiao Coal Mine, to determine reasonable entry layout of lower seam in multi-seam mining, alternate internal entry layout, alternate exterior entry layout and overlapping entry layout were put forward and simulated by FLAC3D. Then stress distribution and displacement characteristics of surrounding rock were analyzed in the three ways of entry layout, leading to the conclusion that alternate internal entry layout is a better choice for multi-seam mining, for which makes the entry located in stress reduce zone and reduces the influence of abutment pressure of upper coal seam mining to a certain extent,. And the mining practice of Xieqiao Coal Mine tested the results, which will offer a beneficial reference for entry layout with similar geological conditions in multi-seam mining.

scholarly journals Study on Reservoir Properties and Critical Depth in Deep Coal Seams in Qinshui Basin, China

2019 ◽  
Vol 2019 ◽  
pp. 1-7
Author(s):  
Guiqiang Zheng ◽  
Bin Sun ◽  
Dawei Lv ◽  
Zhejun Pan ◽  
Huiqing Lian
Keyword(s):  
Coal Seam ◽  
Step Change ◽  
Gas Content ◽  
Burial Depth ◽  
Critical Depth ◽  
Coal Seams ◽  
Reservoir Properties ◽  
Qinshui Basin ◽  
Geological Conditions ◽  
Change Characteristics

Coalbed methane (CBM) reservoir properties and relationship of properties with burial depth were studied based on the data derived from 204 deep CBM production wells in Qinshui Basin, China. Through the study, it is found that permeability and porosity decrease with the increase of burial depth and the decreasing trend shows step-change characteristics at a critical burial depth. They also show divisional characteristics at certain burial depth. Gas content, geostress, and geotemperature increase with the increase of burial depth, and the increasing trend shows step-change characteristics and also have divisional characteristics at certain burial depth. Based on the previous study on the reservoir property changes with burial depth, three series of critical depth using different parameters are obtained through simulating the critical depth using the BP neural network method. It is found that the critical depth is different when using different parameters. Combined the previous study with the normalization of three different parameter types, the critical depth in Qinshui Basin was defined as shallow coal seam is lower than 650 m and transition band is 650–1000 m, while deep coal seam is deeper than 1000 m. In deep coal seams, the geological conditions and recovery becomes poor, so it can be defined as unfavorable zones. Therefore, other development means, for example, CO2 injection, need to be used to accelerate the deep coal methane development.

scholarly journals Study on the Rheological Failure Mechanism of Weakly Cemented Soft Rock Roadway during the Mining of Close-Distance Coal Seams: A Case Study

2020 ◽  
Vol 2020 ◽  
pp. 1-20
Author(s):  
Wenkai Ru ◽  
Shanchao Hu ◽  
Jianguo Ning ◽  
Jun Wang ◽  
Qingheng Gu ◽  
...  
Keyword(s):  
Coal Seam ◽  
Failure Mechanism ◽  
Coal Pillar ◽  
Soft Rock ◽  
Western China ◽  
Creep Failure ◽  
Mining Areas ◽  
Geological Conditions ◽  
Residual Coal ◽  
Close Distance

During the mining of the shallow-buried and close-distance multiple coal seam, the rheological failure of the surrounding weakly cemented soft rock of the roadway in the lower coal seam under the concentrated stress is very rare. However, the stress on the roof of the upper coal seam is transmitted down through the residual pillar, resulting in this situation. Taking the Gaojialiang coal mine which is located in the mining areas of western China as the research object, the failure mechanism of the roadway roof under the residual coal pillar in the shallow-buried and close-distance multiple seam is studied in combination with field monitoring and numerical simulation. Furthermore, suggestions on the roadway support under such geological conditions are proposed. The results show that the residual coal pillar in the working face of the lower coal seam gradually collapses during the mining of the shallow-buried and close-distance multiple coal seam. The concentrated stress transferred by the coal pillar increases further, which makes the roof stress of the lower coal seam roadway to increase continuously. In addition, the stress of the roadway roof also increases further due to the rotation of the broken rock above the goaf, and the peek region of stress moves to the nongoaf area. Combining the heavy concentrated stress and weakly cemented property, the shallow-buried surrounding rock shows rheological behavior and failure. Therefore, we must pay more attention on the creep failure of the roadway roof under the action of the residual coal pillar even in the shallow-buried coal seam.

scholarly journals Stability Analysis and Derived Control Measures for Rock Surrounding a Roadway in a Lower Coal Seam under Concentrated Stress of a Coal Pillar

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Zhuoyue Sun ◽  
Yongzheng Wu ◽  
Zhiguo Lu ◽  
Youliang Feng ◽  
Xiaowei Chu ◽  
...  
Keyword(s):  
Coal Seam ◽  
Numerical Simulations ◽  
Principal Stress ◽  
Coal Pillar ◽  
Control Measures ◽  
Stress Difference ◽  
Coal Seams ◽  
The Stability ◽  
Close Distance ◽  
Close Distance Coal Seams

Numerical simulations have often been used in close-distance coal seam studies. However, numerical simulations can contain certain subjective and objective limitations, such as high randomness and excessively simplified models. In this study, close-distance coal seams were mechanically modeled based on the half-plane theory. An analytical solution of the floor stress distribution was derived and visualized using Mathematica software. The principal stress difference was regarded as a stability criterion for the rock surrounding the roadway. Then, the evolution laws of the floor principal stress difference under different factors that influence stability were further examined. Finally, stability control measures for the rock surrounding the roadway in the lower coal seam were proposed. The results indicated the following: (1) The principal stress difference of the floor considers the centerline of the upper coal pillar as a symmetry axis and transmits radially downward. The principal stress difference in the rock surrounding the roadway gradually decreases as the distance from the upper coal pillar increases and can be ranked in the following order: left rib > roof > right rib. (2) The minimum principal stress difference zones are located at the center of the left and right “spirals,” which are obliquely below the edge of the upper coal pillar. This is an ideal position for the lower coal seam roadway. (3) The shallowness of the roadway, a small stress concentration coefficient, high level of coal cohesion, large coal internal friction angle, and appropriate lengthening of the working face of the upper coal seam are conducive to the stability of the lower coal seam roadway. (4) Through bolt (cable) support, borehole pressure relief, and pregrouting measures, the roof-to-floor and rib-to-rib convergence of the 13313 return airway is significantly reduced, and the stability of the rock surrounding the roadway is substantially improved. This research provides a theoretical basis and field experience for stabilizing the lower coal seam roadways in close-distance coal seams.

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