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

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.

Download Full-text

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

Energy Exploration & Exploitation ◽

10.1177/01445987211009390 ◽

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.

Download Full-text

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

Energy Exploration & Exploitation ◽

10.1177/0144598717747622 ◽

2017 ◽

Vol 36 (5) ◽

pp. 1265-1278 ◽

Cited By ~ 12

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.

Download Full-text

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

10.21203/rs.3.rs-779433/v1 ◽

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.

Download Full-text

Analysis of coal face stability of lower coal seam under repeated mining in close coal seams group

Scientific Reports ◽

10.1038/s41598-021-04410-5 ◽

2022 ◽

Vol 12 (1) ◽

Author(s):

Yu Xiong ◽

Dezhong Kong ◽

Zhijie Wen ◽

Guiyi Wu ◽

Qinzhi Liu

Keyword(s):

Coal Seam ◽

Shear Failure ◽

Coal Seams ◽

Coal Face ◽

Soft Coal ◽

Mechanics Model ◽

Roof Structure ◽

Working Face ◽

Close Coal Seams ◽

Similar Simulation

AbstractAiming at the problem of coal face failure of lower coal seam under the influence of repeated mining in close coal seams, with the working face 17,101 as a background, the coal samples mechanics test clarified the strength characteristics of the coal face under repeated mining, through similar simulation experiments, the development of stable roof structure and surrounding rock cracks under repeated mining of close coal seams are further explored. And based on this, establish a coal face failure mechanics model to comprehensively analyze the influence of multiple roof structural instabilities on the stability of the coal face. Finally, numerical simulation is used to further supplement and verify the completeness and rationality of similar simulation experiment and theoretical analysis results. The results show that: affected by repeated mining disturbances, the cracks in the coal face are relatively developed, the strength of the coal body is reduced, and the coal face is more prone to failure under the same roof pressure; During the mining of coal seam 17#, the roofs of different layers above the stope form two kinds of "arch" structures and one kind of “voussoir beam” structure, and there are three different degrees of frequent roof pressure phenomenon, which is easy to cause coal face failure; Under repeated mining of close coal seams, the roof pressure acting on the coal face is not large. The main controlling factor of coal face failure is the strength of the coal body, and the form of coal face failure is mostly the shear failure of soft coal. The research results can provide a theoretical basis for coal face failure under similar conditions.

Download Full-text

Research on Stability of Overburden Structure around Longwall Mining Face in Steeply Dipping Seam Group

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.724.100 ◽

2015 ◽

Vol 724 ◽

pp. 100-110

Author(s):

Shi Guang Ren ◽

Yong Ping Wu ◽

Jian Hui Yin

Keyword(s):

Coal Seam ◽

Longwall Mining ◽

Coal Pillar ◽

Beam Theory ◽

Coal Seams ◽

Working Face ◽

Rock Structure ◽

Longitudinal Bending ◽

Mining Face ◽

The Stability

The steeply dipping seam group is defined by the two or more coal seams ,a pitch between 35°~55°. Using masonry beam theory, longitudinal bending theory and “R-S-F” dynamics control theory built a lower area overburden structure mode. Analysed the stability of low position coal seam. The balance requirement and the strength of the structure which is affected by the caving rock and lower coal roof were given. It easily generates two lower position steps rock structure in inclination along working face. Regular breaking of the second structure is the main reason leads to the imbalance of the structure between upper coal pillar and upper coal mining face.The interaction among multiple coal seam panels and overburden structures is the main reason that causes the rock disaster, the unbalance of the lower area may lead to pushing accident, the imbalance of the upper area can generate shock pressure.

Download Full-text

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

Journal of Physics Conference Series ◽

10.1088/1742-6596/2083/3/032071 ◽

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.

Download Full-text

Characteristics of Stratum Structure and Fracture Evolution in Stratified Mining of Shallow Buried High-Gas-Thick Coal Seam by Similarity Simulation

Geofluids ◽

10.1155/2021/5555451 ◽

2021 ◽

Vol 2021 ◽

pp. 1-18

Author(s):

Qin Guangpeng ◽

Cao Jing ◽

Wang Chao ◽

Wu Shuo ◽

Zhai Minghua

Keyword(s):

Coal Seam ◽

Coal Mine ◽

Coal Pillar ◽

Structure Evolution ◽

Thick Coal Seam ◽

Fracture Structure ◽

Working Face ◽

Rock Structure ◽

Type Fracture ◽

Overlying Strata

The stratified mining of super thick coal seam is a process of repeated disturbance of the top roof, especially in the lower stratification, the upper complex rock layer has a greater settlement space, resulting in great changes in the strata structure and fissure distribution. The main coal seam thickness of Rujigou Coal Mine exceeds 20 m, due to the high gas content of the coal seam, it is prone to spontaneous combustion, and the stratified mining method is adopted. When a small-size section coal pillar (less than 10 m) is used, the complex rock structure evolution and fissure development characteristics during the stratified mining of shallow buried thick coal seam will directly affect the movement of gas transportation between the working face and the goaf and will directly affect the safety of the working face. Taking Rujigou coal mine as engineering background, this paper analyzes the breaking structure, fracture development, and evolution law of overlying strata in different layers and different sections of coal seam when the buried depth is shallow, and the extra-thick coal seam is stratified mining. The results show that in the process of stratified mining, the overlying strata break, in addition to the whole trapezoidal failure structure, will also form a local F type fracture structure, and with the stratified downward mining, the F type fracture structure will continue to move up and disappear until it is compacted. The “V” type and “U” type subsidence characteristics of different strata overburden are presented after mining in stratified working face of extra-thick coal seam, and the subsidence amount is approximately symmetrical distribution along the middle line of goaf. In the mining process of the lower part of the layer, the end broken rock block is easy to slip along the hinge point by the hinged rock beam structure, and the sliding instability occurs. In the process of stratified mining of ultrathick coal seam, the main fissure of overburden is mainly longitudinal fissure, and it is very easy to form through with the upper layer and will finally connect with the surface under the condition of shallow buried depth. The inclined cracks connected with the adjacent goaf are formed above the coal pillar of the section, which becomes the passage of gas migration in the goaf. The research conclusion shows that for the stratified mining of high gas thick coal seam, special attention should be paid to the treatment of the gas on the stratified working face. In addition to the conventional gas treatment measures such as coal seam prepumping, the buried pipe pumping in the mining area can also be adopted, which can effectively reduce the gas concentration of the working surface.

Download Full-text

Surrounding Rock Movement of Steeply Dipping Coal Seam Using Backfill Mining

Shock and Vibration ◽

10.1155/2021/5574563 ◽

2021 ◽

Vol 2021 ◽

pp. 1-17

Author(s):

Wenyu Lv ◽

Kai Guo ◽

Jianhao Yu ◽

Xufeng Du ◽

Kun Feng

Keyword(s):

Numerical Simulation ◽

Coal Seam ◽

Surrounding Rock ◽

Maximum Deflection ◽

Coal Seams ◽

Physical Similarity ◽

Working Face ◽

Rock Structure ◽

Backfill Mining ◽

The Stability

The movement of the overlying strata in steeply dipping coal seams is complex, and the deformation of roof rock beam is obvious. In general, the backfill mining method can improve the stability of the surrounding rock effectively. In this study, the 645 working face of the tested mine is used as a prototype to establish the mechanical model of the inclined roof beam using the sloping flexible shield support backfilling method in a steeply dipping coal seam, and the deflection equation is derived to obtain the roof damage structure and the maximum deflection position of the roof beam. Finally, numerical simulation and physical similarity simulation experiments are carried out to study the stability of the surrounding rock structure under backfilling mining in steeply dipping coal seams. The results show the following: (1) With the support of the gangue filling body, the inclined roof beam has smaller roof subsidence, and the maximum deflection position moves to the upper part of working face. (2) With the increase of the stope height, the stress and displacement field of the surrounding rock using the backfilling method show an asymmetrical distribution, the movement, deformation, and failure increase slowly, and the increase of the strain is relatively stable. Compared with the caving method, the range and degree of the surrounding rock disturbed by the mining stress are lower. The results of numerical simulation and physical similarity simulation experiment are generally consistent with the theoretically derived results. Overall, this study can provide theoretical basis for the safe and efficient production of steeply dipping coal seams.

Download Full-text

A Mechanical Model of the Overlying Rock Masses in Undersea Coal Mining and a Stress-Seepage Coupling Numerical Simulation

Advances in Civil Engineering ◽

10.1155/2018/8161498 ◽

2018 ◽

Vol 2018 ◽

pp. 1-14 ◽

Cited By ~ 1

Author(s):

Jie Fang ◽

Lei Tian ◽

Yanyan Cai ◽

Zhiguo Cao ◽

Jinhao Wen ◽

...

Keyword(s):

Numerical Simulation ◽

Coal Seam ◽

Coal Mining ◽

Water Inrush ◽

Mining Area ◽

Analysis Model ◽

Fractured Zones ◽

Working Face ◽

Seam Mining ◽

Overlying Strata

The water inrush of a working face is the main hidden danger to the safe mining of underwater coal seams. It is known that the development of water-flowing fractured zones in overlying strata is the basic path which causes water inrushes in working faces. In the engineering background of the underwater mining in the Longkou Mining Area, the analysis model and judgment method of crack propagation were created on the basis of the Mohr–Coulomb criterion. Fish language was used to couple the extension model into the FLAC3d software, in order to simulate the mining process of the underwater coal seam, as well as to analyze the initiation evolutionary characteristics and seepage laws of the fractured zones in the overlying strata during the advancing processes of the working face. The results showed that, during the coal seam mining process, the mining fractured zones which had been caused by the compression-shear and tension-shear were mainly concentrated in the overlying strata of the working face. Also, the open-off cut and mining working face were the key sections of the water inrush in the rock mass. The condition of the water disaster was the formation of a water inrush channel. The possible water inrush channels in underwater coal mining are mainly composed of water-flowing fractured zones which are formed during the excavation processes. The numerical simulation results were validated through the practical engineering of field observations on the height of water-flowing fractured zone, which displayed a favorable adaptability.

Download Full-text

The Key Stratum Structure Morphology of Longwall Mechanized Top Coal Caving Mining in Extra-Thick Coal Seams: A Typical Case Study

Advances in Civil Engineering ◽

10.1155/2020/7916729 ◽

2020 ◽

Vol 2020 ◽

pp. 1-13 ◽

Cited By ~ 1

Author(s):

Fulian He ◽

Xiaobin Li ◽

Wenrui He ◽

Yongqiang Zhao ◽

Zhuhe Xu ◽

...

Keyword(s):

Coal Seam ◽

Cantilever Beam ◽

Coal Seams ◽

Key Strata ◽

Key Stratum ◽

Structure Morphology ◽

Coal Wall ◽

Coal Seam Thickness ◽

Longitudinal Cracks ◽

Overlying Strata

Longwall mechanized top coal caving mining (LMTCCM) in extra-thick coal seams has its own characteristics. The law of mining pressure and overlying strata failure height in extra-thick coal seams are much larger than those of medium-thick and thick coal seams. The key stratum structure morphology also has an important influence on the law of overlying strata movement and stability of surrounding rock. Based on the engineering geological conditions, this paper used the method of theoretical analysis and numerical simulation to study the key stratum structure morphology of LMTCCM in extra-thick coal seams. The results show that under the condition of LMTCCM in extra-thick coal seams, the key stratum forms the structure of low cantilever beam and high hinged rock beam. With the increase of coal seam thickness, the breaking position of cantilever beam is closer to the coal wall. Through theoretical calculation, it is obtained that the breaking length of cantilever beam is 31.5 m and the breaking position of cantilever beam is 15.4 m away from coal wall. With the increase of cycle, key strata will undergo the evolution law from the generation of longitudinal cracks to the hinged structure and then to the cantilever beam structure. The breakage of key strata will cause the expansion of longitudinal cracks and the overall synchronous movement of overlying strata. With the increase of coal seam thickness, the distribution of longitudinal cracks will gradually transfer from the upper part of goaf to the deep part of coal body in space and increase in quantity. This research is of great significance for improving the stability of overlying strata and ensuring the safe and efficient mining of extra-thick coal seams.

Download Full-text