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

2020 ◽  
Vol 2020 ◽  
pp. 1-13 ◽  
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.

scholarly journals The Study of Key Stratum Location and Characteristics on the Mining of Extremely Thick Coal Seam under Goaf

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Gaochuan Guo ◽  
Yongkang Yang
Keyword(s):  
Coal Seam ◽  
Longwall Mining ◽  
Maximum Principal Stress ◽  
Engineering Practice ◽  
Coal Seams ◽  
Thick Coal Seam ◽  
Key Strata ◽  
Key Stratum ◽  
Arch Structure ◽  
Overlying Strata

The basis of traditional ground pressure and strata control techniques is the key strata theory, wherein the position of the key stratum can easily be determined for coal seams with regular thickness and without goaf. However, in the case of mining ultrathick coal seams underneath goaf, the traditional methods used for the calculation of key stratum position need to be improved in order to account for the additional coal seam thickness and the presence of an upper goaf. This study analyzed the failure height and collapse characteristics of overlying strata during excavation for determining the structure of the failed overlying strata. The results indicate that the intercalation and overlying strata gradually evolve into a large “arch structure” and a small “arch structure” during longwall mining, respectively. A mechanical model of the bearing characteristics of the interlayer key strata structure was established according to the structure of the intercalation rock layer, which is a hinged block structure. The results of the model indicate that the maximum principal stress occurs when the key strata portion of the arch structure bears the overlying load. Consequently, the movement and position of the interlayer key strata can be evaluated throughout the mining process of the ultrathick coal seams underneath goaf. This method was used to determine the position of interlayer key stratum of overlying strata in Xiegou coal mine. And the results agree with that of the engineering practice. The results are significant to determine the key strata position during ultrathick coal seam underneath goaf longwall mining.

scholarly journals Movement Laws of Overlying Strata above a Fully Mechanized Coal Mining Face Backfilled with Gangue: A Case Study in Jiulishan Coal Mine in Henan Province, China

2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Zhengkai Yang ◽  
Zhiheng Cheng ◽  
Zhenhua Li ◽  
Chunyuan Li ◽  
Lei Wang ◽  
...  
Keyword(s):  
Coal Mining ◽  
Main Roof ◽  
Surrounding Rock ◽  
Surface Subsidence ◽  
Key Strata ◽  
Key Stratum ◽  
Mining Face ◽  
Failure Depth ◽  
Gangue Backfilling ◽  
Overlying Strata

The aim of this study is to obtain movement laws of overlying strata above a fully mechanized coal mining face backfilled with gangue and solve the problem of surface subsidence during coal mining. This study was carried out based on gangue backfilling mining of Jiulishan Coal Mine (Jiaozuo City, Henan Province, China) from the perspectives of deformation of backfilled gangue under compaction, surrounding rock of a stope, and activities of key strata. The method combining with rock mechanics, viscoelastic mechanics, control theory of rock mass under mining, and numerical simulation was used based on physical and mechanical characteristics of backfilled gangue. On this basis, the research analyzed the temporal-spatial relationships of activities of surrounding rock of the stope, compressive deformation of backfilling body, failure depth of the floor, deformation characteristics of the main roof with laws of surface subsidence. The movement characteristics of overlying strata above the fully mechanized coal mining face backfilled with gangue and the traditional fully mechanized mining face were compared. It is found that, under the same conditions of overlying strata, movement laws of overlying strata are mainly determined by the mining height of coal seams and the heights of a caving zone and a fracture zone are nearly linearly correlated with the mining height. Through analysis based on thin-plate theory and key stratum theory, the location of the main roof of the fully mechanized coal mining face backfilled with gangue in coal seams first bending and sinking due to load of overlying strata was ascertained. Then, it was determined that there are two key strata and the main roof belongs to the inferior key stratum. By using the established mechanical model for the main roof of the fully mechanized coal mining face backfilled with gangue and the calculation formula for the maximum deflection of the main roof, this research presented the conditions for breaking of the main roof. In addition, based on the theoretical analysis, it is concluded that the main roof of the fully mechanized coal mining face backfilled with gangue does not break, but bends. The numerical simulation results demonstrate that, with the continuous increase of strength of backfilled gangue, the stress concentration degree of surrounding rock reduces constantly, so does its decrease amplitude. Moreover, the compressive deformation of backfilling, failure depth of the floor, and bending and subsidence of the main roof continuously decrease and tend to be stable. The mechanical properties of backfilling materials determine effects of gangue backfilling in controlling surface subsidence. Gangue backfilling can effectively control movement of overlying strata and surface subsidence tends to be stable with the increase of elastic modulus of gangue.

scholarly journals Fracture Mechanism in Overlying Strata during Longwall Mining

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Zhengyi Ti ◽  
Jiazhen Li ◽  
Meng Wang ◽  
Kang Wang ◽  
Zhupeng Jin ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Fracture Mechanism ◽  
Longwall Mining ◽  
Flexural Rigidity ◽  
Central Area ◽  
Short Side ◽  
Wall Area ◽  
Key Stratum ◽  
Coal Wall ◽  
Overlying Strata

We used the key stratum theory to establish a more realistic thin-plate mechanical model of elastic foundation clamped boundary and study the fracture mechanism of overlying strata during longwall mining. We analyzed the fracture characteristics and factors affecting fracture of the key stratum combined with the Mohr–Coulomb yield criterion. Besides, we used numerical simulation methods to verify the evolution pattern of the overlying strata fracture. The results show that the fracture mechanisms of the elastic foundation clamped structure’s key stratum varied depending on the position under longwall mining. The advanced coal wall area of the upper surface is a compressive-shear fracture. The center area of the lower surface is a tensile fracture. With the increase of the excavation length and the load of the key stratum, the central area and the advanced coal wall area of the long side are fractured before the advanced coal wall area of the short side. With the increase of flexural rigidity of the key stratum, the advanced coal wall area of the long side fractures before the central area and the advanced coal wall area of the short side. With the increase of the foundation modulus and the advanced load of the key stratum, the central area fractures before the surrounding advanced coal wall area. The advanced influence distance was positively correlated with the key stratum’s flexural rigidity and advanced load and negatively correlated with the foundation modulus and excavation length. The advanced influence distance was not affected by the load of the key stratum. The numerical simulation results show that, with the increase of the mining area, the fracture trace of overlying strata in goaf extended to the coal wall’s interior. The fracture range of overlying strata is larger than that of the miningd: area. This study has a practical value for water disasters, gas outbursts, and rock strata control.

scholarly journals Height of the Fractured Zone in Coal Mining under Extra-Thick Coal Seam Geological Conditions

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Dequan Sun ◽  
Xiaoyan Li ◽  
Zhijie Zhu ◽  
Yang Li ◽  
Fang Cui
Keyword(s):  
Coal Seam ◽  
Coal Mining ◽  
Process Analysis ◽  
Failure Process ◽  
Analysis Method ◽  
Coal Seams ◽  
Fractured Zone ◽  
Seam Mining ◽  
Borehole Televiewer ◽  
Overlying Strata

The height of the fractured zone caused by coal mining is extremely significant for safely mining under water, water conservation, and gas treatment. At present, the common prediction methods of overburden fractured zone height are only applicable to thin and medium-thick coal seams, not suitable for thick and extra-thick coal seams. In order to determine the overburden fractured zone distribution characteristics of extra-thick seam mining, failure process analysis method of overlying strata was proposed based on key strata theory. This method was applied to 15 m coal seam of Tongxin coal mine, and fractured zone height was determined to be 174 m for 8100 panel. EH4 electromagnetic image system and borehole televiewer survey were also conducted to verify the theory results. The distribution of the electrical conductivity showed that the failure height was 150–170 m. Observation through the borehole televiewer showed that the fractured zone height was 171 m. The results of the two field test methods showed that the fractured zone height was 150–171 m, and it was consistent with the theory calculation results. Therefore, this failure process analysis method of overlying strata can be safely used for other coal mines.

The Research on Abutment Stress Distribution and Fracture Characteristics of Coal Seam in Longwall Face

2011 ◽  
Vol 361-363 ◽  
pp. 103-107
Author(s):  
Chuan Ming Li
Keyword(s):  
Stress Distribution ◽  
Coal Seam ◽  
Surrounding Rock ◽  
Geometrical Shape ◽  
Horizontal Distance ◽  
Site Testing ◽  
Fracture Characteristics ◽  
Working Face ◽  
Coal Wall ◽  
Overlying Strata

The abutment stress results from the load coming from overlying strata above the influence range of abutment stress and the load which coming from overlying strata above the stress shell passed by the shell. Through the mechanical calculation,this paper analyzed abutment stress distribution and fracture characteristics of coal seam resulted from the load of overlying strata passed by stress shell which exists in surrounding rock of working face, and obtained the laws of abutment stress distribution and fracture in coal seam in combination with numerical simulation and site testing. The characteristics of abutment stress distribution and fracture are related to the geometrical shape of the stress shell, such as height of the stress shell, horizontal distance between top of stress shell and coal wall,and width of stress shell skewback.

scholarly journals Influence of Upper Seam Extraction on Abutment Pressure Distribution during Lower Seam Extraction in Deep Mining

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Feng Wang ◽  
Zeqi Jie ◽  
Bo Ma ◽  
Weihao Zhu ◽  
Tong Chen
Keyword(s):  
Coal Seam ◽  
Pressure Distribution ◽  
Abutment Pressure ◽  
Field Measurements ◽  
Pressure Relief ◽  
Deep Mining ◽  
Key Strata ◽  
Mining Safety ◽  
Seam Mining ◽  
Overlying Strata

Pressure-relief coal mining provides an effective way to decrease stress concentration in deep mining and ensures mining safety. However, there is currently a lack of research and field verification on the pressure-relief efficiency and influencing factors during upper seam extraction on the lower seam. In order to make up for this deficiency, in this study, field measurements were conducted in panel Y485, which has a maximum depth of 1030 m and is partially under the goaf of the upper 5# seam in the Tangshan coal mine, China, and evolution of advanced abutment pressure was analyzed. Numerical simulations were conducted to study of influence of key strata on advanced abutment pressure. Influence mechanisms of the upper seam extraction on the advanced abutment pressure distribution during lower seam extraction were revealed. The results indicate that the distribution of advanced abutment stress is influenced by the key strata in the overlying strata. The key strata above the upper coal seam were fractured due to the upper coal seam mining, and the advanced abutment stress was only influenced by the key strata between the two seams during lower coal seam mining. When key strata were present between two seams, the extraction of the lower seam still faces potential dynamic disasters after the extraction of the upper seam. In this case, it would be necessary to fracture the key strata between the two seams in advance for the purpose of mining safety. Key strata in the overlying strata of the 5# seam were fractured during extraction, and advanced abutment pressure was only influenced by the key strata located between the two mined seams. The influence distance of advanced abutment pressure in panel Y485 decreased from 73 m to 38 m, and the distance between the peak advanced abutment pressure and the panel decreased from 29 m to 20.5 m, achieving a pronounced pressure-relief effect.

scholarly journals Influence of Valleys Terrain on Pressure of Fully Mechanized Working Faces in Shallow Coal Seams

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
YingJie Liu ◽  
Qingjie Qi ◽  
Anhu Wang
Keyword(s):  
Coal Seam ◽  
Coal Mining ◽  
Rock Fracture ◽  
Mine Pressure ◽  
Overburden Rock ◽  
Coal Seams ◽  
Valley Bottom ◽  
Key Stratum ◽  
Seam Mining ◽  
The Impact

The absence of a key stratum during overburden rock movement is crucial to the mining pressure of fully mechanized coal mining faces. Using physical and numerical simulations, the 21304 mechanized mining in Daliuta and Huojitu coal mining faces 1−2 appeared twice during a pressure frame accident analysis. The results indicate that a lack of key overlying strata is crucial to the mining of lower coal seams, particularly for the upper sections of a single key stratum of coal. When the key stratum of the upper coal seam is absent, a stable masonry structure is formed after mining. It is easy to form stable stacked strata at the bottom of a coal seam. When developing gullies in deep terrains, the formation of the key stratum will be an upper rock fracture affected by the impact, resulting in a partial absence of the key stratum. When the key stratum is absent, the mining of upslope working faces and the probability of dynamic strata pressure increase with the overburden on the working face and mining of downslope faces. The face mine pressure development laws on the upper and lower coal seam mining were similar, mainly manifesting as “slope section >valley bottom section >back slope section.”

scholarly journals Roof structure of shallow coal seam group mining in Western China

PLoS ONE ◽  
2021 ◽  
Vol 16 (8) ◽  
pp. e0255047
Author(s):  
Jian Cao ◽  
Qingxiang Huang
Keyword(s):  
Coal Seam ◽  
Western China ◽  
Beam Structure ◽  
Key Strata ◽  
Key Stratum ◽  
Roof Structure ◽  
Support Resistance ◽  
Shallow Coal Seam ◽  
Mining Height

In order to realize roof control of shallow coal seam group mining in Western China, combining with engineering statistics, physical simulation and theoretical analysis, the roof weighting characteristics during lower coal seam mining were revealed, and the classification of shallow coal seam group was proposed. Based on this, mechanical models of roof structure were set up, and the calculation method of support resistance was determined. The results show that the roof weighting is closely related to the interburden thickness and the mining height of lower coal seam, considering the ratio of interburden thickness to the mining height, as well as the key stratum structure, the classification of shallow coal seam group was put forward. The first type is shallow coal seam group with no key stratum (SCSG-No), its roof pressure is mainly affected by caving roof of upper coal seam, and the interburden roof forms slanting pillar-beam structure. The second type is shallow coal seam group with single key stratum (SCSG-S), interburden roof represents step voussoir beam structure. The third type is shallow coal seam group with double key strata (SCSG-D), interburden roof can form double key strata structure, the lower key stratum forms slanting step voussoir beam structure, while the upper key stratum forms voussoir beam structure, besides, longwall face represents large—small periodic weighting. Through establishing the roof structure models, the calculation formulas of support resistance were determined, it can provide basis for roof control and promote safe mining in Western China.

scholarly journals Overlying strata movement with ground penetrating radar detection in close-multiple coal seams mining

2019 ◽  
Vol 15 (8) ◽  
pp. 155014771986985 ◽  
Author(s):  
Yang Li ◽  
Jiachen Wang ◽  
Yiding Chen ◽  
Zhipeng Wang ◽  
Jianpeng Wang
Keyword(s):  
Coal Seam ◽  
Ground Penetrating Radar ◽  
Longwall Mining ◽  
The United States ◽  
Coal Seams ◽  
Strata Movement ◽  
Longwall Panel ◽  
Ground Penetrating ◽  
Overlying Strata Movement ◽  
Overlying Strata

Longwall mining is a productive mining method that has been widely used in China, the United States, Australia, and Europe. However, due to the subsidence caused by coal mining activities, the phenomenon is complex, longwall mining brings the overburden movement issues accompany with the coal recovery. In subsidence trough, the resulting strata and surface ground movements are regarded as largely contemporaneous with mining, producing more or less direct effects of natural ecology. Ground penetrating radar has been widely used in geological hazard detection due to its high precision, but it is rarely employed in underground measuring the overlying strata movement above the longwall panel. In this article, there are five close-multiple coal seams (5#, 7#, 8#, 9#, 12# seams) within 70 m distance to be monitored in Qian Jiaying coal mine of Kailuan Coal Company in Hebei province. The 7#, 8#, 9#, 12# coal seams were already excavated in sequence. So the 5# coal seam is overmining above the gobs of four coal seams at the top. The ZTR12-series ground penetrating radar equipment is used to detect the development of fractures under the floor of the 5# coal seam. The ZTR12-series ground penetrating radar system has the capability of large depth detection and explosion proof to adapt to the working environment of underground coal mines and can realize fine detection and accurate identification. The maximum detection distance of reflection method can reach 50 m. The measurement results show that the 5# coal seam is in the fracture zone above the gobs of four coal seams, and the caved zone of lower coal seam develops to fine sandstone of the 5# coal seam floor. The ground penetrating radar has shown much promise in the detection of overlying strata movement.

scholarly journals COMPARATIVE ANALYSES OF GEOPHYSICAL LOGS OF RESISTIVITY AS APPLIED TO COAL DEPOSITS

2018 ◽  
Vol 36 (1) ◽  
pp. 19
Author(s):  
Oluwafemi Shekoni Ayodeji ◽  
Paulo Salvadoretti ◽  
João Felipe Coimbra Leite Da Costa ◽  
George Olufunmilayo Gasper ◽  
Douglas Sander Libardi
Keyword(s):  
Coal Seam ◽  
Single Point ◽  
Rio Grande ◽  
Vertical Resolution ◽  
Rio Grande Do Sul ◽  
Coal Seams ◽  
Core Samples ◽  
Coal Deposits ◽  
Geophysical Logs ◽  
Coal Seam Thickness

ABSTRACT. This study compares data sets obtained from three geophysical probes used for measuring rock resistivity. A detailed analysis was carried out to determine which of these probes provides the best option in terms of identification of coal-seam thickness. The resistivity probes used were guard log (GL), single-point resistance (SPR), and induction log (IND) probes. To aid the comparison among the different logs, two other geophysical logs were included: natural gamma (NG) and optical televiewer (OPTV), which helped to identify the coal seams. In the specific case of OPTV, when the situation is favorable, it identifies the coal seams and checks the vertical resolution of the other logs due to its excellent vertical resolution. In this study, analyzed data were obtained from four different coal deposits, namely B3, Calombo, Cerro, and Seival. All the coal deposits mentioned are located in the state of Rio Grande do Sul, Brazil. In all, 13 boreholes with recovered core samples are presented and discussed. The geological descriptions of the 13 boreholes are the main information used as a control parameter in comparisons with the geophysical logs, while OPTV images served as an alternative to verify the vertical resolution of the logs. At the end of the analysis, it was found that the guard log probe tends to offer better performance in the aspect of lithological identification, demonstrating a greater capacity in comparison with the others in terms of vertical resolution. Statistically, it presented the closest estimated value of coal-seam thickness in relation to that provided by geological description of the recovered core samples. Keywords: geophysics, coal, resistivity, OPTV. RESUMO. Este estudo compara registros de perfilagem geofísica obtidos por três sondas que medem a resistividade de litologias. Uma análise detalhada foi feita para determinar qual destas sondas proporciona a melhor opção em termos da identificação de espessuras de camadas de carvão. As sondas de resistividade utilizadas foram: guard log , single point resistance e induction log. Para auxiliar na comparação entre as diferentes sondas, outros dois registros geofísicos foram incluídos: radiação gama natural e optical televiewer (OPTV), os quais ajudaram a identificar os estratos de carvão. No caso específico do OPTV, quando a situação é favorável, ele permite identificar os estratos de carvão e verificar a resolução vertical dos demais registros, em função da excelente resolução vertical. Neste estudo, foram analisados dados obtidos em 4 depósitos de carvão diferentes: B3, Calombo, Cerro e Seival. Todos os depósitos de carvão mencionados situam-se no estado do Rio Grande do Sul – Brasil. Ao todo, 13 furos de sondagem com recuperação de testemunhos são apresentados e discutidos. As descrições geológicas dos 13 furos de sondagem são as informações principais utilizadas como parâmetro de controle nas comparações entre os perfis geofísicos, enquanto que as imagens OPTV serviram como uma alternativa para verificar a resolução vertical dos perfis geofísicos. Ao final das análises, verificou-se que o dispositivo guard log tende a ter o melhor desempenho no aspecto de identificação litológica, demonstrando uma capacidade superior em relação aos demais arranjos em termos de resolução vertical. Estatisticamente, ele apresentou as estimativas de espessurasmais próximas em valor, em relação às espessuras proporcionadas pelas descrições geológicas de testemunhos de sondagem.Palavras-chave: geofísica, carvão, resistividade, OPTV.

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