Evolution Characteristics of Composite Pressure-Arch in Thin Bedrock of Overlying Strata During Shallow Coal Mining

2019 ◽  
Vol 11 (03) ◽  
pp. 1950030 ◽  
Author(s):  
S. R. Wang ◽  
X. G. Wu ◽  
Y. H. Zhao ◽  
P. Hagan ◽  
C. Cao
Keyword(s):  
Coal Mining ◽  
Structural Characteristics ◽  
In Situ Stress ◽  
Instability Criterion ◽  
Far Field ◽  
Mining Condition ◽  
Evolution Characteristics ◽  
Mechanical Models ◽  
Movement Rules ◽  
Overlying Strata

Under the shallow coal mining condition and based on the cracking and movement rules of the roof in different mining stages, the mechanical models of symmetrical pressure-arch, stepped pressure-arch, rotating-squeezed pressure-arch in the mining field were established. Then, the instability criterion of each pressure-arch structure was derived. Through the similarity material experiment and numerical simulation, the evolution characteristics of the composite pressure-arches in the near- and far-field were revealed. Results show that the stepped pressure-arch in broken blocks of the basic roof was formed when the horizontal principal stress was greater than the in-situ stress. The broken blocks’ sliding could induce roof cutting off and strong weighting load. The structural characteristics of the overlying strata were determined by the thickness of the bedrock. The upper broken rocks formed a symmetrical pressure-arch in the near- and a far-field pressure-arch formed in the mining field. The median periodic broken rocks formed the rotating-squeezed pressure-arch, bearing the load of the loose layers and protecting the mining panel. After all bedrocks breaking, the latter arch foot of the far-field pressure-arch was transferred to the compacted caving zone. This study can provide a theoretical reference for the similar mining engineering.

Research on Overlying Strata Movement and Deformation under the Conditions of Shortwall and Longwall Mining

2011 ◽  
Vol 90-93 ◽  
pp. 1299-1302 ◽  
Author(s):  
Kuo Li ◽  
Yong Bo Zhang
Keyword(s):  
Coal Mining ◽  
Longwall Mining ◽  
Strata Movement ◽  
Damage Level ◽  
Mining Condition ◽  
Movement And Deformation ◽  
Overlying Strata Movement ◽  
Overlying Strata ◽  
Subsidence Curve

We simulate the rock’s movement and defoemation process in the coal mining, and research the overlying strata movement and deformation under the conditions of shortwall and longwall mining. The conclusion of the experiment indicates: with the method of double deck mining, the rock’s damage level in caving layer is more serious, the final subsidence curve presents a tooth geometry. The subsidence curve of fissure and flexure zone is simily with the longwall mining condition.

Principle of Well-Net Design for Coalbed Methane Exploitation in Coal Mine Area

2014 ◽  
Vol 543-547 ◽  
pp. 3967-3973
Author(s):  
Bao Shan Han
Keyword(s):  
Coal Mining ◽  
Coal Mine ◽  
Coalbed Methane ◽  
Design Theory ◽  
Surface Condition ◽  
Coal Pillar ◽  
Negative Influence ◽  
In Situ Stress ◽  
Well Location

There are abundant CBM (Coalbed Methane) in China. These CBM has caused a remarkable problem to the coal-mining in China. In order to improve the structure of Chinese energy and eliminate the risk of coal mine gas, the relevant industries and sections have implemented many explorations in CBM enriched areas. With great achievements, there are many important problems in the actions of CBM exploitation. The disadvantageous interaction of the surface CBM well and the later coal mining has been ignored at all. There are many disadvantages and defects. To solve these problems and eliminate or weaken the disadvantageous, the scientific and reasonable design of surface CBM well location is an important step. With the thinking of surface condition, coal mining plan, the arrangement of coal mine laneway, the direction and scale of the in-situ stress, and thinking more about the negative influence to and of surface CBM well, according to the theories of mining dynamics, mining engineering, mining geomechanics, and the CBM engineering, the design theory of the surface CBM well net can be studied. Finally, the arrangement principle of CBM product well in coal field is presented. The existing or future coal pillar will be a critical location for the surface CBM well location.

scholarly journals Study on Fracture and Stress Evolution Characteristics of Ultra-Thick Hard Sandstone Roof in the Fully Mechanized Mining Face with Large Mining Height: A Case Study of Xiaojihan Coal Mine in Western China

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Feng Ju ◽  
Meng Xiao ◽  
Zequan He ◽  
Pai Ning ◽  
Peng Huang
Keyword(s):  
High Strength ◽  
Western China ◽  
Stress Evolution ◽  
Working Face ◽  
Mining Condition ◽  
Evolution Characteristics ◽  
Large Mining Height ◽  
Evolution Laws ◽  
Mining Face ◽  
Mining Height

Ultra-thick hard sandstone roofs present high thickness, poor delamination, and wide caving range. The strata pressure of the working face during actual mining increases, having a significant influence on the safe mining of the working face. Especially, in the mining areas of western China, the fully mechanized mining faces with high mining height and high-strength mining are more prominent. Understanding the fractures and stress evolution characteristics of the ultra-thick hard sandstone roof during actual mining is of high significance to control the dynamic pressure on the working face. In this paper, the typical ultra-thick hard sandstone roof of the Xiaojihan coal mine was taken as an example. The structural and chemical composition characteristics were analyzed. Besides, the fracture characteristics of ultra-thick hard roof during the working face mining were analyzed. Moreover, the fracture structure consistency was verified through physical simulation and a field measurement method. Finally, the stress evolution laws in the ultra-thick hard sandstone roof fracture were studied through numerical simulation. The findings demonstrated that (1) the ultra-thick hard sandstone roof was composed of inlaid coarse minerals, which had compact structure, while the Protodyakonov hardness reached up to 3.07; (2) under the high-strength mining condition of fully mechanized mining face with large mining height, the ultra-thick hard sandstone roof had the characteristics of brittle fracture, with a caving span of 12 m; (3) under the high-strength mining condition of fully mechanized mining face with large mining height, the ultra-thick hard sandstone roof followed the stress evolution laws that were more sensitive to the neighboring goaf. Therefore, it was necessary to reduce the fracture span or layering of ultra-thick hard sandstone roof through the manual intervention method adoption or increase either the strength of coal pillar or supporting body, to resist the impact generated during ultra-thick hard sandstone roof fracture.

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 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.

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

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
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.

scholarly journals Research on the Disaster-Inducing Mechanism of Coal-Gas Outburst

2020 ◽  
Vol 2020 ◽  
pp. 1-12 ◽  
Author(s):  
Fengxiang Nie ◽  
Honglei Wang ◽  
Liming Qiu
Keyword(s):  
Coal Mining ◽  
In Situ Stress ◽  
Gas Pressure ◽  
Underground Coal Mining ◽  
Coal Gas ◽  
Gas Outburst ◽  
Mining Depth ◽  
Mining Coal ◽  
Occurrence Mechanism

In China, coal-gas outburst is seriously affecting safety of the coal mine. To improve the safety status of underground coal mining, this work investigated the evolution process and occurrence mechanism of coal-gas outburst under the coupling action of stress and gas. Results show that increasing either gas pressure or in-situ stress can make coal destroy and destabilize, and the contribution of gas pressure to coal failure is twice that of in-situ stress. In ultradeep coal mining, coal-gas outburst may occur even under the condition of low gas pressure due to large in-situ stress. Moreover, the larger the mining depth is, the lower the gas index is required for disaster occurrence. The results have certain guiding significance for coal energy mining and the control of coal-gas outburst in deep coal mining.

scholarly journals Surface Subsidence Prediction Method for Coal Mines with Ultrathick and Hard Stratum

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Hongkai Han ◽  
Jialin Xu ◽  
Xiaozhen Wang ◽  
Jianlin Xie ◽  
Yantuan Xing
Keyword(s):  
Coal Mining ◽  
Coal Mine ◽  
Prediction Method ◽  
Prediction Equation ◽  
Arbitrary Cross Section ◽  
Surface Subsidence ◽  
Strong Impact ◽  
Subsidence Prediction ◽  
Movement Characteristics ◽  
Mining Condition

Overburden conditions consisting of ultrathick and hard stratum (UTHS) are widespread in China and other countries, but existing surface subsidence prediction methods ignore the strong impact of UTHS on surface subsidence. They are thus not applicable for surface subsidence prediction for coal mining with the presence of UTHS. We conducted actual measurements of surface and UTHS subsidence in the Tingnan Coal Mine. The results showed that under the UTHS mining condition, the required gob dimension is much larger than the empirical value when the surface reaches sufficient mining and that the actual measured maximum value of surface subsidence is much smaller than the empirical value. The UTHS subsidence is approximately equal to the surface subsidence. The movement of UTHS has a strong impact on surface subsidence and has a controlling function for it. It was proposed that surface subsidence could be approximately predicted by calculating the UTHS subsidence. The UTHS movement characteristics were studied using Winkler’s theory of beams on an elastic foundation, the subsidence prediction equation of the main sections in the strike and dip directions was obtained under different mining dimensions, and the subsidence prediction equation of any arbitrary cross section parallel to the two main sections was established. Then, the surface subsidence prediction method for coal mining with the presence of UTHS was developed, and the influences of UTHS thickness, strength, and layer position on the surface subsidence were discussed. The Tingnan Coal Mine was taken as an example, and the subsidence curves of the strike and dip main sections were calculated using different mining dimensions. Subsequently, the surface subsidence after the mining of working faces 204, 205, 206, and 207, respectively, was predicted, and the prediction method was verified by comparing the results with the measured surface subsidence results of working faces 204, 205, and 206.

scholarly journals New Method to Design Coal Pillar for Lateral Roof Roadway Based on Mining-Induced Stress: A Case Study

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Feng Wang ◽  
Shaojie Chen ◽  
Jialin Xu ◽  
Mengzi Ren
Keyword(s):  
Stress Distribution ◽  
Coal Pillar ◽  
In Situ Stress ◽  
New Method ◽  
Maximum Deformation ◽  
Induced Stress ◽  
Stress Contour ◽  
Longwall Panel ◽  
Overlying Strata

The traditional method to design coal pillar for lateral roof roadway was established based on the mining-induced strata movement contour which is considered as a straight line, while ignoring the variations of the internal strata deformation law as well as stress distribution characteristics. In order to make up for this deficiency, in this study, evolution of mining-induced stress in the overlying strata was simulated using physical and numerical simulations, and a method to design coal pillar for lateral roof roadway based on mining-induced stress was proposed. The results indicate that the stress of the overlying strata is redistributed during excavation, and the stress distribution can be divided into a stress-relaxation area, a stress-concentration area, and an in situ stress area. The contour line of 1.05 times the in situ stress is used to define the mining-induced stress contour. Stress inside the contour is redistributed while outside the contour the overlying strata are still within the in situ stress area. Mining-induced stress contour presents a concave-upward type from coal seam to the overlying strata that cannot be merged into a straight one due to their different characteristics of movement and deformation. With this in mind, this study proposed a method to design the width of coal pillar for lateral roof roadway according to the mining-induced stress contour. According to mining-induced stress contour, the width of coal pillar for lateral roof roadway of longwall panel 31100 is 160 m, and the maximum deformation of the roadway is 270 mm. The new method can definitely meet engineering demands.

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