scholarly journals Distribution Characteristics and Formation Mechanism of Surface Crack Induced by Extrathick Near Horizontal Seam Mining: An Example from the Datong Coal Field, China

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Yueguan Yan ◽  
Weitao Yan ◽  
Huayang Dai ◽  
Junting Guo
Keyword(s):  
Main Crack ◽  
Crack Density ◽  
Mining Area ◽  
Outer Edge ◽  
Surface Cracks ◽  
Exposed Area ◽  
Covered Area ◽  
Secondary Cracks ◽  
Seam Mining ◽  
Fracture Distribution

Under the mining condition of extrathick coal seam, the overburden moves violently, the surface is destroyed seriously, and the discontinuous deformation such as cracks is fully developed. Taking Datong mining area as an example, this paper studies and analyzes the development characteristics and generation mechanism of surface cracks in loose layer covered area and bedrock exposed area by means of field measurement and similar model experiment. In the bedrock exposed area, there is no main crack. The width, length, number, and step drop of surface cracks are relatively small. There are many cracks with the same scale and distributed evenly and parallel. However, in the loose covered area, the main cracks are mainly located above the open-off cut and the stoppage line side that is deviated from the working face. There are many secondary cracks around the main crack, with a large crack density and a few cracks in the outer edge of the main crack. Through research, it is found that three mining faces belong to the typical three-zone mining mode and the main fracture is consistent with the O-ring fracture distribution theory. This research’s results can provide theoretical and technical support for the follow-up land remediation and ecological restoration.

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 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 Calculation Method of Overburden Damage Height Based on Fracture Mechanics Analysis of Soft and Hard Rock Layers

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Liang Chen ◽  
Shaowu Fan ◽  
Can Zhao ◽  
Lang Zhang ◽  
Zhiheng Cheng
Keyword(s):  
Fracture Mechanics ◽  
Coal Seam ◽  
Calculation Method ◽  
Hard Rock ◽  
Soft Rock ◽  
Mining Area ◽  
Overburden Rock ◽  
Rock Interaction ◽  
Mechanics Analysis ◽  
Seam Mining

Under the geological condition of soft and hard rock interaction stratum, the overburden damage height can provide a quantitative support for the design of the locations of gas drainage boreholes in the roof mining fracture zone and the determination of the hydraulic fracture zone in coal seam mining. The interbedded structure of overlying mud rock and sandstone in the Lu’an mining area in Shanxi is a typical soft and hard rock interaction stratum. In view of the lack of soft rock fracture mechanics analysis and the improper calculation of the damage height of overburden rock caused by constant rock residual bulking coefficient to be used regularly in the analysis, in this paper, we constructed a fracture model of soft and hard strata by giving a quantitative classification criterion of soft and hard rocks and introducing a fracture failure criterion of soft rock strata and the space constraint condition of broken-expansion rock formation. Aiming at improving the calculation precision of overburden damage height, we presented a calculation method based on fracture mechanics analysis of soft and hard strata, which could delineate the extent of intact rock in overlying strata from bottom to top to determine the damage height of overburden rock. This research took Yuwu coal mine in Lu’an mining area as an example. Results showed that (1) by the calculation method, the overburden damage height of the N1102 fully mechanized caving face in Yuwu coal mine was 51.44 m, which was less than the value obtained by an actual borehole TV method as well as the numerical simulation result of 53.46 m, with a calculation accuracy about 96.22%, which is quite high for both. The calculation accuracy of the proposed method was higher than that of the three conventional theoretical methods, and it effectively solved the limitation of the fracture analysis method without the inclusion of the soft rock layer in design and the distortion problem due to the residual bulking coefficient to be improperly used in simulation. (2) There was no noticeable fractures in the broken soft rock zone, and the whole fractures were mainly low-angle rupture; the fractures in hard rock layer had obvious ruptures and multiangle cracks, and the average fracture width of soft rock was 2.8 mm smaller than that of hard rock. The fracture modes of soft rock and hard rock were mainly tensile failure and tensile shear failure, which verified the correctness of the fracture mechanics model of soft and hard rock layers constructed in this paper. (3) It is noticed that the tensile strength of rock in this method needs to be obtained through rock mechanics experiment on overlying strata in the study area, and our proposed method was applicable to the mining conditions of near horizontal coal seam. The calculation accuracy of this method meets the engineering error requirements and can be applied to the prediction of overburden damage height in near horizontal coal seam mining.

scholarly journals Study on the Law of Surface Cracks While Coal Mining in the Thin Bedrock and Thick Unconsolidated Layer of Yu-Shen-Fu Mining Area

2018 ◽  
Vol 53 ◽  
pp. 03040
Author(s):  
Wu Zuoqi ◽  
Wang Guoku ◽  
Zhao Liqin
Keyword(s):  
Coal Mining ◽  
Ground Surface ◽  
Mining Area ◽  
Dynamic Evolution ◽  
Surface Cracks ◽  
Whole Process ◽  
Thin Bedrock ◽  
The Law ◽  
Mining Face ◽  
Overlying Strata

The law of surface cracks caused by coal mining in ther thin bedrock and thick unconsolidated layer was studied in Yu-Shen-Fu mining area. The crack development in the overlying strata of the coal mining face was detected by drilling survey technology, the whole process of the ground surface crack dynamic evolution was carried out by similar material simulation, and the law of surface cracks evolution was verified by on-site tracking measurement. The study reached the regulation of the overlying strata failure and dynamic evolution of surface cracks caused by coal mining under thin bedrock and thick unconsolidated layer in Yu-Shen-Fu mining area, which can provide theoretical support for the ecological restoration of western mining area.

scholarly journals Research on Surface Failure Law of Working Faces in Large Mining Height and Shallow Buried Coal Seam

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Zhenhua Li ◽  
Yingkun Pang ◽  
Yongsheng Bao ◽  
Zhanyuan Ma
Keyword(s):  
Near Field ◽  
Mining Area ◽  
Surface Cracks ◽  
Large Space ◽  
Key Strata ◽  
Key Stratum ◽  
Surface Failure ◽  
Working Face ◽  
Large Mining Height ◽  
Mining Height

In the process of high-intensity and large-space mining in Shendong mining area, various surface cracks are generated on the surface, resulting in serious damage to the surface buildings and the local ecological environment. To study the influence of overlying rock movement on surface failure of near-field single key strata of near-shallow buried and large mining height working face, the relationship between overburden movement, strata pressure appearance, and surface failure at working face 52307 in Daliuta mining area was analyzed by field measurement and numerical simulation. The results show the following: (1) there is only one thick and hard key stratum in the overburden of large mining height and near-shallow buried working face. Under the condition of presplitting roof blasting, the first weighting step is still as high as 95 m, and the periodic breaking step of roof is 20–30 m. During the weighting, the working resistance of support is still close to the rated resistance. (2) The single key stratum plays an obvious role in controlling overburden movement. After the first weighting of the working face, a stepped subsidence crack appears on the surface within a short time, and the crack lags behind the working face for about 5 m. (3) During each periodic weighting process, the breaking and subsidence of key blocks are accompanied by surface cracks.

Study on Technology of Fully-Mechanized Sub-Level Caving Mining Technology in the Datong Permo Carboniferous Coal Seam

2012 ◽  
Vol 616-618 ◽  
pp. 565-568
Author(s):  
Bin Yu ◽  
Jun Zhao ◽  
Hong Chun Xia
Keyword(s):  
Coal Seam ◽  
Mining Area ◽  
Hard Coal ◽  
Control Technology ◽  
Mining Technology ◽  
Hard Roof ◽  
Sublevel Caving ◽  
Seam Mining ◽  
Longwall Top Coal Caving ◽  
And Control

This thesis briefly introduced roof control technology in fully-mechanized sublevel caving mining with hard roof and hard coal seam, Mining technology , gas prevention and comprehensive prevention and control technology in spontaneous combustion of coal, which in longwall top-coal caving face with hydraulic support in thickness seam in the Datong permo carboniferous coal seam . New development directions of fully-mechanized sublevel caving mining technology in the Datong mining area in the next few years.

scholarly journals Experimental Study on High-Pressure Air Blasting Fracture for Coal and Rock Mass

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Jie Gao ◽  
Haifeng Wang ◽  
Wei Qin ◽  
Qi Ma ◽  
Guanyu Yang
Keyword(s):  
High Pressure ◽  
Main Crack ◽  
Experimental System ◽  
Development Stage ◽  
Gas Pressure ◽  
Fracture Pressure ◽  
Experimental Block ◽  
Jet Impact ◽  
Secondary Cracks ◽  
Gas Volume

In order to research on the issue of high-pressure gas blasting fracture deeply, a high-pressure gas blasting cracking experimental system was established; the effects of gas pressure and gas volume on the morphology of crack growth were studied; the p-t curve of pressure in the blasting process with time was obtained; and the mechanism of high-pressure gas blasting cracking was analyzed in this paper. The conclusion has shown that the stage of effect of high-pressure gas blasting on the test block includes three stages: the gas jet impact stage, the crack initiation and development stage, and the perforation fracture stage. In the design of gas pressure of 5 MPa, the experimental block only produces one longitudinal main crack. As the gas pressure increases to 7.5 MPa and 10 MPa, besides forming one longitudinal main crack, a transverse main crack is formed with further expanded 4–6 secondary cracks. In the same design of gas pressure regardless of volume size, each pressure variation stage has the same length, and the experimental block of the cracking pressure is basically the same. With the higher design pressure, the cracking pressure and the fracture pressure are higher. In the same design of gas pressure, with the larger gas volume, the fracture pressure required for the experimental block is smaller.

scholarly journals The Development Law of Mining-Induced Surface Cracks in Shallow Coal Seam Through Double Gullies Terrain: A Case Study in a Mine

2021 ◽  
Author(s):  
Mingjiao Lu ◽  
Xueyang Sun ◽  
Enke Hou ◽  
Cheng Li ◽  
Yonggang Zhang
Keyword(s):  
Coal Seam ◽  
Relative Position ◽  
Simulation Experiment ◽  
Slope Angle ◽  
Vertical Displacement ◽  
Surface Cracks ◽  
Maximum Width ◽  
Working Face ◽  
Shallow Coal Seam ◽  
Seam Mining

Abstract Mining-induced surface cracks in gullies in shallow seams seriously threaten the development of ecological stability and the safety of mine production. The development law of surface cracks in shallow coal seam mining through double gullies terrain was studied, by taking the Cao Jiatan coal mine in the Yushen Mining Area as a project example. The function T and its discriminant were first put forward to describe the relative position both the surface cracks and working face advanced in shallow coal seam mining through double gullies terrain. The relationship between valley parameters of double gullies terrain and the relative position of surface cracks development was discussed through numerical simulation experiment, similar material simulation experiment and theoretical analysis. The results showed that when the working face passed through the G1 gully, the development of surface cracks led the working face. There were four surface cracks with a maximum width of 23 cm, and the maximum vertical displacement was 11 cm; while passing through the G2 gully, the development of surface cracks lagged the working face. There were seven surface cracks with a maximum width of 79 cm, and the maximum vertical displacement was 45 cm. It can be concluded that the relative position of crack development is greatly affected by geological conditions, gully depth, slope angle, span and other factors of the gully, among of which the gully slope angle is the main influencing factor. T and |T| value has a certain correlation with the lagging distance, crack width, vertical displacement and the total number of cracks in a single gully.

Study on Movement Law of Overlying Strata during Shallow Thinner Seam Mining in Shendong Mining Area

2011 ◽  
Vol 361-363 ◽  
pp. 188-192
Author(s):  
Xi Cheng Zhang ◽  
Zhong Cheng Qin ◽  
Qing Hai Li ◽  
Ning Zhang
Keyword(s):  
Abutment Pressure ◽  
Initial Pressure ◽  
Mining Area ◽  
Shell Morphology ◽  
Coal Face ◽  
Pressure Step ◽  
Powered Support ◽  
Seam Mining ◽  
First Time ◽  
Overlying Strata

Given the particularity and the first time for shallow thinner seam mining in Shendong mining area, the overlying strata movement law during shallow thinner coal seam mining has been studied in this paper based on the fully mechanized thinner coal face of NO.71301 in Shi Getai coal mine, resorting to observation on spot, numerical simulation and other methods. Through research, the important laws and features had been obtained, such as, initial pressure step, periodical pressure step, the obvious partition of periodical weighting, the unitary elasticity distribution of front abutment pressure, and the stress shell morphology over the mining rock, which provides important characteristic for roof control and foundation for the powered support selection.

scholarly journals Analysis of Microwave Thermal Stress Fracture Characteristics and Size Effect of Sandstone under Microwave Heating

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3614
Author(s):  
Feng Gao ◽  
Yan Shao ◽  
Keping Zhou
Keyword(s):  
Thermal Expansion ◽  
Microwave Heating ◽  
Wave Velocity ◽  
Fracture Mode ◽  
Main Crack ◽  
Microwave Energy ◽  
P Wave ◽  
Melt Fracture ◽  
Fracture Characteristics ◽  
Secondary Cracks

Microwave-induced rock fracture is one of the promising approaches of achieving non-blasting continuous mining and assisted mechanical rock breaking. It is of great theoretical and practical significance to study the temperature effect and fracture characteristics of rocks of different sizes under microwave heating; however, there are few studies in this field. Microwave heating of φ 50 × 100 mm, φ 50 × 50 mm, and φ 50 × 25 mm sandstone samples with different heating powers and times was performed to measure the temperature of the sample, the microwave energy absorbed, the mass, and the P-wave velocity before and after heating. The results show suppress that (i) under the same heating conditions, the mass difference and the temperature increase range of φ 50 × 100 mm and φ 50 × 50 mm samples are larger than that of the φ 50 × 25 mm samples; (ii) the wave velocity change rate and the damage factor of samples increase with the increase of heating power and time; (iii) different size specimens have different crack- propagation modes. The main crack of φ 50 × 100 mm specimens usually starts from the middle of the height of the specimen; for the φ 50 × 50 mm specimens, it usually starts from the middle or bottom-end surface of the specimen height; the main crack of φ 50 × 25 mm specimens starts from the vertical surface of the specimen. With an increase in the heating time, the length and width of the main crack continuously increase and secondary cracks are generated. The fracture mode of the sample is also related to the size of the sample. The fracture mode can be divided into three parts: melt fracture, thermal-expansion fracture, and secondary thermal-expansion fracture. The relationship between the sample temperature and the absorbed microwave energy is approximately linear.

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