scholarly journals Evolution Law of Floor Fracture Zone above a Confined Aquifer Using Backfill Replacement Mining Technology

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Shan Ning ◽  
Weibing Zhu ◽  
Xiaoyong Yi ◽  
Laolao Wang
Keyword(s):  
Water Inrush ◽  
Measurement Techniques ◽  
Force Model ◽  
Strip Mining ◽  
Confined Aquifer ◽  
Floor Rock ◽  
Study Results ◽  
Mining Face ◽  
Coal Pillars ◽  
Failure Depth

Disturbances owing to coal mining result in the movement and failure of floor strata. Mining-induced fractures within the floor may propagate to the confined aquifer, thereby causing water inrush disasters. In this study, we propose using strip mining and backfill replacement mining above the confined aquifer to investigate the failure depth of the floor. The problem is simplified as a distributed force model on a half-plane body. First, the stress disturbance of the floor during strip mining is calculated and the results are combined with the von Mises yield criterion. Then, the destruction of the floor after replacing the remaining coal pillars is explored. The results show that the widths of the strip mining face and coal pillars play an important role in affecting the failure depth of the floor: the greater the width, the larger the failure depth. Based on the parametric study results, the mining face and retention coal pillar width of 20 m is sufficient to prevent the occurrence of water inrush accidents. After the replacement of the remaining coal pillars, the failure area of the floor rock mass increases, but the maximum failure depth remains unchanged. Finally, we employed field measurement techniques at the Bucun coal mine to monitor the shear and vertical strains of the floor. The data collected was compared with the predicted results obtained from the proposed theoretical model. Good agreement was found between the monitoring and calculation results, which demonstrate the effectiveness of the proposed method.

scholarly journals Failure Characteristics and Confined Permeability of an Inclined Coal Seam Floor in Fluid-Solid Coupling

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Jian Sun ◽  
Lianguo Wang ◽  
Guangming Zhao
Keyword(s):  
Stress Concentration ◽  
Coal Seam ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Water Inrush ◽  
Equivalent Stress ◽  
Confined Aquifer ◽  
Confined Water ◽  
Floor Water Inrush ◽  
Failure Depth

Secondary development of FLAC3D software was carried out based on FISH language, and a 3D fluid-solid coupling numerical calculation model was established for an inclined seam mining above a confined aquifer in Taoyuan Coal Mine. A simulation study was implemented on the mining failure depth of an inclined coal seam floor, conducting height of confined water, and the position of workface floor with easy water inrush during advancement of workface. Results indicated that, during the advancement of the inclined coal seam’s workface, obvious equivalent stress concentration areas existed in the floor strata, and the largest equivalent stress concentration area was located at the low region of workface floor. When the inclined coal seam workface advanced to about 80 m, the depth of floor plastic failure zone reached the maximum at approximately 15.0 m, and the maximum failure depth was located at the low region of the workface floor. Before the inclined workface mining, original confined water conducting existed on the top interface of the confined aquifer. The conducting height of the confined water reached the maximum at about 11.0 m when the workface was pushed forward from an open-off cut at about 80 m. Owing to the barrier effect of the “soft-hard-soft” compound water-resistant strata of the workface floor, pore water pressure and its seepage velocity in the floor strata were unchanged after the workface advanced to about 80 m. After the strata parameters at the workface floor were changed, pore water pressure of the confined water could pass through the lower region of the inclined workface floor strata and break through the barrier of the “soft-hard-soft” compound water-resistant strata of the workface floor and into the mining workface, resulting in the inclined coal seam floor water inrush. Results of this study can provide a basis for predicting, preventing, and governing the inclined coal seam floor water inrush above confined aquifer.

Study on Broken Floor Rock Mass by Mining Underground Pressure

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Ming Sun ◽  
Chen Guo ◽  
Wenxiang Zheng ◽  
Huiqiang Duan
Keyword(s):  
Rock Mass ◽  
Water Inrush ◽  
Theoretical Formula ◽  
Practical Situation ◽  
Floor Rock ◽  
Limit Value ◽  
Stress Contour ◽  
Mining Disturbance ◽  
Mining Face ◽  
Chinese Coal

As the dangerous level of floor water inrush in Chinese coal field is becoming more and more serious annually, the widely used formulas of broken floor rock mass are belonged to nonlinear type or empirical type. However, they are not well conformed to the practical situation and including mining underground pressure. The biggest depth of broken floor rock mass and the length of gob-floor or mining-floor until the maximum broken floor location are expressed by theoretical formulas on integrity theory. Taking a mining face in Chinese Anhui Province as the object, the relationship between broken floor rock mass and mining underground pressure is studied by numerical simulation, the theoretical analysis, and the DC exploration. The peak and scope of broken floor rock mass will enlarge until reaching limit value with the increasingly advanced distance. The mining gob stress contour is saddle-shaped, and its growing speed is becoming slower, so the 180 m coal mining face has reached the sufficient mining stage. Wave velocity of broken floor rock mass from 0 m to 16 m is greatly decreased by the mining disturbance, and it is basically conformed to theoretical formula and practical situation. The results can be relatively better used in the pressure mining of the Ordovician limestone, because it can provide some safe guarantee for mining deep coal seam.

Microseismic Monitoring and Numerical Simulation Research of Floor Failure Depth in Extra-Thick Coal Seam

2014 ◽  
Vol 881-883 ◽  
pp. 1799-1804 ◽  
Author(s):  
Ai Ping Cheng ◽  
Yong Tao Gao ◽  
Chao Liu ◽  
Jin Fei Chai
Keyword(s):  
Numerical Analysis ◽  
Coal Mining ◽  
Microseismic Monitoring ◽  
Floor Rock ◽  
Thick Coal Seam ◽  
Floor Failure ◽  
Mining Disturbance ◽  
Microseismic Events ◽  
Mining Face ◽  
Failure Depth

Based on the condition of fully mechanized caving face in one mine, two methods of microseismic monitoring and numerical analysis were combined to study the evolution characteristics and development law of floor failure depth in extra-thick coal seam. Microseismic monitoring results show that the number of microseismic events partly reflects the influence of mining disturbance in the roof and floor rock mass. The distribution of microseismic events are intensive near the coal mining face, which show the floor rock mass is seriously damaged during the coal mining. The greatest floor failure depth estimated from mine microseismic monitoring is 31 meters. Numerical analysis indicate that the rock stress around the mine stope is redistributed during the coal mining, due to the effect of mining disturbance. The abutment pressure increases in front of the coal mining face and the stress reduces in the mined areas. The concentration and release of the stress makes contribution to the destroy of the floor rock. The maximum floor failure depth is up to 28 meters calculated from numerical simulation. The consistency of microseismic monitoring results and numerical analysis improve that it is effective and reliable to obtain floor failure depth and considerably possible to predict the water inrush using microseismic monitoring technology with its inherent ability to remotely monitor the progressive failure caused by mining. The research results have great popularization and application values for the similar mine.

scholarly journals Fracture Propagation and Hydraulic Properties of a Coal Floor Subjected to Thick-Seam Longwalling above a Highly Confined Aquifer

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Shaodong Li ◽  
Gangwei Fan ◽  
Dongsheng Zhang ◽  
Shizhong Zhang ◽  
Liang Chen ◽  
...  
Keyword(s):  
Coal Seam ◽  
Longwall Mining ◽  
Water Pressure ◽  
Water Inrush ◽  
Volumetric Strain ◽  
Longitudinal Direction ◽  
Confined Aquifer ◽  
Floor Rock ◽  
Fracture Development ◽  
Mining Disturbance

The high-pressure and water-rich confined aquifer occurring in the Ordovician limestone sequence poses great threats to the routine production of underground longwall mining. Considering the intense cooperation of mining disturbance and water pressure, water-conducting fractures within a coal seam floor can connect the lower aquifer and upper goaf, and this hydraulic behavior is considered the root of water inrush hazard and water loss or contamination. In this paper, the panel 4301 of the Longquan coal mine serves as the case where the panel works closely above the floor with high water pressure. By the combination of physical and numerical modelling approaches, the variation characteristics of fracture development and volumetric strain of floor rocks subjected to mining disturbance are analyzed. A numerical computation model is constructed based on the volumetric strain-permeability equation obtained by curve fitting, and on such basis, the impacts of different mining parameters on floor rock permeability are studied. The results show that the floor rocks experience fracture generation, extension, and convergence procedures as the workface advances along the longitudinal direction, and fractures appearing in front of the workface are more developed. In the whole process of coal seam extraction, the volumetric strain profile exhibits “Λ” shape and an inverted saddle shape before and after overburden strata collapse. By controlling a single variable, the paper reveals that panel height is of greater impact on floor permeability changes than panel length and panel width.

scholarly journals Research on Stress Distribution and Failure Depth of Mining Floor During the First Weighting of Main Roof

2015 ◽  
Vol 9 (1) ◽  
pp. 763-767
Author(s):  
Bingchao Zhao ◽  
Zhangrong Liu ◽  
Chao Tong
Keyword(s):  
Stress Distribution ◽  
Main Roof ◽  
Failure Criteria ◽  
Elastic Model ◽  
Floor Rock ◽  
Stress Contour ◽  
Coulomb Failure ◽  
Mining Face ◽  
Failure Depth ◽  
Safe Mining

In order to research stress distribution and failure depth of mining floor during the first weighting of main roof, based on the analysis of abutment pressure distribution in this case, an elastic model was established to calculate the stress of any point on the floor. The expressions for this model were deduced, and a failure criterion of floor rock was put forward according to the Mohr-Coulomb failure criteria. Taking the parameters of 3612 mining face of Zhu Zhuang coal mine as an example, and through solving stress distribution of mining floor during its first weighting of main roof, stress contour and failure district of floor were determined . The result showed that, the failure depth of 3612 mining floor is 12.4m, which is rather close to the measured value 13m, thus, the utility and reliability of this study method were effeciently verified. The result provided theoretical basis for bottom grouting strengthening before the first weighting of main roof, and established theoretical foundation for further research on safe mining of confined waters.

The Optimization Research of Wide Strip and Full-Pillar Mining under Villages

2012 ◽  
Vol 616-618 ◽  
pp. 406-410
Author(s):  
Gui Liu ◽  
Hua Xing Zhang ◽  
Jin Hui Chen ◽  
Chao Gao
Keyword(s):  
Surface Structures ◽  
Strip Mining ◽  
Mining Method ◽  
Sequence Optimization ◽  
Wide Strip ◽  
Deformation Limit ◽  
Working Face ◽  
Specific Analysis ◽  
Pillar Mining ◽  
Coal Pillars

By making full use of the advantages of strip mining method and full-pillar mining method, the wide strip and full-pillar mining method can achieve the aim of mining under villages. However, at the full-pillar mining stage, the difficulty in managing several workfaces which are at work at the same time still exists. To improve the wide strip and full-pillar mining method’s applicability, an optimization of extraction sequence for coal pillars instead of the multi-working-face is put forward at the stage of full-pillar mining, and in the case of the deformation limit of surface structures is satisfied, to extract all the coal pillars which are under villages. By specific analysis of the extraction sequence optimization of the coal pillars in No.1 mine under Qian Xudapo village which belongs to Chang Chun coal Co., LTD., a better result is got which also acts a technological reference for the extraction under villages.

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.

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