Optimum position of roadway in the middle residual coal seam between the upper and lower longwall gobs

2021 ◽  
pp. 1-17
Author(s):  
Guorui Feng ◽  
Shengwei Wang ◽  
Yuxia Guo ◽  
Yujiang Zhang ◽  
Jinwen Bai ◽  
...  
Keyword(s):  
Coal Seam ◽  
Optimum Position ◽  
Residual Coal ◽  
Longwall Gobs

scholarly journals Study on the Rheological Failure Mechanism of Weakly Cemented Soft Rock Roadway during the Mining of Close-Distance Coal Seams: A Case Study

2020 ◽  
Vol 2020 ◽  
pp. 1-20
Author(s):  
Wenkai Ru ◽  
Shanchao Hu ◽  
Jianguo Ning ◽  
Jun Wang ◽  
Qingheng Gu ◽  
...  
Keyword(s):  
Coal Seam ◽  
Failure Mechanism ◽  
Coal Pillar ◽  
Soft Rock ◽  
Western China ◽  
Creep Failure ◽  
Mining Areas ◽  
Geological Conditions ◽  
Residual Coal ◽  
Close Distance

During the mining of the shallow-buried and close-distance multiple coal seam, the rheological failure of the surrounding weakly cemented soft rock of the roadway in the lower coal seam under the concentrated stress is very rare. However, the stress on the roof of the upper coal seam is transmitted down through the residual pillar, resulting in this situation. Taking the Gaojialiang coal mine which is located in the mining areas of western China as the research object, the failure mechanism of the roadway roof under the residual coal pillar in the shallow-buried and close-distance multiple seam is studied in combination with field monitoring and numerical simulation. Furthermore, suggestions on the roadway support under such geological conditions are proposed. The results show that the residual coal pillar in the working face of the lower coal seam gradually collapses during the mining of the shallow-buried and close-distance multiple coal seam. The concentrated stress transferred by the coal pillar increases further, which makes the roof stress of the lower coal seam roadway to increase continuously. In addition, the stress of the roadway roof also increases further due to the rotation of the broken rock above the goaf, and the peek region of stress moves to the nongoaf area. Combining the heavy concentrated stress and weakly cemented property, the shallow-buried surrounding rock shows rheological behavior and failure. Therefore, we must pay more attention on the creep failure of the roadway roof under the action of the residual coal pillar even in the shallow-buried coal seam.

scholarly journals Vertical stress and stability of interburden over an abandoned pillar working before upward mining: a case study

2018 ◽  
Vol 5 (8) ◽  
pp. 180346 ◽  
Author(s):  
Jinwen Bai ◽  
Guorui Feng ◽  
Shanyong Wang ◽  
Tingye Qi ◽  
Jian Yang ◽  
...  
Keyword(s):  
Coal Seam ◽  
Initial Stress ◽  
Central Region ◽  
Coal Mine ◽  
Mechanical Analysis ◽  
Field Monitoring ◽  
Vertical Stress ◽  
Plastic Damage ◽  
Residual Coal ◽  
Upward Mining

Upward mining of the residual coal seam over an abandoned pillar working is one of the effective measures to alleviate the contradiction between limited resources and increased consumption. Interburden stability over an abandoned pillar working plays a significant role in guaranteeing the safety of upward mining; however, it has not yet been extensively studied and understood. In this study, the vertical stress of the interburden over an abandoned pillar working was first investigated. The mechanical model of the interburden was established and the damage conditions were analysed. Then, the stability of the interburden over 38502 abandoned workings in Baijiazhuang coal mine was determined by mechanical analysis and field monitoring. The results show that: (i) Vertical stress of the interburden over abandoned mining zones is clearly lower than the initial stress, indicating the existence of a de-stressed effect. Moreover, vertical stress of the interburden over residual coal pillars is greater than the initial stress, which is the evidence of a stress concentration effect. (ii) The interburden over an abandoned pillar working should be regarded as an elastic rectangular plate supported by generalized Kelvin bodies in mechanical modelling. (iii) The interburden over abandoned mining zones may experience two damage stages. In the first stage, initial plastic damage appears at the central region of interburden. In the second stage, the plastic damage evolves from the central point to the surrounding areas. (iv) The mechanical analysis and field monitoring both indicate the initial damage occurred at the central region over 38502 abandoned workings in Baijiazhuang coal mine before upward mining. Related rock control measures should be implemented in that region to guarantee the safe mining of the residual coal seam.

scholarly journals Numerical Investigation into Evolution of Crack and Stress in Residual Coal Pillars under the Influence of Longwall Mining of the Adjacent Underlying Coal Seam

2019 ◽  
Vol 2019 ◽  
pp. 1-18
Author(s):  
Xin Wang ◽  
Yuechao Wu ◽  
Xuehua Li ◽  
Shun Liang
Keyword(s):  
Coal Seam ◽  
Longwall Mining ◽  
Distinct Element ◽  
Movement Characteristics ◽  
Universal Distinct Element Code ◽  
Voronoi Method ◽  
Mining Safety ◽  
Distinct Element Code ◽  
Coal Pillars ◽  
Residual Coal

Longwall mining of the adjacent coal seam with the presence of residual coal pillars overlying the seam can result in abnormal strata pressure and severe overburden failure, which poses a significant threat to mining safety. The threat is mainly manifested in the form of intense coal or rock burst and hazardous interconnection between gobs. This study employed the universal distinct element code (UDEC) to investigate the microscopic failure mechanism of the overlying residual coal pillars under the influence of longwall mining of an adjacent underlying coal seam in Yuanbaowan coal mine, China. Using the Voronoi method, we innovatively visualized the evolution of cracks in residual pillars, revealed the mechanism behind the failure of pillars, and explored the evolution and distribution of abutment stress. Also, strata movement characteristics during underlying panel extraction have been surveyed. Based on the modeling results, effective measures are proposed to ensure safe mining under residual coal pillars. This study might provide a certain reference for safe extraction of multiple seams in Datong Coalfield, China, and also in the central and western Appalachian Basin, United States, where many mining activities are carried out under residual pillars.

Gas Control Technology of Fully Mechanized Caving Face of Hard Desorbing Coal Seam

2013 ◽  
Vol 718-720 ◽  
pp. 1335-1340
Author(s):  
Gang Wang ◽  
Hai Yang Wang ◽  
Xin Hua Zhang
Keyword(s):  
Coal Seam ◽  
Efficient Production ◽  
Control Technology ◽  
Actual Situation ◽  
Coal Face ◽  
Gas Emission ◽  
Investment Cost ◽  
Residual Gas ◽  
Gas Control ◽  
Residual Coal

Basing on the problems of residual coal in goaf in fully mechanized caving face in hard desorbing coal seam, high content of residual gas, large gas emission, serious gas overrun in return airflow corner and vitiated air, combing the actual situation in 3-219 fully mechanized caving face, the paper has adopted adjacent goaf drainage, drainage in gas drainage technology, formed a low investment cost and effective gas control technology and ensured the safe and efficient production in coal face and has a certain reference to control gas of fully mechanized caving face in hard desorbing coal seam.

Research on Reasonable Position of Roadway for close Multi-Seam and its Application

2013 ◽  
Vol 807-809 ◽  
pp. 2393-2397
Author(s):  
Ai Qing Liu
Keyword(s):  
Stress Concentration ◽  
Coal Seam ◽  
Abutment Pressure ◽  
Dynamic Pressure ◽  
Coal Pillar ◽  
Stress Zone ◽  
Concentration Degree ◽  
Residual Coal

The principle of roadway layout is in the low stress zone. Roadway will be difficult to support due to the lower seam face in the close multi-seam is affected by dynamic pressure of the upper seam face mining. The distribution of abutment pressure after the upper seam face mining were analyzed,concluded that: The layout of lower seam roadway should avoid the stress concentration area of residual coal pillar; Stress concentration of the coal pillar is related with mining order, and stress concentration degree is higher in the first mining side of the coal pillar; when the upper coal seam is gob, the layout of the roadway in the lower coal seam with the pattern of homodromous alternate interior layout will be easy to support.

scholarly journals Study on Pressure Relief Technology of High-Pressure Water Jet of Residual Coal Pillar in Overlying Goaf in Close Seam Mining

2022 ◽  
Vol 2022 ◽  
pp. 1-19
Author(s):  
Shang Yang ◽  
Xuehui Li ◽  
Jun Wang ◽  
Shuhao Yang ◽  
Zhen Shen ◽  
...  
Keyword(s):  
High Pressure ◽  
Coal Seam ◽  
Coal Pillar ◽  
Water Jet ◽  
Hydraulic Support ◽  
Working Face ◽  
Pressure Water ◽  
High Pressure Water Jet ◽  
Residual Coal ◽  
Close Distance

To solve the problem of strong ground pressure behaviour under a residual coal pillar in the overlying goaf of a close-distance coal seam, this paper proposes the technology of weakening and relieving the residual coal pillar in the overlying goaf by a high-pressure water jet. Based on the geological occurrence of the No. 3 coal seam and mountain No. 4 coal seam in the Yanzishan coal mine, the high-pressure water jet pressure relief technology of residual coal pillars in the overlying goaf of close-distance coal seams was studied by theoretical analysis and field industrial tests. First, the elastic-plastic zone of the residual coal pillar and the stress distribution law of the floor are obtained by theoretical analysis, and the influence degree of the residual coal pillar on the support of the lower coal seam working face is revealed. Then, a high-pressure water jet combined with mine pressure is proposed to weaken the residual coal pillar. Finally, through the residual coal pillar hydraulic cutting mechanical model and “double-drilling double-slot” model, the high-pressure water jet drilling layout parameters are determined, and an industrial field test is carried out. The single knife cutting coal output and 38216 working face hydraulic support monitoring data show that high-pressure hydraulic slotting can weaken the strength of the coal body to a certain extent, destroy the integrity of the residual coal pillar, cut off the load transmission path of the overlying strata, and reduce the working resistance of the hydraulic support under the residual coal pillar to a certain extent, which is beneficial to the safe mining of the working face.

scholarly journals A Method for Determining Feasibility of Mining Residual Coal above Out-Fashioned Goaf under Variable Load: A Case Study

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Yuxia Guo ◽  
Honghui Yuan ◽  
Xiaogang Deng ◽  
Yujiang Zhang ◽  
Yunlou Du ◽  
...  
Keyword(s):  
Coal Seam ◽  
Coal Mine ◽  
Coal Pillar ◽  
New Method ◽  
System Model ◽  
Variable Load ◽  
Residual Coal ◽  
Seam Mining ◽  
Suspended Roof ◽  
Upward Mining

Out-fashioned goaf is the protective structure for mining the upper residual coal, and its stability is the core problem in mining the upper residual coal. According to the upward mining demand for No. 5 coal seam above the out-fashioned goaf in Baizi Coal Mine, a new method is proposed to determine the upward mining safety. According to the analysis of the actual situation of the mine, the coal pillar and suspended roof in the out-fashioned goaf are taken as the objects. Furthermore, a “coal pillar-suspended roof” system model based on the variable load induced by abutment pressure of upper coal seam mining is established. After the mechanical model was solved, the parameter acquisition method of the model was established. The basic parameters of Baizi Coal Mine were considered to determine the feasibility of mining residual coal above out-fashioned goaf. And the effects of variable load on the coal pillar and suspended roof stability were analyzed. The results show that the upper No. 5 coal seam in Baizi Coal Mine can be mined safely. Compared to the traditional method, which simplifies all the upper loads to uniform loads, the new method is safer. The system stability of the suspended roof and coal pillar is influenced by “a/L” and “L.” Axial stress curves of the coal pillar and suspended roof appear nearly parabolic with “a/L” varying. Their maximum values are obtained when the “a/L” value is around 0.5∼0.6. In this situation, the combination structure is most easy to to be damaged. The ratio q′/q has a linear relationship with all stresses of the system model. The failure sequence of the system model is determined by analyzing the relationship between the tensile strength of the suspended roof and compressive strength of the coal pillar. This study provides a reference case for coal resources upward mining under similar conditions.

scholarly journals Study on Deformation and Energy Release Characteristics of Overlying Strata under Different Mining Sequence in Close Coal Seam Group Based on Similar Material Simulation

Energies ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 4485 ◽  
Author(s):  
Feng Cui ◽  
Chong Jia ◽  
Xingping Lai
Keyword(s):  
Coal Seam ◽  
Energy Release ◽  
Coal Mining ◽  
Fracture Zone ◽  
Seismic Events ◽  
Rock Formation ◽  
Working Face ◽  
Residual Coal ◽  
Overlying Strata ◽  
Loose Rock

For the characteristics of overburden deformation and energy release under different mining sequences of close-distance coal seam groups, physical material similar simulation experiments were carried out, and comprehensive monitoring methods such as dial gauge, total station, micro-seismic monitor, and pressure sensor were used to test the Guangou Coal Mine. The comparative analysis of the initial mining and the upward recovery of the B4-1 coal seam is carried out to study the migration law, mine pressure distribution, and energy release characteristics of the overlying strata during W1145 mining face mining and residual coal mining. The results show that the maximum subsidence of surface and rock formation caused by re-mining of B4-1 residual coal is 0.96 m and 2.57 m respectively, which is 0.42 m and 0.47 m lower than that of W1145 working face. The boundary angle, moving angle, and rock stratum formed by the upward recovery of the remaining coal seam are 79.3°, 81.1°, and 67.5° respectively, which are smaller than the 80.9°, 82.3°, and 75.8° formed by the first mining. The cumulative development height of the fracture zone caused by upward mining is 115.7 m, which is 8.0% smaller than the cumulative development height of the downstream fracture zone of 125.8 m. When the up-level mining is carried out, the fragmentation effect of the rock layer below the key layer is strong, which makes the loosely broken rock block have a better supporting effect. Therefore, the residual coal mining time is longer than that of the first mining. The initial pressure step of the residual coal recovery is 139.2 m, and the average step of the cycle is 34.2 m, which is significantly larger than the 128.0 m and 26.0 m of the first mining. The loose rock strata that are disturbed by the upward recovery are more likely to be broken. Therefore, there are more micro-seismic events during the re-mining of the remaining coal. The B4-1 residual coals have a total of 945 incidents of re-seismic micro-seismic events, which is 292 more than the W1145 working face. After the B2 coal seam mining disturbance, the energy of some rock layers above the B4-1 coal seam is released, so that the micro-seismic energy caused by re-mining of the remaining coal seam is small. Through microseismic monitoring, it can be concluded that the accumulated energy in the process of upward re-mining of remaining coal seam is less than that in the process of downward mining of W1145 working face. Upward recovery is more likely to cause damage in the disturbed loose rock formation. Therefore, the frequency of micro-seismic events during the upward recovery is higher, and the partial energy release of the rock after the disturbance is caused, so that the source energy generated in the unit length of the upward recovery is smaller than the initial one.

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