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MODEL TESTS OF LONGWALL SHEARER WITH STRING FEED SYSTEM

Łukasz Bołoz

Archives of Mining Sciences | 2018 | vol. 63 | No 1 | DOI: 10.24425/118885

Keywords thin seams longwall shearer analytical loadings tests model tests physical and mathematical model of the longwall shearer load on the longwall shearer

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Authors and Affiliations

Łukasz Bołoz

Redevelopment of Fractures and Permeability Changes after Multi-Seam Mining of Shallow Closely Spaced Coal Seams

Zhenqi Liu Xiaoxing Zhong Botao Qin Hongwei Ren Ang Gao

Archives of Mining Sciences | 2019 | vol. 64 | No 4 | 671-686 | DOI: 10.24425/ams.2019.129376

Keywords shallow closely spaced coal seams multi-seam mining fracture redevelopment permeability changes

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Abstract

Mining the lower seams in a sequence of shallow, closely spaced coal seams causes serious air leakage in the upper goaf; this can easily aggravate spontaneous combustion in abandoned coal. Understanding the redevelopment of fractures and the changes in permeability is of great significance for controlling coal spontaneous combustion in the upper goaf. Based on actual conditions at the 22307 working face in the Bulianta coal mine, Particle Flow Code (PFC) and a corresponding physical experiment were used to study the redevelopment of fractures and changes in permeability during lower coal seam mining. The results show that after mining the lower coal seam, the upper and lower goafs become connected and form a new composite goaf. The permeability and the number of fractures in each area of the overlying strata show a pattern of „stability-rapid increase-stability“ as the lower coal seam is mined and the working face advances. Above the central area of goaf, the permeability has changed slightly, while in the open-cut and stop line areas are significant, which formed the main air leakage passage in the composite goaf.

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Authors and Affiliations

Zhenqi Liu

Xiaoxing Zhong

Botao Qin

Hongwei Ren

Ang Gao

Classification and Decision-Making of Fully Mechanised Mining Technology Pattern for Thin Seam

Chen Wang Yu Zhang Yong Liu Chengyu Jiang Mingqing Zhang

Archives of Mining Sciences | 2021 | vol. 66 | No 3 | 333-349 | DOI: 10.24425/ams.2021.138592

Keywords Thin seam Fully mechanised mining technology pattern classification decision-making

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Abstract

As one of the most important decision-making problems in fully mechanised mining, the corresponding mining technology pattern is the technical foundation of the working face. Characterised by complexity in a thin seam fully mechanised mining system, there are different kinds of patterns. In this paper, the classification strategy of the patterns in China is put forward. Moreover, the corresponding theoretical model using neural networks applied for patterns decision-making is designed. Based on the above, optimal selection of these patterns under given conditions is achieved. Lastly, the phased implementation plan for automatic mining pattern is designed. As a result of the industrial test, automatic mining for panel 22204 in Guoerzhuang Coal Mine is realised.

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Bibliography

[1] Li Jianmin, Yan Qingyou, Zhou Zhipo, Application status and development of coal mining technology in China. Coal Science and Technology (10), 55-60 (2012). DOI: https://doi.org/10.13199/j.cst.2012.10.61.lijm.023
[2] Zhao, T., et al., An innovative approach to thin coal seam mining of complex geological conditions by pressure regulation. International Journal of Rock Mechanics and Mining Sciences 71, 249-257 (2014). DOI: https://doi.org/10.1016/j.ijrmms.2014.05.021
[3] Yuan Liang, Research on mining technology and equipment for thin coal seams. Coal Mining (03), 15-18+42 (2011). DOI: https://doi.org/10.13532/j.cnki.cn11-3677/td.2011.03.008349
[4] Satar Mahdevari, Kourosh Shahriar, Mostafa Sharifzadeh, et al. Stability prediction of gate roadways in longwall mining using artificial neural networks 28 (11), 3537-3555 (2017). DOI: https://doi.org/10.1007/s00521-016-2263-2
[5] W. Chen, et al., Optimal Selection of a Longwall Mining Method for a Thin Coal Seam Working Face. Arabian Journal for Science and Engineering 41 (9), 3771-3781(2016). DOI: https://doi.org/10.1007/s13369-016-2260-x
[6] W. Chen PhD thesis, Key technology and decision support system for longwall fully mechanized mining in thin coal seams, China University of Mining and Technology, Xu Zhou, China (2016).
[7] B. Zhang, A. Li, Automated technology research on fully mechanized mining of thin coal seams. Advanced Materials Research 774-776, 1453-1457 (2013). DOI: https://doi.org/10.4028/www.scientific.net/AMR.774-776.1453
[8] D. Shang, et al., Research on Kinematics Joint Type Mobile Robot Platform for Thin Coal Seam Inspection. Applied Mechanics and Materials 651-653, 818-821 (2014). DOI: https://doi.org/10.4028/www.scientific.net/AMM.651-653.818
[9] J. Ralston, et al., Sensing for advancing mining automation capability: A review of underground automation technology development. International Journal of Mining Science and Technology 24 (3), 305-310 (2014). DOI: https://doi.org/10.1016/j.ijmst.2014.03.003.
[10] C. Wang, S. Tu, Selection of an Appropriate Mechanized Mining Technical Process for Thin Coal Seam Mining. Mathematical Problems in Engineering (893232), 1-10 (2015). DOI: https://doi.org/10.1155/2015/893232
[11] P athegama G. Ranjith, Jian Zhao, Minghe Ju, et al. Opportunities and Challenges in Deep Mining: A Brief Review 3 (4), 546-551 (2017). DOI: https://doi.org/10.1016/J.ENG.2017.04.024
[12] Chen Wei, PhD thesis, Research on comprehensive evaluation model of coal mine safety based on neural network, Capital University of Economics and Business, Bei Jing, China (2010).
[13] Xiaofeng Li, Suying Xiang, Pengfei Zhu, et al. Establishing a Dynamic Self-Adaptation Learning Algorithm of the BP Neural Network and Its Applications. 25(14), (2015). DOI: https://doi.org/10.1142/S0218127415400301
[14] M. Madhiarasan, S.N. Deepa. Comparative analysis on hidden neurons estimation in multi layer perceptron neural networks for wind speed forecasting 48 (4), 449-471 (2017). DOI: https://doi.org/10.1007/s10462-016-9506-6
[15] N amig J. Guliyev, E Vugar. Ismailov. Approximation capability of two hidden layer feedforward neural networks with fixed weights (2018). DOI: https://doi.org/10.1016/j.neucom.2018.07.075
[16] B. Yilmaz, M. Dagdeviren, A combined approach for equipment selection: F-PROMETHEE method and zero-one goal programming. Expert Systems with Applications 38 (9), 11641-11650 (2011). DOI: https://doi.org/10.1016/j.eswa.2011.03.043
[17] Daming Yang, Bingjing Li. The Main Adjustment of New Version China’s “Coal Mine Safety Regulations”. International Journal of Oil, Gas and Coal Engineering 7 (2) (2019). DOI: https://doi.org/10.11648/j.ogce.20190702.14
[18] Liu Shouqiang, Wu Qiang, Zeng Yifan. Analysis of revision points of detailed rules for water prevention and control in coal mines. Coal Engineering 51 (03), 1-4 (2019). DOI: https://doi.org/10.11799/ce201903001
[19] R.U. Bilsel, G. Büyüközkan, D. Ruan, A fuzzy preference‐ranking model for a quality evaluation of hospital web sites. International Journal of Intelligent Systems 21 (11), 1181-1197 (2006). DOI : https://doi.org/10.1002/int.20177
[20] R .R. Yager, A procedure for ordering fuzzy subsets of the unit interval. Information Sciences 24 (2): p. 143-161 (1981). DOI: https://doi.org/10.1016/0020-0255(81)90017-7
[21] Yang Qian, Improvement of BP neural network prediction method and its application in long-term settlement prediction of tunnels. Journal of Beijing University of Technology. (01), 92-97 (2011). DOI: CNKI: SUN: BJGD.0.2011-01-016
[22] K. Saito, R. Nakano, Extracting regression rules from neural networks. Neural Networks 15 (PII S0893- 6080(02)00089-810), 1279-1288 (2002). DOI: https://doi.org/10.1016/S0893-6080(02)00089-8
[23] Zhang Dongsheng, Zhang Jixiong, Zhang Xianchen, Fuzzy comprehensive evaluation of mining process conditions of coal seam geological conditions in working face. Journal of Systems Engineering (03), 252-256 (2002). DOI: https://doi.org/10.3969/j.issn.1000-5781.2002.03.011
[24] Zhang Lijun, Zhang Le, Comprehensive Evaluation of Adaptability of Thin Coal Seam Fully Mechanized Mining Technology. Coal Science and Technology (06), 43-45 (2006). DOI: https://doi.org/10.13199/j.cst.2006.06.53.zhanglj.016
[25] C. Wang, S. Tian, Evolving Neural Network Using Genetic Algorithm for Prediction of Longwall Mining Method in Thin Coal Seam Working Face. International Journal of Mining and Mineral Engineering 9 (3), 228-239 (2018). DOI: https://doi.org/10.1504/IJMME.2018.096121

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Authors and Affiliations

Chen Wang

1 2

e-mail:

ORCID:

Yu Zhang

1

e-mail:

ORCID:

Yong Liu

1

e-mail:

ORCID:

Chengyu Jiang

1

e-mail:

ORCID:

Mingqing Zhang

1

e-mail:

ORCID:

Guizhou University, Mining College, Guiyang 550025, China
Chongqing Energy Investment Group Science & Technology co., LTD, Chongqing 400060, China

A Roadway in Close Distance to Coal Seam in Deep Mine: Location Selection and Supporting Practice based on Creep Characteristics of Surrounding Rocks

Xufeng Wang Jiyao Wang Xuyang Chen Zechao Chen

Archives of Mining Sciences | 2021 | vol. 66 | No 3 | 407-419 | DOI: 10.24425/ams.2021.138597

Keywords deep mine close distance coal seam group location of roadway creep

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Abstract

In deep mines, since the broken surrounding rocks & high-stress level of a roadway being near a coal seam, the creep characteristics of surrounding rocks should be considered as the main influencing factor in the selection for the roadway’s location of the lower coal seam. Both VI15 and VI16-17 coal seams of the Pingdingshan No. 4 Coal Mine, in China, Henan province, are close coal seams with a depth of around 900 m. According to the traditional formula calculation results, when the lower coal seam roadway is staggered 10 m to the upper coal seam goaf, the roadway pressure behaviour is significant, and the support becomes difficult. In this paper, the properties of surrounding rock were tested and the influence of lower coal seam on the stress state of surrounding rock is analysed by numerical simulation, and systematic analysis on the stress and creep characteristics of the surrounding rock of the mining roadway and its effects on the deformation is performed. The results demonstrated that the roadway’s locations in the lower coal seam can be initially divided into three zones: the zone with accelerated creep, the transition creep zone and the insignificant creep zone. The authors believed that the roadway layout in an insignificant creep zone can achieve a better supporting effect. Based on the geological conditions of the roadway 23070 of the VI16-17 coal seam of the Pingdingshan No. 4 Coal Mine, combined with the above analysis, a reasonable location of roadway (internal offset of 30 m) was determined using numerical simulation method. The reliability of the research results is verified by field measurement. The above results can provide a reference for selecting the roadway’s location under similar conditions.

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Bibliography

[1] Q .S. Li, X.W. Heng, Optimal Selection Method of Reasonable Mining Program for Close Distance Coal Seams Group. Coal Engineering 47 (10),12-14 (2015). DOI: https://doi.org/10.11799/ce201510004
[2] S.G. Cao, D.J. Zou, Y.J. Bai, P.J. He, H.R. Wu, Surrounding rock control of mining roadway in the thin coal seam group with short distance and “three soft”. Journal of Mining & Safety Engineering 28 (4), 524-529 (2011). DOI: https://doi.org/10.3969/j.issn.1673-3363.2011.04.005419
[3] W. Zhang, D.S. Zhang, D.H. Qi, W.M. Hu, Z.M. He, W.S. Zhang, Floor failure depth of upper coal seam during close coal seams mining and its novel detection method. Energy Exploration & Exploitation 36 (5), 1265-1278 (2018). DOI: https://doi.org/10.1177/0144598717747622
[4] Y . Zhang, C.L. Zhang, C.C. Wei, Y.D. Liu, S.Q. Zhang, J.J. Zhao,. The Study on Roadway Layout in Coordination of Mining Coal Seams Base on Failure of Floor Strata. Trans Tech Publications 889-890, 1362-1374 (2014). DOI: https://doi.org/10.4028/www.scientific.net/AMR.889-890.1362
[5] W. Yang, C.Y. Liu, B.X. Huang, Y. Yang, Determination on Reasonable Malposition of Combined Mining in Close- Distance Coal Seams. Journal of Mining & Safety Engineering 29 (1), 101-105 (2012). DOI: https://doi.org/10.3969/j.issn.1673-3363.2012.01.018
[6] G . Yan, Y.Q. Hu, X. Song, Y.P. Fu, Z. Liu, Y. Yang, Theory and Physical Simulation of Conventional Staggered Distance during Combined Mining of Ultra-close Thin Coal Seam Group. Chinese Journal of Rock Mechanics & Engineering 28 (03), 591-597 (2009). DOI: https://doi.org/10.3321/j.issn:1000-6915.2009.03.019
[7] Y . Yong, S.H. Tu, L.N. Lu, X.T. Ma, G. Jie, Unconventional staggered distance simultaneous mining theory in extremely close and thin coal seams and its application. Procedia Earth & Planetary Science 1 (1), 288-293 (2009). DOI: https://doi.org/10.1016/j.proeps.2009.09.046
[8] Y . Li, S. Zhang, J.Z. Li, X.Y. Yu, Z.Z. Quan, C. Wang, Influence of a Large Pillar on the Optimum Roadway Position in an Extremely Close Coal Seam. Journal of Engineering Science & Technology Review 9 (1), 159-166 (2016). DOI: https://doi.org/10.25103/jestr.091.24
[9] C.L. Ju, G.D. Zhao, F. Gao, Coal Pillar Size of Ultra Closed Distance Seam and Layout of Mining Gateway. Advanced Materials Research 616-618, 465-470 (2012). DOI: https://doi.org/10.4028/www.scientific.net/AMR.616-618.465
[10] D .D. Qin, X.F. Wang, D.S. Zhang, X.Y. Chen, Study on Surrounding Rock-Bearing Structure and Associated Control Mechanism of Deep Soft Rock Roadway Under Dynamic Pressure. J. Sustainability, (2019), DOI: https://doi.org/10.3390/su11071892
[11] T. Majcherczyk, P. Małkowski, Z. Niedbalski, Rock Mass Movements Around Development workings in various density of standing-and-roof-bolting support. Journal of Coal Science and Engineering (China) 14 (3), 356-360 (2008). DOI: https://doi.org/10.1007/s12404-008-0078-1
[12] T. Majcherczyk, Z. Niedbalski, P. Małkowski, Ł. Bednarek, Analysis of yielding steel arch support with rock bolts in mine roadways stability aspect. Archives of Mining Sciences 59 (3), 641-654 (2014). DOI: https://doi.org/10.2478/amsc-2014-0045
[13] P. Małkowski, Z. Niedbalski, T. Majcherczyk, Ł. Bednarek, Underground monitoring as the best way of roadways support design validation in a long time period. J. Mining of Mineral Deposits 14 (3), 1-14 (2020). DOI : https://doi.org/10.33271/mining14.03.001
[14] X. Sun, A yielding bolt-grouting support design for a soft-rock roadway under high stress: a case study of the Yuandian No. 2 coal mine in China. Journal of the Southern African Institute of Mining and Metallurgy 118 (1), 71-82 (2018). DOI: https://doi.org/10.17159/2411-9717/2018/v118n1a9
[15] Y . Yu, W. Shen, J. Gao, Deformation mechanism and control of lower seam roadway of contiguous seams. Journal of Mining & Safety Engineering 33 (01),49-55 (2016). DOI: https://doi.org/10.13545/j.cnki.jmse.2016.01.008
[16] H . Yan, M. Weng, R. Feng, W.K. Li, Layout and support design of a coal roadway in ultra-close multiple-seams. Journal of Central South University 22 (11), 4385-4395 (2015). DOI: https://doi.org/ 10.1007/s11771-015-2987-7
[17] Y .J. Qi, Q.H. Jiang, Z.J. Wang, C.B. Zhou, 3D creep constitutive equation of modified Nishihara model and its parameters identification. Chinese Journal of Rock Mechanics and Engineering 31 (2), 347-355 (2012). DOI: https://doi.org/10.3969/j.issn.1000-6915.2012.02.014
[18] A.M. Kovrizhnykh, Deformation and failure of open and underground mine structures under creep. Journal of Mining Science 45 (6), 541-550 (2009). DOI: https://doi.org/10.1007/s10913-009-0068-8
[19] I . Paraschiv-Munteanu, N.D. Cristescu, Stress relaxation during creep of rocks around deep boreholes. International Journal of Engineering Science 39 (7), 737-754 (2001). DOI: https://doi.org/10.1016/S0020-7225(00)00060-4
[20] H . Wang, W.Z. Chen, Q.B. Wang, P.Q.Zheng, Rheological properties of surrounding rock in deep hard rock tunnels and its reasonable support form. Journal of Central South University 23 (4), 898-905 (2016). DOI: https://doi.org/0.1007/s11771-016-3137-6

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Authors and Affiliations

Xufeng Wang

1

e-mail:

ORCID:

Jiyao Wang

1

e-mail:

ORCID:

Xuyang Chen

1

e-mail:

ORCID:

Zechao Chen

1

e-mail:

ORCID:

Jiangsu Engineering Laboratory of Mine Earthquake Monitoring and Prevention, School of Mines, China University of Mining and Technology, Xuzhou 221116, China

Tectonic-climatic interactions during changes of depositional environments in the Carpathian foreland: An example from the Neogene of central Poland

Marek Widera Tomasz Zieliński Lilianna Chomiak Piotr Maciaszek Robert Wachocki Achim Bechtel Barbara Słodkowska Elżbieta Worobiec Grzegorz Worobiec

Acta Geologica Polonica | vol. 71 | No 4 | 519-542 | DOI: 10.24425/agp.2020.134567

Keywords River type Lignite seam Sedimentology Tectonics climate Miocene

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Abstract

Many geological problems have not been convincingly explained so far and are debatable, for instance the origin and changes of the Neogene depositional environments in central Poland. Therefore, these changes have been reconstructed in terms of global to local tectonic and climatic fluctuations. The examined Neogene deposits are divided into a sub-lignite unit (Koźmin Formation), a lignite-bearing unit (Grey Clays Member), and a supra-lignite unit (Wielkopolska Member). The two lithostratigraphic members constitute the Poznań Formation. The results of facies analysis show that the Koźmin Formation was deposited by relatively high-gradient and well-drained braided rivers. Most likely, they encompassed widespread alluvial plains. In the case of the Grey Clays Member, the type of river in close proximity to which the mid-Miocene low-lying mires existed and then were transformed into the first Mid-Miocene Lignite Seam (MPLS-1), has not been resolved. The obtained results confirm the formation of the Wielkopolska Member by low-gradient, but mostly well-drained anastomosing or anastomosing-to-meandering rivers. The depositional evolution of the examined successions depended on tectonic and climatic changes that may be closely related to the mid-Miocene great tectonic remodelling of the Alpine-Carpathian orogen. This resulted in palaeogeographic changes in its foreland in the form of limiting the flow of wet air and water masses from the south and vertical tectonic movements.

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Authors and Affiliations

Marek Widera

1

Tomasz Zieliński

1

Lilianna Chomiak

1

Piotr Maciaszek

2

Robert Wachocki

3

Achim Bechtel

4

Barbara Słodkowska

5

Elżbieta Worobiec

6

Grzegorz Worobiec

6

Adam Mickiewicz University, Institute of Geology, Krygowskiego 12, 61-680 Poznań, Poland
Polish Geological Institute – National Research Institute, Marine Geology Branch, Kościerska 5, 80-328 Gdańsk, Poland
Konin Lignite Mine, 600-lecia 9, 62-540 Kleczew, Poland
Montanuniversitaet Leoben, Austria, Department of Applied Geosciences and Geophysics, Peter-Tunner-Str. 5, A-8700 Leoben, Austria
Polish Geological Institute – National Research Institute, Rakowiecka 4, 00-975 Warszawa, Poland
W. Szafer Institute of Botany, Polish Academy of Sciences, Lubicz 46, 31-512 Kraków, Poland

Case Study: Mechanism and Effect Analysis of Presplitting Blasting in Shallow Extra-Thick Coal Seam

Qiang Sun Chengfang Shan Zhongya Wu Yunbo Wang

Archives of Mining Sciences | 2022 | vol. 67 | No 3 | 381-399 | DOI: 10.24425/ams.2022.142406

Keywords Shallow-buried thick coal seam hard roof and coal seam fully mechanised top coal caving mining blasting presplitting parameter optimisation

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Abstract

The caving effect of the top coal caving is crucial for efficient mining. Using the Yushuling coal mine, Xinjiang province, China, as a case study, the coal and rock physical and mechanical parameters, such as the compressive, tensile, and shear strength values and hardness of the top coal and roof rock, were determined. The analysis of the effect of different factors on the blasting presplitting process was numerically simulated, and the optimal parameters of blast drilling were identified. Three presplit boreholes were implemented: in the workface, the workface’s advance area, and the two roadway roofs in the workface’s advance area. The optimal blasting drilling parameters and charge structure were designed. The field test results in the mine under study indicated that the top coal recovery rate of the 110501 fully mechanised top coal caving face was improved twice (from 40 to more than 80%), and an effective blasting presplitting was achieved. The proposed blasting presplitting method has an important guiding significance for fully mechanised top coal caving mining in Xinjiang and similar mining areas.

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Authors and Affiliations

Qiang Sun

1

e-mail:

ORCID:

Chengfang Shan

2

e-mail:

ORCID:

Zhongya Wu

1

e-mail:

ORCID:

Yunbo Wang

1

e-mail:

ORCID:

China University of Mining and Technology, China
Kuqa Yushuling Coal Mine Co., Ltd, Kuqa, Aksu, China

Deformation and Failure Mechanisms and Support Structure Technologies for Goaf-Side Entries in Steep Multiple Seam Mining Disturbances

Panshi Xie Yongping Wu

Archives of Mining Sciences | 2019 | vol. 64 | No 3 | 561-574 | DOI: 10.24425/ams.2019.129369

Keywords steep seam group goaf-side entry asymmetrical deformation arching effect asymmetrical coupled support structure

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Abstract

Entries in steeply pitching seams have a more complex stress environment than those in flat seams. This study targets techniques for maintaining the surrounding rock mass stability of entries in steep seams through a case study of a steep-seam entry at a mine in southern China. An in-depth study of the deformation and instability mechanisms of the entry is conducted, employing field measurement, physical simulation experiment, numerical simulation, and theoretical analysis. The study results show that the surrounding rock mass of the entry is characterised by asymmetrical stress distribution, deformation, and failure. Specifically, 1) the entry deformation is characterised by a pattern of floor heaving and roof subsidence; 2) broken rock zones in the two entry walls are larger than those in the roof and floor, and the broken rock zone in the seam-floor side wall is larger than that in the seam-roof side wall; 3) rock bolts in the middle-bottom part of the seam-floor side wall of the entry are prone to failure due to tensile stress; and 4) rock bolts in the seam-roof side wall experience relatively even load and relatively small tensile stress. Through analysis, disturbances were found to occur in both temporal and spatial dimensions. Specifically, in the initial mining stage, the asymmetrical rock structure and stress distribution cause entry deformation and instability; during multiple-seam multiple-panel mining operations, a wedge-shaped rock mass and a quasi-arc cut rock stratum formed in the mining space may cause subsidence in the seam-floor side wall of the entry and inter-stratum transpression, deformation, and instability of the entry roof and floor. The principles for controlling the stability of the surrounding rock mass of the entry are proposed. In addition, an improved asymmetrical coupled support structure design for the entry is proposed to demonstrate the effective control of entry deformation.

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Authors and Affiliations

Panshi Xie

Yongping Wu

e-mail:

ORCID:

Internal Mechanism of Asymmetric Deformation and Failure Characteristics of the Roof for Longwall Mining of a Steeply Dipping Coal Seam

Shenghu Luo Tong Wang Yongping Wu Jingyu Huangfu Huatao Zhao

Archives of Mining Sciences | 2021 | vol. 66 | No 1 | 101-124

Keywords steeply dipping seam gangue slip filling deformation failure main roof angle effect

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Abstract

Stability control of the roof is the key to safe and efficient mining of the longwall working face for a steeply dipping coal seam. In this study, a comprehensive analysis was performed on the roof destruction, migration, and filling characteristics of a steeply dipping longwall working face in an actual coalmine. Elastic foundation theory was used to construct a roof mechanics model; the effect of the coal seam inclination angle on the asymmetric deformation and failure of the roof under the constraint of an unbalanced gangue filling was considered. According to the model, increasing the coal seam angle, thickness of the immediate roof, and length of the working face as well as decreasing the thickness of the coal seam can increase the length of the contact area formed by the caving gangue in the lower area of the slope. Changes to the length of the contact area affect the forces and boundary conditions of the main roof. Increasing the coal seam angle reduces the deformation of the main roof, and the position of peak deflection migrates from the middle of the working face to the upper middle. Meanwhile, the position of the peak rotation angle migrates from the lower area of the working face to the upper area. The peak bending moment decreases continuously, and its position migrates from the headgate T-junction to the tailgate T-junction and then the middle of the working face. Field test results verified the rationality of the mechanics model. These findings reveal the effect of the inclination coal seam angle on roof deformation and failure and provide theoretical guidance for engineering practice.

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Bibliography

[1] Y.P. Wu, D.F Yun, P.S. Xie et al., Progress, practice and scientific issues in steeply dipping coal seams fullymechanized mining. J. China Coal Soc. 45 (01):24-34 (2020) (in Chinese).
[2]. Y.P. Wu, B.S. Hu, D Lang et al., Risk assessment approach for rockfall hazards in steeply dipping coal seams. Int. J. Rock Mech. Min. Sci. 138, 104626 (2021). doi: 10.1016/j.ijrmms.2021.104626
[3] D .Y. Zhu, W.L. Gong, Y. Su et al., Application of High-Strength Lightweight Concrete in Gob-Side Entry Retaining in Inclined Coal Seam. Advances in Materials Science and Engineering (2020). doi: 10.1155/2020/8167038
[4] H .W. Wang, Y.P. Wu, J.Q. Jiao et al., Stability Mechanism and Control Technology for Fully Mechanized Caving Mining of Steeply Inclined Extra-Thick Seams with Variable Angles. Mining, Metall. Explor. (2020). doi: 10.1007/ s42461-020-00360-0
[5] R .A. Frumkin, Predicting rock behaviour in steep seam faces (in Russian). International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 20 (1), A12-A13 (1983). doi: 10.1016/0148-9062(83)91717-5
[6] A. Ladenko, Improvements in working steep seams. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 11 (12), 247. (1974). doi: 10.1016/0148-9062(74)92108-1
[7] Z. Rak, J. Stasica, Z. Burtan et al., Technical aspects of mining rate improvement in steeply inclined coal seams: A case study. Resources 9 (12), 1-16 (2020). doi: 10.3390/resources9120138
[8] H .S. Tu, S.H. Tu, C. Zhang et al., Characteristics of the Roof Behaviours and mine pressure manifestations during the mining of steep coal seam. Arch. Min. Sci. 62 (4), 871-890 (2020).
[9] P .S. Xie, Y.P. Wu, Deformation and failure mechanisms and support structure technologies for goaf-side entries in steep multiple seam mining disturbances. Arch. Min. Sci. 64 (3), 561-574 (2019). doi: 10.24425/ams.2019.129369
[10] Z.Y.Wang, L.M. Dou, J. He et al., Experimental investigation for dynamic instability of coal-rock masses in horizontal section mining of steeply inclined coal seams. Arabian Journal of Geosciences 13, 15 (2020). doi: 10.1007/ s12517-020-05753-5
[11] P .S. Xie, Y. Luo, Y.P. Wu et al., Roof Deformation Associated with Mining of Two Panels in Steeply Dipping Coal Seam Using Subsurface Subsidence Prediction Model and Physical Simulation Experiment. Mining, Metall. Explor. 37 (2), 581-591 (2020). doi: 10.1007/s42461-019-00156-x
[12] X.P. Lai, H. Sun, P.F. Shan et al., Structure instability forecasting and analysis of giant rock pillars in steeply dipping thick coal seams. Int. J. Miner. Metall. Mater. 22 (12), 1233-1244 (2015). doi: 10.1007/s12613-015-1190-z
[13] Y.P. Wu, B.S. Hu, P.S. Xie, A New Experimental System for Quantifying the Multidimensional Loads on an on-Site Hydraulic Support in Steeply Dipping Seam Mining. Exp. Tech. 43 (5), 571-585 (2019). doi: 10.1007/s40799-019- 00304-4
[14] Y.D. Zhang, J.Y. Cheng, X.X. Wang et al., Thin plate model analysis on roof break of up-dip or down-dip mining stope. J. Min. Saf. Eng. 27 (4), 487 (2010) (in Chinese).
[15] J.R. Cao, L.M. Dou, G.A. Zhu et al., Mechanisms of Rock Burst in Horizontal Section Mining of a Steeply Inclined Extra-Thick Coal Seam and Prevention Technology. Energies 13 (22), 6043 (2020). doi: 10.3390/en13226043
[16] H .W. Wang, Y.P. Wu, M. Liu et al., Roof-breaking mechanism and stress-evolution characteristics in partial backfill mining of steeply inclined seams. Geomatics, Natural Hazards and Risk 11 (1), 2006-2035 (2020). doi: 10.1080/1 9475705.2020.1823491
[17] S.R. Islavath, D. Deb, H. Kumar, Numerical analysis of a longwall mining cycle and development of a composite longwall index. Int. J. Rock Mech. Min. Sci. 89, 43-54 (2016).
[18] H . Basarir, O.I. Ferid, O. Aydin, Prediction of the stresses around main and tail gates during top coal caving by 3D numerical analysis. Int. J. Rock Mech. Min. Sci. 76, 88-97 (2015). doi: 10.1016/j.ijrmms.2015.03.001
[19] J.A. Wang, J.L. Jiao, Criteria of support stability in mining of steeply inclined thick coal seam. Int. J. Rock Mech. Min. Sci. 82, 22-35 (2016). doi: 10.1016/j.ijrmms.2015.11.008
[20] W.Y. Lv, Y.P. Wu, M. Liu et al., Migration law of the roof of a composited backfilling longwall face in a steeply dipping coal seam. Minerals 9 (3) (2019). doi: 10.3390/min9030188
[21] C.F. Huang, Q. Li, S.G.Tian, Research on prediction of residual deformation in goaf of steeply inclined extra- thick coal seam. PLoS ONE 15, 1-14 (2020). doi: 10.1371/journal.pone.0240428
[22] Y.C. Yin, J.C. Zou, Y.B. Zhang et al., Experimental study of the movement of backfilling gangues for goaf in steeply inclined coal seams. Arabian Journal of Geosciences 11 (12) (2018). doi: 10.1007/s12517-018-3686-0
[23] G .S.P Singh, U.K. Singh, Prediction of caving behavior of strata and optimum rating of hydraulic powered support for longwall workings. Int. J. Rock Mech. Min. Sci. 47, 1-16 (2010).
[24] P .S. Xie, Y.Y. Zhang, S.H. Luo et al., Instability Mechanism of a Multi-Layer Gangue Roof and Determination of Support Resistance Under Inclination and Gravity. Mining, Metall. Explor. 37 (5), 1487-1498 (2020). doi: 10.1007/ s42461-020-00252-3
[25] G .J. Wu, W.D. Chen, S.P. Jia et al., Deformation characteristics of a roadway in steeply inclined formations and its improved support. Int. J. Rock Mech. Min. Sci. 130, 104324 (2020). doi: 10.1016/j.ijrmms.2020.104324
[26] Y.Q. Long, Numerical computation of beam on elastic foundation. People’s Education Press, Beijing (1981).

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Authors and Affiliations

Shenghu Luo

1

e-mail:

ORCID:

Tong Wang

2

e-mail:

ORCID:

Yongping Wu

2

e-mail:

ORCID:

Jingyu Huangfu

2

e-mail:

ORCID:

Huatao Zhao

3

e-mail:

ORCID:

Xi’an University of Science and Technology, Department of Mechanics, China
Xi’an University of Science and Technology, School of Energy Engineering, China
Shandong Mining Machinery Group Co., Ltd. China

An expert system for equipment selection of thin coal seam mining

Chen Wang Jie Chen Cheng Liu Chengyu Jiang

Gospodarka Surowcami Mineralnymi - Mineral Resources Management | 2019 | vol. 35 | No 3 | 143-162 | DOI: 10.24425/gsm.2019.128527

Keywords expert system thin coal seam equipment selection and matching decision-making software field applications

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Abstract

As one of the key techniques in the fully mechanized mining process, equipment selection and matching has a great effect on security, production and efficiency. The selection and matching of fully mechanized mining equipment in thin coal seam are restricted by many factors. In fully mechanized mining (FMM) faced in thin coal seams (TCS), to counter the problems existing in equipment selection, such as many the parameters concerned and low automation, an expert system (ES) of equipment selection for fully mechanized mining longwall face was established. A database for the equipment selection and matching expert system in thin coal seam, fully mechanized mining face has been established. Meanwhile, a decision-making software matching the ES was developed. Based on several real world examples, the reliability and technical risks of the results from the ES was discussed. Compared with the field applications, the shearer selection from the ES is reliable. However, some small deviations existed in the hydraulic support and scraper conveyor selection. Then, the ES was further improved. As a result, equipment selection in fully mechanized mining longwall face called 4301 in the Liangshuijing coal mine was carried out by the improved ES. Equipment selection results of the interface in the improved ES is consistent with the design proposal of the 4301 FMM working face. The reliability of the improved ES can meet the requirements of the engineering. It promotes the intelligent and efficient mining of coal resources in China.

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Authors and Affiliations

Chen Wang

e-mail:

ORCID:

Jie Chen

Cheng Liu

Chengyu Jiang

e-mail:

ORCID:

Dynamic elastic properties of the hard coal seam at a depth of around 1260 m

Krzysztof Krawiec

Gospodarka Surowcami Mineralnymi - Mineral Resources Management | 2021 | vol. 37 | No 3 | 159-176 | DOI: 10.24425/gsm.2021.138658

Keywords dynamic elastic parameters coal seam P-wave velocity S-wave velocity seismic profiling

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Abstract

The knowledge of the dynamic elastic properties of a coal seam is important in the context of various types of calculations of the seam behavior under various stress-strain conditions. These properties are often used in numerical and analytical modeling related to maintaining the stability of excavations and the analysis of mechanisms, e.g. related to the risk of rock bursts. Additionally, during the implementation of seismic surveys, e.g. seismic profiling and seismic tomography in coal seams, the reference values of the elastic properties of coal are used in the calculation of relative stresses in various geological and mining conditions.
The study aims to calculate the dynamic elastic parameters of the coal seam located at a depth of 1,260 m in one of the hard coal mines in the Upper Silesian Coal Basin (USCB). Basic measurements of the velocity of P- and S-waves were conducted using the seismic profiling method. These surveys are unique due to the lack of the velocity wave values in the coal seam at such a great depth in the USBC and difficult measurement conditions in a coal mine. As a result, dynamic modulus of elasticity was calculated, such as Young’s modulus, volumetric strain modulus, shear modulus and Poisson’s ratio. The volumetric density of coal used for calculations was determined on the basis of laboratory tests on samples taken in the area of the study. The research results showed that the calculated mean P-wave velocity of 2,356 m/s for the depth of 1,260 m is approximately consistent with the empirical relationship obtained by an earlier study. The P-wave velocity can be taken as the reference velocity at a depth of approx. 1,260 m in the calculation of the seismic anomaly in the seismic profiling method.

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Bibliography

Brown, E.T. and Hoek, E. 1978. Trends in relationships between measured in-situ stresses and depth. Int. J. Rock Mech. Min. Sci. Geomech. Abstr. 15(4), pp. 211–215.

Chlebowski, D. and Burtan, Z. 2021. Geophysical and analytical determination of overstressed zones in exploited coal seam: A case study. Acta Geophys. 69, pp. 701–710. DOI: 10.1007/s11600-021-00547-z.

Czarny et al. 2016 – Czarny, R., Marcak, H., Nakata, N., Pilecki, Z. and Isakow, Z. 2016. Monitoring velocity changes caused by underground coal mining using seismic noise. Pure. Appl. Geophys. 173, pp. 1907–1916. DOI: 10.1007/s00024-015-1234-3.

Dubiński, J. 1989. Seismic method of shock hazard assessment in hard coal mines (Sejsmiczna metoda wyprzedzającej oceny zagrożenia wstrząsami górniczymi w kopalniach węgla kamiennego). Prace Głównego Instytutu Górnictwa. Katowice: Central Mining Institute, 163 pp. (in Polish).

Dubiński, J. and Konopko, W. 2000. Rock bursts – assessment, prognosis, defeating (Tąpania – ocena, prognoza, zwalczanie). Katowice: Central Mining Institute, 378 pp. (in Polish).

Dubiński et al. 2001 – Dubiński, J., Pilecki, Z. and Zuberek, W. 2001. Geophysical research in mines – past, present and future plans (Badania geofizyczne w kopalniach – przeszłość, teraźniejszość, i zamierzenia na przyszłość). Kraków: MEERI PAS (in Polish).

Gustkiewicz, J. ed. 1999. Physical properties of Carboniferous rocks of the Upper Silesian coal basin. Rocks of Saddle beds (Właściwości fizyczne wybranych skał karbońskich Górnośląskiego Zagłębia Węglowego – skały warstw siodłowych). Kraków: MEERI PAS, 267 pp. (in Polish).

ISO 349:2020 Hard coal – Audibert-Arnu dilatometer test.

Jarzyna et al. 2020 – Jarzyna, J., Niculescu, B., M., Malinowski, M. and Pilecki Z. 2020. Editorial for special issue advances in engineering, environmental and mining geophysics. Acta Geophys. 69(2), pp. 609–611. DOI: 10.1007/s11600-021-00560-2.

Kokowski et al. 2019 – Kokowski, J., Szreder, Z. and Pilecka, E. 2019. Reference P-wave velocity in coal seams at great depths in Jastrzebie coal mine. E3S Web of Conf. 133, 01011. DOI: 10.1051/e3sconf/201913301011.

Kudyk, M. and Pilecki Z. 2009. Modulus of deformation of Carpathian flysch on the route of the “Emilia” tunnel in the Zywiec Beskids (Modul deformacji utworow fliszu karpackiego na trasie tunelu „Emilia” w Beskidzie Zywieckim). Zeszyty Naukowe IGSMiE PAN 76, pp. 45–64 (in Polish).

Ladanyi, B. 1974. Use of the long-term strength concept in the determination of ground pressure on tunnel linings. Proceedings of the Third Congress of the Int. Soc. for Rock Mech., Denver, vol. II part B, pp. 1150–1156.

Majcherczyk, T. and Małkowski, P. 2002. Relation between carbon rock depth and behavior of rock mass around openings (Głębokość zalegania skał karbońskich a zachowanie się górotworu wokół wyrobiska korytarzowego). Proceedings of the Conference of Winter School of Rock Mass Mechanics (XXV Zimowa Szkoła Mechaniki Górotworu). Zakopane, 18–22 March, 2002, pp. 427–435 (in Polish).

Majcherczyk et al. 2012 – Majcherczyk, T., Pilecki, Z., Niedbalski, Z., Pilecka, E., Blajer, M. and Pszonka, J. 2012. Impact of geological, engineering and geotechnical conditions on the selection of parameters of the initial support of the road tunnel in Laliki (Wpływ warunków geologiczno-inżynierskich i geotechnicznych na dobór parametrów obudowy wstępnej tunelu drogowego w Lalikach). Gospodarka Surowcami Mineralnymi – Mineral Resources Management 28(1), pp. 103–124 (in Polish).

Małkowski et al. 2021 – Małkowski, P., Niedbalski, Z. and Balarabe, T. 2021. A statistical analysis of geomechanical data and its effect on rock mass numerical modeling: a case study. Int. J Coal Sci. Technol. 8(2), pp. 312–323.

Marcak, H. and Pilecki, Z. 2019. Assessment of the subsidence ratio be based on seismic noise measurements in mining terrain. Arch. Min. Sci. 64, pp. 197–212, DOI: 10.24425/ams.2019.126280.

Olechowski et al. 2018 – Olechowski, S., Krawiec, K., Kokowski, J., Szreder, Z., Harba, P. and Ćwiękała, M. 2018. Comparison of the results of the seismic profiling and WAS-96/RMS seismoacoustic active method in an assessment of the impact of the overlying coal seam edge. E3S Web of Conf. 66, 01011. DOI: 10.1051/e3sconf/20186601011.

PN-G-97002:2018-11 Węgiel kamienny – Klasyfikacja – Typy.

Pilecki, Z. 1995. An Example of Rock Burst Hazard State Control Using a Z onal Seismoacoustic Observation. Proc. Fifth Conf. on Acoustic Emission/Microseismic Activity, Clausthal-Zellerfeld: Trans. Tech. Publications, pp. 313–332.

Pilecki, Z. 1999. Dynamic analysis of mining tremor impact on excavation. [In:] Detournay, C. and Hart, R. eds. Proc. Int. FLAC Symp. on Numerical Modeling in Geomechanics. Minneapolis, Minnesota, USA: 1–3 September, 1999. Rotterdam: A. A. Balkema, pp. 397–400.

Pilecki, Z. 2018. Seismic method in geoengineering (Metoda sejsmiczna w geoinżynierii). Kraków: MEERI PAS, 311 pp. (in Polish).

Szreder et al. 2008 – Szreder, Z., Pilecki, Z. and Kłosiński, J. 2008. Effectiveness of recognition of exploitation edge influence with the help of profiling of attenuation and velocity of seismic wave (Efektywność rozpoznania oddziaływania krawędzi eksploatacyjnych metodami profilowania tłumienia oraz prędkości fali sejsmicznej). Gospodarka Surowcami Mineralnymi – Mineral Resources Management 24(2), pp. 215–226 (in Polish).

Szreder, Z. and Barnaś, M. 2017. Assessment of the impact of an overlying coal seam edge using seismic profiling of refracted P-wave velocity. E3S Web of Conf. 24, 01007 DOI: 10.1051/e3sconf/20172401007.

Ślizowski et al. 2013 – Ślizowski, J., Pilecki, Z., Urbańczyk, K., Pilecka, E., Lankof, L. and Czarny, R. 2013. Site assessment for astroparticle detector location in evaporites of the Polkowice-Sieroszowice copper ore mine, Poland. Adv. High Energy Phys. 12, pp. DOI: 10.1155/2013/461764.

Wojtecki et al. 2016 – Wojtecki, Ł., Dzik, G. and Mirek, A. 2016. Changes of te dynamic elastic modules of the coal seam ahead the longwall face (Zmiany dynamicznych modułów sprężystości pokładu węgla przed frontem ściany). Przegląd Górniczy 72(1), pp. 57–62 (in Polish).

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Authors and Affiliations

Krzysztof Krawiec

1

e-mail:

ORCID:

Mineral and Energy Economy Research Institute, Polish Academy of Sciences, Kraków, Poland

Laser Weld Seam Curved Path Effect on 6063 Aluminum Alloy Strength and Temperature Distributions: COMSOL Numerical Simulation

Aiyong Cui Haodong Liu Shaodong Gao Huakai Wei Jialei Zhao

Archives of Metallurgy and Materials | 2024 | vol. 69 | No 1 | 209-215 | DOI: 10.24425/amm.2024.147810

Keywords 6063 aluminum alloy laser welding irregular weld seam COMSOL numerical simulation mechanical properties

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Abstract

To improve the welding performance of aluminum alloys, a thermal source model of an irregular weld seam was established. COMSOL software was used for numerical simulation of the weld seam geometry effect on the temperature and stress fields in laser welding, which results were experimentally validated. The results show that the ellipsoidal laser welding melted micropool exhibited quasi-steady-state temperature field characteristics. The temperature gradient and thermal stress showed an increase followed by a decline. The temperature fluctuation amplitude of the square-tooth-shaped weld seam exceeded that of the arc-toothshaped one. The temperature evolution of the broken line tooth-shaped weld seam showed a slightly increasing trend, except for the inflection point. The experimental average tensile strength of the weld seam was the highest, reaching about 210 MPa, i.e., roughly 85% of the base material (245 MPa), which coincided with the COMSOL-based temperature field simulation results. With increasing deformation amplitude and transition radius, the maximum tensile force, tensile strength, and elongation at fracture showed an increasing trend. However, the deformation amplitude should be below a certain limit because its increase elongates the welding path and reduces the distance between weld seams, resulting in serious heat accumulation. The tensile fracture morphology of the 6063-T6 base material was curved shear, with shallow toughness pits, small tearing edges at the edges, and small granular objects, indicating small plastic deformation during the fracture process. The tensile fracture of the welded part spanned the weld seam and the base material, and the fracture occurred along the tangent direction of the weld seam. The fracture surface was smooth, the tearing edges at the edge of the toughness pit shifted along the weld seam direction, forming many co-directional slip bands, with highly pronounced plastic deformation.

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Authors and Affiliations

Aiyong Cui

1

e-mail:

ORCID:

Haodong Liu

1

e-mail:

ORCID:

Shaodong Gao

2

e-mail:

ORCID:

Huakai Wei

1

e-mail:

ORCID:

Jialei Zhao

2

e-mail:

ORCID:

Naval Aeronautical University, Qingdao, 266041, China
Liaoning University of Technology, Jinzhou, 121001, China

Dip-Angle-Effect-Based Deformation and Failure Law of Steeply Dipping Stope Roofs with Large Mining Heights

Panshi Xie Baofa Huang Yongping Wu Shenghu Luo Tong Wang Zhuangzhuang Yan Jianjie Chen

Archives of Mining Sciences | 2023 | vol. 68 | No 3 | 507-524 | DOI: 10.24425/ams.2023.146865

Keywords Steeply dipping coal seam large mining height working face dip angle effect stabilitycontrol of the roof support-surrounding rock

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Abstract

The deformation and failure law of stope roofs is more complicated than horizontal coal seams affected by the angle of the coal seam during the mining process of steeply dipping coal seams. This study focused on and analysed the working face of a 2130 coal mine with steep dipping and large mining height. Through the use of numerical calculation, theoretical analysis, physical similar material simulation experiments, and field monitoring, the distribution characteristics of roof stress, as well as the threedimensional caving migration and filling law, in large mining height working faces under the dip angle effect was investigated. The influence mechanism of the dip angle change on the roof stability of large mining heights was investigated. The results revealed that the roof stress was asymmetrically distributed along the inclination under the action of the dip angle, which resulted in roof deformation asymmetry. With the increase in the dip angle, the rolling and sliding characteristics of roof-broken rock blocks were more obvious. The length of the gangue support area increased, the unbalanced constraint effect of the filling gangue on the roof along the dip and strike was enhanced, and the height of the caving zone decreased. The stability of the roof in the lower inclined area of the working face was enhanced, the failure range of the roof migrated upward, and the damage degree of the roof in the middle and upper areas increased. Furthermore, cross-layer, large-scale, and asymmetric spatial ladder rock structures formed easily. The broken main roof formed an anti-dip pile structure, and sliding and deformation instability occurred, which resulted in impact pressure. This phenomenon resulted in the dumping and sliding of the support. The ‘support-surrounding rock’ system was prone to dynamic instability and caused disasters in the surrounding rock. The field measurement results verified the report and provided critical theoretical support for field engineering in practice.

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Authors and Affiliations

Panshi Xie

1 2

Baofa Huang

1 2

Yongping Wu

1 2

e-mail:

ORCID:

Shenghu Luo

2 3

e-mail:

ORCID:

Tong Wang

1 2

e-mail:

ORCID:

Zhuangzhuang Yan

1 2

Jianjie Chen

4

Xi’an University of Science and Technology, School of Energy Engineering, Xi’an 710054, China
Xi’an University of Science and Technology, Key Laboratory of Western Mine Exploitation and Hazard Prevention Ministry of Educat ion, Xi’an 710054, China
Xi’an University of Science and Technology, Department of Mechanics, Xi’an, 710054, China
Xinjiang Coking Coal Group Corporat ion Limited, Xinjiang 830025, China

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