Mechanisms underlying coal instability during coal and gas outbursts induced by deep mining

Authors

• ZHANG Chaolin, Key Laboratory of Gas and Fire Control for Coal Mines, Ministry of Education, Xuzhou 221116, China; State Key Laboratory of Coal Mine Disaster Prevention and Control, Xuzhou 221116, China; School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, ChinaFollow
• LI Yunfu, Key Laboratory of Gas and Fire Control for Coal Mines, Ministry of Education, Xuzhou 221116, China; State Key Laboratory of Coal Mine Disaster Prevention and Control, Xuzhou 221116, China; School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China
• LI Zhonghui, Key Laboratory of Gas and Fire Control for Coal Mines, Ministry of Education, Xuzhou 221116, China; State Key Laboratory of Coal Mine Disaster Prevention and Control, Xuzhou 221116, China; School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China
• WANG Enyuan, Key Laboratory of Gas and Fire Control for Coal Mines, Ministry of Education, Xuzhou 221116, China; State Key Laboratory of Coal Mine Disaster Prevention and Control, Xuzhou 221116, China; School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China; Jiangsu Safety Emergency Equipment Technology Innovation Center, Xuzhou 221116, China
• YANG Shiji, Key Laboratory of Gas and Fire Control for Coal Mines, Ministry of Education, Xuzhou 221116, China; State Key Laboratory of Coal Mine Disaster Prevention and Control, Xuzhou 221116, China; School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China
• CHEN Jiawei, Key Laboratory of Gas and Fire Control for Coal Mines, Ministry of Education, Xuzhou 221116, China; State Key Laboratory of Coal Mine Disaster Prevention and Control, Xuzhou 221116, China; School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China
• WANG Meng, Jiangsu Safety Emergency Equipment Technology Innovation Center, Xuzhou 221116, China

Abstract

Objective The gradual depletion of shallow coal resources drives a shift to the mining of deep coal seams. However, the complex deep mining environment significantly increases the potential risks and severity of coal and gas outbursts. Therefore, there exists an urgent need to investigate the mechanisms underlying the mechanical instability of coals under deep mining, aiming to provide guidance for the safe mining of deep coal mines.Methods By integrating physical experiments, numerical simulations, and theoretical analysis, this study investigated coal and gas outbursts under burial depths of 500 m, 1000 m, and 1600 m and established a multi-field coupling model that incorporates the coal deformation, gas flow, and coal damage fields. Furthermore, it revealed the mechanisms underlying the mechanical instability of coals during coal and gas outbursts under deep mining.Results and Conclusions Physical experiment results indicate that during coal and gas outbursts, the coal seams exhibited a rise in the pressure relief rate as the burial depth increased, with the relative outburst intensity increasing to 29.05%, 38.05%, and 42.70% under burial depths of 500 m, 1000 m, and 1600 m, respectively. The post-outburst temperature of the coal seams was found to decrease significantly as the burial depth increased, with the maximum temperature drops reaching 0.17 ℃, 0.37 ℃, and 0.55 ℃ under burial depths of 500 m,1000 m, and 1600 m, respectively. During coal and gas outbursts, the migration velocity of pulverized coals was observed to increase with the burial depth, reaching peaks of up to 22.08 m/s, 22.87 m/s, and 26.58 m/s under burial depths of 500 m, 1000 m, and 1600 m, respectively. Overall, a greater burial depth corresponded to a stronger outburst dynamic. Numerical simulation results reveal that with decreasing lateral pressure coefficient and increasing gas pressure during coal and gas outbursts, the coal damage zone evolved from a semicircular shape to a butterfly shape while propagating primarily in the vertical direction. The deflection angles of the damage cavity increased to 8.1°, 19.0°, and 34.4° under burial depths of 500 m, 1000 m, and 1600 m, respectively. Under the latter two burial depths, the maximum permeability occurred at the exposed surface of coals, reaching 10.8 times and 47.5 times the initial permeability, respectively. The maximum seepage force was also identified at the exposed surface, reaching up to 3.62 MPa/m, 7.74 MPa/m, and 11.93 MPa/m under burial depths of 500 m, 1000 m, and 1600 m, respectively. Based on the variation characteristics of vertical stress, permeability, and seepage force during the transition from moderately deep to ultra-deep mining, the coal seams can be divided into a rapid change zone, a fluctuation zone, and a stable zone. Under deep mining, the coals were subjected to high in-situ stress and high gas pressure, manifested as high vertical stress and high seepage force, respectively, which led to coal failure, an expanded plastic zone, and significantly elevated outburst risks. Further theoretical analysis of the mechanical properties of deep coals demonstrates that the coal and gas outbursts experienced four mechanical evolution stages: preparation, initiation, development, and termination. The analytical results systematically reveal that the mechanical instability of deep coals was jointly governed by high in-situ stress and high seepage force. This finding provides a new theoretical perspective for the mechanical evolution process of deep coal and gas outbursts. Given the damage characteristics of deep coals, along with the high seepage force in their fluctuation zones, it is necessary to implement intensified measures to enhance pressure relief and permeability in the prevention engineering of coal seam and gas outbursts at depth. These efforts will help break the coupling between the in-situ stress concentration and high gas pressure accumulation and reduce the energy that induces deep coal and gas outbursts in fluctuation zones.

Keywords

coal and gas outburst, mechanism of coal instability, deep mining, coal damage, deflection angle of a damage cavity, seepage force

DOI

10.12363/issn.1001-1986.25.12.0888

Recommended Citation

ZHANG Chaolin, LI Yunfu, LI Zhonghui, et al. (2026) "Mechanisms underlying coal instability during coal and gas outbursts induced by deep mining," Coal Geology & Exploration: Vol. 54: Iss. 5, Article 8.
DOI: 10.12363/issn.1001-1986.25.12.0888
Available at: https://cge.researchcommons.org/journal/vol54/iss5/8

Reference

[1] DING Yunna,LI Bobo,LI Jianhua,et al. A mini–review on coal permeability under combined thermal and mechanical effects[J]. Energy & Fuels,2025,39(45):21659−21676.

[2] 张超林,王培仲,王恩元,等. 我国煤与瓦斯突出机理70年发展历程与展望[J]. 煤田地质与勘探,2023,51(2):59−94

ZHANG Chaolin,WANG Peizhong,WANG Enyuan,et al. Coal and gas outburst mechanism:Research progress and prospect in China over the past 70 years[J]. Coal Geology & Exploration,2023,51(2):59−94

[3] 刘高峰,李宝林,张震,等. 不同变质煤的瓦斯膨胀能演化特征及其突出预测启示[J]. 煤田地质与勘探,2023,51(10):1−8

LIU Gaofeng,LI Baolin,ZHANG Zhen,et al. Gas expansion energy of coals with different metamorphic degrees:Evolutionary characteristics and their implications for the outburst prediction[J]. Coal Geology & Exploration,2023,51(10):1−8

[4] 王勃,徐凤银,刘文革,等. 煤矿瓦斯动力灾害地面治理关键技术与应用[J]. 煤田地质与勘探,2025,53(4):30−45

WANG Bo,XU Fengyin,LIU Wenge,et al. Key technologies for surface control of gas dynamic disasters in coal mines and their application[J]. Coal Geology & Exploration,2025,53(4):30−45

[5] 曹运兴,张海洋,张震,等. 正断层上盘煤与瓦斯突出特征与地应力场控制机理[J]. 煤田地质与勘探,2022,50(4):61−69

CAO Yunxing,ZHANG Haiyang,ZHANG Zhen,et al. Characteristics of coal and gas outburst and controlling mechanism of stress field in the hanging wall of normal faults[J]. Coal Geology & Exploration,2022,50(4):61−69

[6] 张超林,刘明亮,王恩元,等. 煤层渗透性对煤与瓦斯突出的影响规律及控制机理[J]. 煤炭学报,2024,49(12):4842−4854

ZHANG Chaolin,LIU Mingliang,WANG Enyuan,et al. Influence law and control mechanism of coal seam permeability on coal and gas outburst[J]. Journal of China Coal Society,2024,49(12):4842−4854

[7] 张超林,王奕博,王恩元,等. 煤与瓦斯突出煤粉在巷道内运移分布规律试验研究[J]. 煤田地质与勘探,2022,50(6):11−19

ZHANG Chaolin,WANG Yibo,WANG Enyuan,et al. Experimental study on the migration and distribution law of pulverized coal in roadway during coal and gas outburst[J]. Coal Geology & Exploration,2022,50(6):11−19

[8] 蒋静宇,董晓斌,魏民涛,等. 构造异常区能量单元切割理论及冲孔–爆破协同增透技术[J]. 煤炭学报,2025,50(5):2477−2495

JIANG Jingyu,DONG Xiaobin,WEI Mintao,et al. Study and application of the energy unit cutting theory and punching–blasting synergy permeability enhancement technology in tectonic anomaly areas of coal mines[J]. Journal of China Coal Society,2025,50(5):2477−2495

[9] 程远平,雷杨,杨斯杰. 煤与瓦斯突出相似模拟试验的能量原理[J]. 煤炭学报,2023,48(11):4078−4096

CHENG Yuanping,LEI Yang,YANG Sijie. Energy principle of simulation experiments on coal and gas outburst[J]. Journal of China Coal Society,2023,48(11):4078−4096

[10] (苏)B. B. 霍多特. 煤与瓦斯突出[M]. 宋士钊，王佑安，译. 北京：中国工业出版社，1966.

[11] 氏平增之. 煤与瓦斯突出机理的模型研究及其理论探讨：第21届国际煤矿安全研究会议，1985[C].

[12] 邓全封,栾永祥,王佑安. 煤与瓦斯突出模拟试验[J]. 煤矿安全,1989,20(11):5−10

[13] 蒋承林,俞启香. 煤与瓦斯突出机理的球壳失稳假说[J]. 煤矿安全,1995,26(2):17−25

[14] 胡千庭,周世宁,周心权. 煤与瓦斯突出过程的力学作用机理[J]. 煤炭学报,2008,33(12):1368−1372

HU Qianting,ZHOU Shining,ZHOU Xinquan. Mechanical mechanism of coal and gas outburst process[J]. Journal of China Coal Society,2008,33(12):1368−1372

[15] 许江,陶云奇,尹光志,等. 煤与瓦斯突出模拟试验台的改进及应用[J]. 岩石力学与工程学报,2009,28(9):1804−1809

XU Jiang,TAO Yunqi,YIN Guangzhi,et al. Amelioration and application of coal and gas outburst simulation experiment device[J]. Chinese Journal of Rock Mechanics and Engineering,2009,28(9):1804−1809

[16] 郭怀广,朱立凯. 深部动力灾害诱发机理及影响因素研究[J]. 煤炭科学技术,2021,49(5):175−181

GUO Huaiguang,ZHU Likai. Discussion on mechanism and influencing factors of deep dynamic disaster[J]. Coal Science and Technology,2021,49(5):175−181

[17] 周中立,张帅,杨胜强,等. 突出煤层沿空掘巷卸压应力降低区宽度研究[J]. 矿业安全与环保,2023,50(2):97−102

ZHOU Zhongli,ZHANG Shuai,YANG Shengqiang,et al. Study on the width of stress-relaxed area for pressure-relief of outburst coal seam in gob-side entry driving[J]. Mining Safety & Environmental Protection,2023,50(2):97−102

[18] 唐巨鹏,黄文哲,潘一山,等. 掘进工作面逼近构造煤区激发煤与瓦斯突出机制试验研究[J]. 岩石力学与工程学报,2025,44(12):3170−3183

TANG Jupeng,HUANG Wenzhe,PAN Yishan,et al. Mechanism of coal and gas outburst induced by excavation working face approaching tectonic coal area[J]. Chinese Journal of Rock Mechanics and Engineering,2025,44(12):3170−3183

[19] 舒龙勇,闫振东,刘正帅,等. 受载煤体多参量随钻监测试验与随钻突出预测方法[J]. 煤炭学报,2025,50(10):4774−4790

SHU Longyong,YAN Zhendong,LIU Zhengshuai,et al. Multi–parameter while–drilling monitoring experiment of loaded coal and while–drilling outburst prediction method[J]. Journal of China Coal Society,2025,50(10):4774−4790

[20] ZHAO Yang,LIN Baiquan,LIU Ting,et al. Mechanism of multifield coupling–induced outburst in mining–disturbed coal seam[J]. Fuel,2020,272:117716.

[21] 张士岭,崔俊飞,和树栋. 煤与瓦斯突出过程中渗流与煤岩体破坏耦合作用机制[J]. 煤炭科学技术,2024,52(12):105−115

ZHANG Shiling,CUI Junfei,HE Shudong. Coupling mechanism of seepage and coal and rock mass destruction during coal and gas outburst[J]. Coal Science and Technology,2024,52(12):105−115

[22] XU Chao,MA Sibo,WANG Kai,et al. Stress and permeability evolution of high–gassy coal seams for repeated mining[J]. Energy,2023,284:128601.

[23] 李峰,王琛琛,王博,等. 基于多区组合煤体的煤与瓦斯突出动力学机制[J]. 煤田地质与勘探,2024,52(5):12−24

LI Feng,WANG Chenchen,WANG Bo,et al. Dynamic mechanisms of coal and gas outbursts based on a multi–zone combined coal model[J]. Coal Geology & Exploration,2024,52(5):12−24

[24] 涂庆毅,孙浩宇,袁亮,等. 突出过程瓦斯急速解吸诱发颗粒煤二次破碎理论与试验研究[J]. 中国矿业大学学报,2025,54(4):825−836

TU Qingyi,SUN Haoyu,YUAN Liang,et al. Theoretical and experimental study on secondary crushing induced by rapid desorption of coal particle gas during coal and gas outburst process[J]. Journal of China University of Mining & Technology,2025,54(4):825−836

[25] 冀瑞锋. 不均匀应力场下含瓦斯煤层开挖巷道破坏规律数值模拟研究[J]. 煤炭技术,2025,44(8):205−209

JI Ruifeng. Numerical simulation study on failure mechanisms of excavated roadways in gas–containing coal seams under non–uniform stress fields[J]. Coal Technology,2025,44(8):205−209

[26] 杜锋,崔伟龙,马骥,等. 机械振动下含瓦斯煤人工声学信号频谱响应特征研究[J]. 采矿与岩层控制工程学报,2026,8(1):013024

DU Feng,CUI Weilong,MA Ji,et al. Study on spectral response characteristics of artificial acoustic signals of gas–bearing coal under mechanical vibration[J]. Journal of Mining and Strata Control Engineering,2026,8(1):013024

[27] 李新平,汪斌,周桂龙. 我国大陆实测深部地应力分布规律研究[J]. 岩石力学与工程学报,2012,31(增刊1):2875−2880

LI Xinping,WANG Bin,ZHOU Guilong. Research on distribution rule of geostress in deep stratum in Chinese mainland[J]. Chinese Journal of Rock Mechanics and Engineering,2012,31(Sup.1):2875−2880

[28] 张超林,王恩元,王奕博,等. 多功能煤与瓦斯突出模拟试验系统研制与应用[J]. 岩石力学与工程学报,2022,41(5):995−1007

ZHANG Chaolin,WANG Enyuan,WANG Yibo,et al. Development and application of multi–functional test system for coal and gas outburst simulation[J]. Chinese Journal of Rock Mechanics and Engineering,2022,41(5):995−1007

[29] 曹偈,胡千庭,赵旭生,等. 碎煤初期解吸瓦斯对煤与瓦斯突出动力效应影响的试验研究[J]. 煤炭学报,2025,50(9):4260−4276

CAO Jie,HU Qianting,ZHAO Xusheng,et al. Experimental study on the influence of initial desorbed gas from crushed coal on the dynamic effects of coal and gas outburst[J]. Journal of China Coal Society,2025,50(9):4260−4276

[30] 周斌,杨兆龙,李树刚,等. 真三维应力状态下不同地应力条件对煤与瓦斯突出两相流动力学特征的影响[J]. 中国矿业大学学报,2025,54(5):1053−1065

ZHOU Bin,YANG Zhaolong,LI Shugang,et al. Effects of different geo–stress on two–phase flow dynamics of coal–gas outbursts in true triaxial stress state[J]. Journal of China University of Mining & Technology,2025,54(5):1053−1065

[31] 程亮. 巷道布置方式影响下突出煤–瓦斯两相流动力学行为及其致灾机制研究[D]. 重庆：重庆大学，2024.

CHENG Liang. Study on the dynamic behavior of outburst coal–gas two–phase flow and its disaster–causing mechanism under the influence of roadway layout[D]. Chongqing：Chongqing University，2024.

[32] LI Yunfu,ZHANG Chaolin,WANG Enyuan,et al. Mechanism of energy instability release during coal and gas outburst[J]. Fuel,2025,401:135961.

[33] 王登科,唐家豪,魏建平,等. 煤层瓦斯多机制流固耦合模型与瓦斯抽采数值模拟分析[J]. 煤炭学报,2023,48(2):763−775

WANG Dengke,TANG Jiahao,WEI Jianping,et al. A fluid–solid coupling model of coal seam gas considering gas multi–mechanism flow and a numerical simulation analysis of gas drainage[J]. Journal of China Coal Society,2023,48(2):763−775

[34] LI Yunfu,ZHANG Chaolin,LI Bobo,et al. Tensile failure mechanism enhanced by uncovering coal area during coal and gas outburst[J]. International Journal of Mining Science and Technology,2025,35(12):2231−2243.

[35] DETOURNAY E，CHENG A H D. Fundamentals of poroelasticity[M]//FAIRHURST C. Analysis and design methods. Amsterdam：Elsevier，1993：113–171.

[36] ZHOU H W,ZHAO J W,SU T,et al. Characterization of gas flow in backfill mining–induced coal seam using a fractional derivative–based permeability model[J]. International Journal of Rock Mechanics and Mining Sciences,2021,138:104571.

[37] SOLEIMANI F,SI Guangyao,ROSHAN H,et al. Numerical modelling of coal and gas outburst initiation using energy balance principles[J]. Fuel,2023,334:126687.

[38] ZHENG Chunshan,KIZIL M S,CHEN Zhongwei,et al. Role of multi–seam interaction on gas drainage engineering design for mining safety and environmental benefits:Linking coal damage to permeability variation[J]. Process Safety and Environmental Protection,2018,114:310−322.

[39] MORA C A,WATTENBARGER R A. Analysis and verification of dual porosity and CBM shape factors[J]. Journal of Canadian Petroleum Technology,2009,48(2):17−21.

[40] ZHAO Yang,LIN Baiquan,LIU Ting,et al. Flow field evolution during gas depletion considering creep deformation[J]. Journal of Natural Gas Science and Engineering,2019,65:45−55.

[41] 康红普,伊丙鼎,高富强,等. 中国煤矿井下地应力数据库及地应力分布规律[J]. 煤炭学报,2019,44(1):23−33

KANG Hongpu,YI Bingding,GAO Fuqiang,et al. Database and characteristics of underground in–situ stress distribution in Chinese coal mines[J]. Journal of China Coal Society,2019,44(1):23−33

[42] TU Qingyi,CHENG Yuanping,LIU Qingquan,et al. Investigation of the formation mechanism of coal spallation through the cross–coupling relations of multiple physical processes[J]. International Journal of Rock Mechanics and Mining Sciences,2018,105:133−144.

[43] LU Shouqing,WANG Chengfeng,LIU Qingquan,et al. Numerical assessment of the energy instability of gas outburst of deformed and normal coal combinations during mining[J]. Process Safety and Environmental Protection,2019,132:351−366.

[44] 蔚默然,王开,张小强,等. 超临界CO₂作用下不同高度比煤岩组合体力学特性及能量演化规律[J]. 矿业安全与环保,2025,52(1):134−141

YU Moran,WANG Kai,ZHANG Xiaoqiang,et al. Mechanical properties and energy evolution of coal-rock assemblages with different height ratios under supercritical CO₂ action[J]. Mining Safety & Environmental Protection,2025,52(1):134−141

[45] 谢和平,高峰,鞠杨,等. 深部开采的定量界定与分析[J]. 煤炭学报,2015,40(1):1−10

XIE Heping,GAO Feng,JU Yang,et al. Quantitative definition and investigation of deep mining[J]. Journal of China Coal Society,2015,40(1):1−10