Evolutionary characteristics and fine-scale zoning of overburden fractures for pressure-relief mining of soft coal seams

Authors

• WANG Long, College of Environment and Resources, Xiangtan University, Xiangtan 411105, ChinaFollow
• DENG Zhiliang, School of Energy and Mining Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
• ZHANG Zongxiang, College of Environment and Resources, Xiangtan University, Xiangtan 411105, China
• GUO Baohua, School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo 454003, China
• TAN Hongchen, College of Environment and Resources, Xiangtan University, Xiangtan 411105, China
• ZHAO Pengtao, Hunan Gas Control and Utilization Engineering Research Center Co., Ltd., Changsha 410004, China
• HU Longsheng, Hunan Gas Control and Utilization Engineering Research Center Co., Ltd., Changsha 410004, China

Abstract

Objective During the mining of coal seam groups, substantial gas is prone to rush into the mining face from adjacent coal seams through interconnected mining-induced fractures. This poses a threat to safe coal mining. Under pressure-relief mining of soft coal seams, their low permeability and high stress sensitivity present challenges to the successive mining of protective and protected coal seams. Specifically, mechanisms behind the overburden fracture evolution remain poorly understood, and it is difficult to identify preferential pathways for gas migration accurately. Methods This study investigated coal seam groups in the Jiahe mining area of Hunan Province as the engineering background. Using physical simulations with similar materials and numerical simulations based on the 3DEC software, this study systematically examined overburden fracture evolution and stress distribution patterns during pressure-relief mining of the coal seam groups. Accordingly, a fine-scale zoning model tailored to soft coal seams was developed. Using this model, the layout of high-level boreholes for gas extraction was optimized. Results and Conclusions After the mining of coal seam VI as the lower protective layer, the overburden exhibited a caving zone height of 4.2 m and a fracture zone height of 23.6 m, providing initial fracture fields for the subsequent pressure-relief mining of protected coal seam Ⅴ. The overburden fractures of mining face 2152 of coal seam Ⅴ exhibited distinct multi-stage evolution. The height of cross-layer fractures increased with the advancement of the mining face, tending to stabilize after the advancing distance reached 37.6 m. In contrast, delamination fractures kept propagating upward, with an ultimate height of up to approximately 55 m. Ultimately, an O-shaped fracture circle that penetrated the fracture and caving zones was formed in the overburden. Physical simulations with similar materials and numerical simulations yielded consistent results, with the caving zone height of coal seam V estimated at 8.5 m and 7.2 m and the fracture zone height of the coal seam determined at 37.6 m and 38.4 m, respectively. Meanwhile, physical and numerical simulations revealed that stress concentration zones formed by re-compaction occurred near advancing distances ranging from 35 m to 36 m and from 96 m to 100 m, respectively. The fracture evolution patterns indicate that the fracture zone in the conventional vertical three zones can be further subdivided into a cross-layer fracture zone and a pressure-relief fracture zone. Furthermore, using delamination rates and breaking angles as quantitative boundaries, horizontal four zones were reconstructed: a coal wall disturbance zone, a detachment layer development zone, a voussoir beam structure zone, and a goaf compaction zone. Among these, the voussoir beam structure zone contained preferential pathways for gas migration. Field gas extraction using four sets of high-level boreholes demonstrates that boreholes with final holes arranged in the central part of the cross-layer fracture zone (distance from the roof: 25 m) outperformed in gas extraction, with a gas volume fraction of 86.4% and a pure gas flow rate of 2.62 m³/min. These results corroborate that the zoning model developed in this study can provide key parameters for the optimal horizon selection and regional targeted layout of high-level boreholes under pressure-relief mining of soft coal seams.

Keywords

soft coal seam, pressure-relief mining, overburden fracture, evolutionary pattern, zoning characteristics, high-level borehole

DOI

10.12363/issn.1001-1986.26.01.0069

Recommended Citation

WANG Long, DENG Zhiliang, ZHANG Zongxiang, et al. (2026) "Evolutionary characteristics and fine-scale zoning of overburden fractures for pressure-relief mining of soft coal seams," Coal Geology & Exploration: Vol. 54: Iss. 8, Article 7.
DOI: 10.12363/issn.1001-1986.26.01.0069
Available at: https://cge.researchcommons.org/journal/vol54/iss8/7

Reference

[1] 马宏宇,王遥,徐东方,等. 湘能集团瓦斯治理模式及展望[J]. 煤炭技术,2025,44(9):174−178 MA Hongyu,WANG Yao,XU Dongfang,et al. Gas management model and prospect of Hunan energy group[J]. Coal Technology,2025,44(9):174−178

[2] 赵鹏涛,王海桥,王龙,等. 非凝材料恒压注浆技术在松软煤层封孔中的应用[J]. 湖南科技大学学报(自然科学版),2024,39(2):9−16 ZHAO Pengtao,WANG Haiqiao,WANG Long,et al. Application of constant pressure grouting with non–condensable material to soft coalbed sealing[J]. Journal of Hunan University of Science and Technology (Natural Science Edition),2024,39(2):9−16

[3] 王恩元,张国锐,张超林,等. 我国煤与瓦斯突出防治理论技术研究进展与展望[J]. 煤炭学报,2022,47(1):297−322 WANG Enyuan,ZHANG Guorui,ZHANG Chaolin,et al. Research progress and prospect on theory and technology for coal and gas outburst control and protection in China[J]. Journal of China Coal Society,2022,47(1):297−322

[4] 肖正辉,邵龙义,鲁静,等. 湖南煤层气资源及其分布特征[J]. 中国煤炭地质,2010,22(3):17−20 XIAO Zhenghui,SHAO Longyi,LU Jing,et al. CBM resources and distribution characteristics in Hunan Province[J]. Coal Geology of China,2010,22(3):17−20

[5] 程志恒,陈亮,苏士龙,等. 近距离煤层群井上下联合防突模式及其效果动态评价[J]. 煤炭学报,2020,45(5):1635−1647 CHENG Zhiheng,CHEN Liang,SU Shilong,et al. Outburst prevention mode of ground and underground technology joint and its dynamic evaluation in contiguous coal seams[J]. Journal of China Coal Society,2020,45(5):1635−1647

[6] 刘泽功,袁亮,戴广龙,等. 开采煤层顶板环形裂隙圈内走向长钻孔法抽放瓦斯研究[J]. 中国工程科学,2004,6(5):32−38 LIU Zegong,YUAN Liang,DAI Guanglong,et al. Study on coal seam roof gas drainage from the strike of annular fracture areas by the long drill method[J]. Strategic Study of CAE,2004,6(5):32−38

[7] 杨科,刘帅. 深部远距离下保护层开采多关键层运移–裂隙演化–瓦斯涌出动态规律研究[J]. 采矿与安全工程学报,2020,37(5):991−1000 YANG Ke,LIU Shuai. Rule of multi–key strata movement–fracture evolution–dynamics of gas emission in deep long distance lower protective layer mining[J]. Journal of Mining and Safety Engineering,2020,37(5):991−1000

[8] 孙宝强,龚选平,范晓刚,等. 深部强采动工作面卸压瓦斯全生命周期分阶段精准治理方法[J]. 工矿自动化,2026,52(1):10−20 SUN Baoqiang,GONG Xuanping,FAN Xiaogang,et al. Precise staged control method for pressure–relief gas over full lifecycle of deep high–intensity mining working face[J]. Journal of Mine Automation,2026,52(1):10−20

[9] 袁亮. 卸压开采抽采瓦斯理论及煤与瓦斯共采技术体系[J]. 煤炭学报,2009,34(1):1−8 YUAN Liang. Theory of pressure–relieved gas extraction and technique system of integrated coal production and gas extraction[J]. Journal of China Coal Society,2009,34(1):1−8

[10] 程远平,付建华,俞启香. 中国煤矿瓦斯抽采技术的发展[J]. 采矿与安全工程学报,2009,26(2):127−139 CHENG Yuanping,FU Jianhua,YU Qixiang. Development of gas extraction technology in coal mines of China[J]. Journal of Mining & Safety Engineering,2009,26(2):127−139

[11] 柴敬,刘永亮,王梓旭,等. 保护层开采下伏煤岩卸压效应及其光纤监测[J]. 煤炭学报,2022,47(8):2896−2906 CHAI Jing,LIU Yongliang,WANG Zixu,et al. Pressure relief effect of protective layer mining and its optical fiber monitoring[J]. Journal of China Coal Society,2022,47(8):2896−2906

[12] 杨科,刘帅,唐春安,等. 多关键层跨煤组远程被保护层煤壁片帮机理及防治[J]. 煤炭学报,2019,44(9):2611−2621 YANG Ke,LIU Shuai,TANG Chun’an,et al. Mechanism and prevention of coal seam rib spalling in remote protected layer across coal group[J]. Journal of China Coal Society,2019,44(9):2611−2621

[13] 薛俊华,肖健,杜轩宏,等. 我国煤矿保护层开采卸压瓦斯抽采现状及发展趋势[J]. 煤田地质与勘探,2023,51(6):50−61 XUE Junhua,XIAO Jian,DU Xuanhong,et al. Current situation and development trend of pressure–relief gas extraction in the protective layer mining in coal mines in China[J]. Coal Geology & Exploration,2023,51(6):50−61

[14] 隋微波,温长云,孙文常,等. 水力压裂分布式光纤传感联合监测技术研究进展[J]. 天然气工业,2023,43(2):87−103 SUI Weibo,WEN Changyun,SUN Wenchang,et al. Joint application of distributed optical fiber sensing technologies for hydraulic fracturing monitoring[J]. Natural Gas Industry,2023,43(2):87−103

[15] 张超,孙莹洁,张发旺. 降雨诱发浅埋煤层采动滑坡成因机理及数值模拟[J]. 现代地质,2026,40(2):522−530 ZHANG Chao,SUN Yingjie,ZHANG Fawang. Mechanism and numerical simulation of shallow buried coal seam mining landslide induced by rainfall[J]. Geoscience,2026,40(2):522−530

[16] QIN Zongyi，YUAN Liang，GUO Hua，et al. Investigation of longwall goaf gas flows and borehole drainage performance by CFD simulation[J]. International Journal of Coal Geology，2015，150/151：51–63.

[17] HU Guozhong,XU Jialin,REN Ting,et al. Adjacent seam pressure–relief gas drainage technique based on ground movement for initial mining phase of longwall face[J]. International Journal of Rock Mechanics and Mining Sciences,2015,77:237−245.

[18] CAO Jie,LI Wenpu. Numerical simulation of gas migration into mining–induced fracture network in the goaf[J]. International Journal of Mining Science and Technology,2017,27(4):681−685.

[19] 司俊鸿,程根银,朱建芳,等. 采空区非均质多孔介质渗透特性三维建模及应用[J]. 煤炭科学技术,2019,47(5):220−224 SI Junhong,CHENG Genyin,ZHU Jianfang,et al. Three–dimensional modeling and application of permeability characteristics of heterogeneous porous media in goaf[J]. Coal Science and Technology,2019,47(5):220−224

[20] 张村,屠世浩,赵毅鑫,等. 基于渗流实验的三轴流固耦合离散元数值模拟研究[J]. 矿业科学学报,2019,4(1):23−33 ZHANG Cun,TU Shihao,ZHAO Yixin,et al. Discrete element numerical simulation of triaxial fluid solid coupling based on seepage experiment[J]. Journal of Mining Science and Technology,2019,4(1):23−33

[21] ZHANG Cun,LIU Jinbao,ZHAO Yixin,et al. Numerical simulation of broken coal strength influence on compaction characteristics in goaf[J]. Natural Resources Research,2020,29(4):2495−2511.

[22] 刘钦节,杨友兴,吴犇牛,等. 废弃矿井煤层气运移通道空间分布及抽采靶区优选[J]. 煤田地质与勘探,2025,53(8):76−86 LIU Qinjie,YANG Youxing,WU Benniu,et al. Spatial distribution of coalbed methane migration pathways and selection of optimal target areas for coalbed methane extraction for abandoned mines[J]. Coal Geology & Exploration,2025,53(8):76−86

[23] 赵鹏翔,郭旭,王超,等. 综采工作面采高影响瓦斯运–储区交叉融合机理[J]. 煤田地质与勘探,2025,53(8):31−41 ZHAO Pengxiang,GUO Xu,WANG Chao,et al. Mechanisms behind the cross and fusion of gas migration and storage zones under the influence of the mining height of fully mechanized mining faces[J]. Coal Geology & Exploration,2025,53(8):31−41

[24] 赵鹏翔,卓日升,李树刚,等. 采动覆岩卸压瓦斯运储通道属性参数拓扑关系研究[J]. 煤炭科学技术,2024,52(2):135−149 ZHAO Pengxiang,ZHUO Risheng,LI Shugang,et al. Research on the evolution mechanism of the topological relationship of the property parameters of the mining overburden rock pressure relief gas migration channel[J]. Coal Science and Technology,2024,52(2):135−149

[25] 王正帅,罗帅. 煤层群赋存条件下特厚煤层分层综放面瓦斯涌出量预测[J]. 煤炭科技,2025,46(5):146−150 WANG Zhengshuai,LUO Shuai. Prediction of gas emission from fully–mechanized caving face in extra–thick coal seam under the occurrence of coal seam group[J]. Coal Science & Technology Magazine,2025,46(5):146−150

[26] SINGH K K,SINGH D N,RANJITH P G. Laboratory simulation of flow through single fractured granite[J]. Rock Mechanics and Rock Engineering,2015,48(3):987−1000.

[27] ZHANG Cun,LIU Jinbao,ZHAO Yixin,et al. A fluid–solid coupling method for the simulation of gas transport in porous coal and rock media[J]. Energy Science & Engineering,2019,7(5):1913−1924.

[28] 汪北方,吕元昊,张晶. 浅埋复合采空区覆岩采动裂隙分区特征及其治理技术[J]. 煤炭科学技术,2025,53(2):41−52 WANG Beifang,LYU Yuanhao,ZHANG Jing. Zone feature and control technology of overlying strata mining–induced fracture in shallow buried compound goaf[J]. Coal Science and Technology,2025,53(2):41−52

[29] 陈歌,孙亚军,隋旺华,等. 我国煤矿区矿井水深井回灌的研究现状和技术挑战[J]. 工程地质学报,2025,33(3):1043−1057 CHEN Ge,SUN Yajun,SUI Wanghua,et al. Technological challenge and research status of mine water deep re–injection in coal mining areas of China[J]. Journal of Engineering Geology,2025,33(3):1043−1057

[30] 孔祥国,张辉,李树刚,等. 基于裂隙场和渗流场融合判识的覆岩分区演化特征及采厚效应[J]. 中国矿业大学学报,2026,55(1):164−179 KONG Xiangguo,ZHANG Hui,LI Shugang,et al. Zonal evolution characteristics of overlying strata and mining thickness effect based on integrated identification of fracture field and seepage field[J]. Journal of China University of Mining and Technology,2026,55(1):164−179

[31] 孔祥国,赵天烁,林海飞,等. 特厚煤层覆岩裂隙–渗流区域演化规律及工程应用[J]. 煤田地质与勘探,2025,53(1):102−113 KONG Xiangguo,ZHAO Tianshuo,LIN Haifei,et al. Fracture–seepage characteristic zones of the overburden of extra–thick coal seams:Evolutionary patterns and their engineering applications[J]. Coal Geology & Exploration,2025,53(1):102−113

[32] 杨伟强,郭文兵,赵高博,等. 基于岩层挠曲变形的“竖三带”理论判别方法及工程应用[J]. 煤炭科学技术,2022,50(10):42−50 YANG Weiqiang,GUO Wenbing,ZHAO Gaobo,et al. Theoretical judgement method of overburden “three–zone” based on rock strata deflection deformation and its engineering application[J]. Coal Science and Technology,2022,50(10):42−50

[33] 陶雪峰,石必明,华心祝,等. 废弃矿井采空区基本顶破断机理及裂隙分布规律[J]. 煤田地质与勘探,2025,53(11):99−112 TAO Xuefeng,SHI Biming,HUA Xinzhu,et al. Fracture mechanisms and fracture distribution patterns of main roofs in goaves within abandoned mines[J]. Coal Geology & Exploration,2025,53(11):99−112

[34] 郭明杰,郭文兵,赵高博,等. 长壁开采覆岩内水平定向长钻孔位置特征与卸压瓦斯抽采机理[J]. 煤炭学报,2023,48(10):3750−3765 GUO Mingjie,GUO Wenbing,ZHAO Gaobo,et al. Position characteristics of horizontal–directional long boreholes in overlying strata and drainage mechanism of pressure–relief gas in longwall mining[J]. Journal of China Coal Society,2023,48(10):3750−3765