深部煤层具有高瓦斯、低透气性特点，CO₂气爆作为煤层增透的有效手段之一，可显著提高瓦斯抽采效率，故探究CO₂气爆的作用机理，能够指导该方法在保障安全生产的前提下最大限度的提升经济效益。本文基于弹性力学与断裂力学，构建CO₂气爆煤岩体裂纹扩展力学模型，描述了应力波强弱与裂纹扩展迹长的关系，说明了爆生气体的能量加持作用。不含空孔煤岩体受到CO₂气体冲击时，煤岩体爆孔孔周在应力波作用下，于边界处产生四周均布的拉应力载荷，致使煤层自中心处环向开裂。爆生气体在吸收冲击波能量后发生膨胀并释放一定的能量，对应力波产生协同作用，促使煤岩体爆孔孔周裂纹得到充分发展。考虑到自由面对裂纹扩展的影响，引入空孔效应，分别开展了不含空孔与含空孔试样的CO₂气爆物理试验。利用光学非接触式应变测量系统(VIC-3D)观测试样表面位移变化，分析煤岩体爆孔孔周裂纹扩展规律，并通过超声波监测系统收集爆破过程中的波幅，计算衰减系数以反映煤岩体内部损伤情况。

CO₂气爆过程中两次超声波波幅的出现并非偶然，其反映了爆生气体协同应力波促进裂纹扩展的实质性。应力大小可以反映应力波与爆生气体协同作用的强弱，应力越大，协同作用越强，裂纹扩展越充分。应力与衰减系数在峰值时间段的重合现象，说明该时间段应力波与爆生气体的协同作用最强。对角线方向上应力强度因子的水平分量与竖直分量基本持平且试样的裂纹扩展最深，说明水平分量与竖直分量越接近煤岩体越容易开裂。自由面的增加诱发了空孔效应，CO₂气爆过程中压缩波与反射波迭加产生径向拉应力，突破煤岩体抗压强度后，发生破碎，爆腔内压力逐渐达到峰值，在爆孔与空孔之间形成一条近似直线的主裂纹通道，对煤岩体裂纹扩展起导向作用。此时，应力与衰减系数均达到峰值，煤岩体内部损伤最为剧烈。

采用LS-DYNA软件，分别在不含空孔和含空孔条件下，模拟研究CO₂气爆后煤岩体爆孔孔周裂纹扩展规律，具象化反映空孔的导向性。数值模拟CO₂气爆下含空孔煤岩体裂纹扩展特征演变情况，发现0.13s主裂纹通道形成，0.18s煤岩体应力达到峰值且能量耗散最大。能量与应力的负相关关系与试验结果一致，表明CO₂气爆过程中，空孔效应为煤岩体裂纹扩展提供了良好的导向作用。本文将理论分析、试验探究及数值模拟有机结合，完善了CO₂气爆致裂的基础理论体系，阐明了爆生气体对应力波的协同作用，反映了空孔效应影响的煤岩体裂纹扩展特征规律，能够指导CO₂气爆技术安全高效的应用于煤矿生产现场，对进一步强化煤层增透效果、提高瓦斯抽采效率具有重要现实意义。

Deep coal seam has the characteristics of high gas and low permeability. As one of the effective means to increase the permeability of coal seam, CO₂ gas blasting can significantly improve the efficiency of gas drainage. Therefore, exploring the mechanism of CO₂ gas blasting can ensure the safety and economy of this method applied in coal mine production sites. Based on elastic mechanics and fracture mechanics, the crack propagation mechanical model of CO₂ gas blasting coal mass is constructed in this paper. The relationship between the stress wave intensity and the crack propagation trace length is described, and the energy addition effect of blasting gas is explained. When the coal and rock mass without void is impacted by CO₂ gas, the tensile stress load distributed around the boundary is produced under the action of stress wave, which causes the coal seam to crack in the circumferential direction from the center. After absorbing the energy of the shock wave, the blasting gas expands and releases a certain amount of energy, which produces a synergistic effect on the stress wave, which promotes the full development of cracks around the blasting hole in coal and rock mass. The void effect is introduced to consider the influence of freedom on crack propagation. The physical tests of CO₂ gas blasting with and without voids were carried out respectively. The surface displacement of the sample was observed by an optical non-contact strain measurement system (VIC-3D), and the law of crack propagation around the burst hole in coal and rock mass was analyzed. The amplitude in the blasting process is collected by the ultrasonic monitoring system, and the attenuation coefficient is calculated to reflect the internal damage of coal and rock mass.

The appearance of two ultrasonic amplitudes in the process of CO₂ gas blasting is not accidental, which reflects the substance of crack propagation promoted by the synergistic stress wave of detonating gas. The magnitude of stress can reflect the synergistic effect of stress waves and blasting gas. The greater the stress is, the stronger the synergistic effect is and the more sufficient the crack propagation is. The characteristic coincidence phenomenon of stress and attenuation coefficient in the peak period shows that the synergistic effect of stress wave and blasting gas is the strongest in this period. In the diagonal direction, the horizontal component of the stress intensity factor is basically the same as the vertical component, and the crack propagation of the specimen is the deepest, indicating that the closer the horizontal component is to the vertical component, the easier it is to crack. The void effect is induced by the increase of the free surface. In the process of CO₂ gas blasting, the superposition of compression wave and reflected wave produces radial tensile stress, which breaks through the compressive strength of rock mass. The pressure in the blasting cavity gradually reaches the peak, and an approximately straight line main crack channel is formed between the blasting hole and the empty hole. It plays a guiding role in the crack propagation of coal and rock mass. At this time, the stress and attenuation coefficient reach the peak, and the internal damage of coal and rock mass is the most severe.

Under the condition of no empty hole and empty hole, LS-DYNA software is used to simulate and study the law of crack propagation around the blasting hole in coal and rock mass after CO₂ gas blasting, which vividly reflects the orientation of the empty hole. The evolution of crack propagation characteristics of coal and rock mass with holes under CO₂ gas blasting is numerically simulated. It is found that the main crack channel is formed in 0.13s, the stress of coal and rock mass reaches the peak value and the energy dissipation reaches the maximum in 0.18s. The negative correlation between energy and stress is consistent with the experimental results, which show that the void effect provides good guidance for the crack propagation of coal seam in the process of CO₂ gas blasting. With the organic combination of theoretical analysis, experimental exploration, and numerical simulation, this paper improves the basic theoretical system of CO₂ gas blasting, expounds the synergistic effect of blasting gas on stress waves, and reflects the characteristic law of crack propagation in coal seam affected by void effect, which can guide the safe and efficient application of CO₂ gas blasting technology in coal mine production site, and has important practical significance to further strengthen the permeability enhancement effect of coal seam and improve the efficiency of gas extraction.

[1] 袁亮. 国深部煤与瓦斯共采战略思考[J]. 煤炭学报, 2016, 41(1): 1-6.

[2] 潘红宇, 葛迪, 张天军, 等. 应变率对岩石裂隙扩展规律的影响[J]. 煤炭学报, 2018, 43(03): 675-683.

[3] 潘红宇, 董晓刚, 张天军, 等. 单轴压缩下松软煤样破裂损伤演化特性研究[J]. 西安科技大学学报, 2018, 38(02): 202-209.

[4] T Chen, ZM Wang, G Yang, JJ Li, RJ Peng. The indoor experiment & analysis of CBM cavity completion to improve coal seam permeability [J]. International Journal of Earth Sciences & Engineering, 2013, 6(6): 1303-1310.

[5] 冯彦军, 康红普. 复合型裂纹水力压裂研究[J]. 煤炭学报, 2013, 38(2): 226-232.

[6] 王冕, 任倍良. 高突松软煤层水力冲孔快速揭煤应用[J]. 煤炭科学技术, 2015, 43(增): 96-98.

[7] Lu Tingkan, Zhao Zhijian, Hu Hefeng. Improving the gate road development rate and reducing outburst occurrences using the waterjet technique in high gas content outburst-prone soft coalseam[J]. International Journal of Rock Mechanics and Mining Sciences, 2011, 48(8): 1271-1282.

[8] 郭德勇, 商登莹, 吕鹏飞, 等. 深孔聚能爆破坚硬顶板弱化实验研究[J]. 煤炭学报, 2013, 38(7): 1149-1153.

[9] 高坤. 高能气体冲击煤体增透技术实验研究及应用[D]. 辽宁工程技术大学, 2013.

[10] 王兆丰, 孙小明, 陆庭侃, 等. 液态CO2相变致裂强化瓦斯预抽试验研究[J]. 河南理工大学学报(自然科学版), 2015(01): 1-5.

[11] 孙博. 煤体爆破裂隙扩展规律及其试验研究[D]. 河南理工大学, 2011.

[12] 李启月, 吴正宇, 黄武林. 直眼掏槽空孔效应的计算模型改进与分析[J]. 采矿与安全工程学报, 2018, 35(05): 925-930.

[13] 卢义玉, 廖引, 汤积仁, 等. 页岩超临界CO2压裂起裂压力与裂缝形态试验研究[J]. 煤炭学报, 2018, 43(01): 175-180.

[14] 刘健, 刘泽功, 石必明, 等. 突出煤层快速掘进深孔预裂爆破预抽瓦斯技术[J]. 煤炭科学技术, 2008, 36(8): 45-48.

[15] 刘健. 低透气煤层深孔预裂爆破增透技术研究及应用[D]. 安徽理工大学, 2008.

[16] 刘健, 刘泽功. 深孔预裂爆破技术在井筒揭煤中的应用研究[J]. 煤炭科学技术, 2012, 40(2): 19-24.

[17] 张帆, 马耕. 大尺寸真三轴煤岩水力压裂模拟试验与裂缝扩展分析[J]. 岩土力学, 2019, 40(05): 1890-1897.

[18] 袁亮, 刘业娇, 田志超, 等. 地面垂直钻孔预抽特厚煤层瓦斯数值试验与应用[J]. 岩土力学, 2019, 40(01): 370-378.

[19] 冯丹, 许江, 陶云奇, 等. 水力冲孔物理模拟试验系统研制及其应用[J]. 采矿与安全工程学报, 2017, 34(04): 782-788.

[20] 文虎, 李珍宝, 王振平, 等. 煤层注液态CO2压裂增透过程及裂纹扩展特征试验[J]. 煤炭学报, 2016, 41(11): 2793-2799.

[21] 黄文尧, 颜事龙, 刘泽功, 等. 煤矿瓦斯抽采水胶药柱在煤层深孔爆破中的研究与应用[J]. 煤炭学报, 2012, 37(3): 472-476.

[22] 王海东. 深部开采低渗透煤层预裂控制爆破增透机理研究[D]. 中国地震局工程地质研究所, 2012.

[23] 韩颖, 刘少飞. 深部煤层渗透性能主控因素研究进展及展望[J]. 煤矿安全, 2018, 49(04): 12-15.

[24] 蔡峰, 于鹏, 马衍坤, 等. 砂砾岩油气储层水力压裂强化增透裂隙扩展特性试验研究[J]. 岩土力学, 2019(06): 1-8.

[25] 蔡峰. 高瓦斯低透气性煤层深孔预裂爆破强化增透效应研究[D]. 安徽理工大学, 2009.

[26] Cai Feng, Liu Zegong. Intensified extracting gas and rapidly diminishing outburst risk using deep-hole presplitting blast technology before opening coal seam in shaft influenced by fault[C]. First International Symposium on Mine Safety Science and Engineering Procedia Engineering 26 (2011): 418-423.

[27] 孙可明, 辛利伟, 王婷婷, 等. 超临界CO2气爆煤体致裂规律模拟研究[J]. 中国矿业大学学报, 2017, 46(03): 501-506.

[28] 黄正红, 邓守春, 李海波. 拉伸荷载作用下含预制裂纹平板试样表面特征量演化规律研究[J]. 岩石力学与工程学报, 2019, 38(03): 527-541.

[29] 郭德勇, 吕鹏飞. 煤层深孔聚能爆破裂纹扩展数值模拟[J]. 煤炭学报, 2012, 37(2): 274-278.

[30] Jingcheng Liu, Hongtu Wang, Zhigang Yuan, Xiaogang Fan Experimental Study of Pre-splitting Blasting Enhancing Pre-drainage Rate of Low Permeability Heading Face [C]. First International Symposium on Mine Safety Science and Engineering Procedia Engineering, 26(2011): 818-823.

[31] Zhigang Liu, Yinghua Zhang, Zhian Huang, YukunGao, Yanfeng Zhang. Numerical simulating research on orifice pre-splitting blasting in coal seam [C]. 2012.

[32] Jie L, Xiaohong G, Shifei S, et al. Bibliometric Mapping of “International Symposium on Safety Science and Technology (1998-2012)”[J]. Procedia Engineering, 2014, 84: 70-79.

[33] 马小涛, 李智勇, 屠洪盛, 等. 高瓦斯低透气性煤层深孔爆破增透技术[J]. 煤矿开采, 2010, 15(1): 92-94.

[34] 弓美疆, 池摇鹏, 张明杰. 低透气性高瓦斯煤层深孔控制预裂爆破增透技术[J]. 煤炭科学技术, 2012, 40(10): 69-72.

[35] 许梦飞. 煤层中液态CO2相变致裂半径的研究[D]. 河南理工大学, 2016.

[36] Hongbing Xia, BaoYan. Application of Deep-hole Pre-cracking Blasting in the Preserved Roadway beside the Gob for Working Gaolin in Coal Seams [C]. 2012 International Conference on Future Energy, Environment, and Materials Energy Procedia 16 (2012): 828-835.

[37] Renshu Yang, Yanbing Wang, HuajunXue, Maoyuan Wang. Dynamic Behavior Analysis of Perforated Crack Propagation in Two-Hole Blasting [C]. 2012. International Conference on Structural Computation and Geotechnical Mechanics Procedia Earth and Planetary Science, 5(2012): 254-261.

[38] 吴小超. 爆生气体致裂作用试验研究[D]. 西安理工大学, 2017.

[39] 孙可明, 王金彧, 辛利伟. 不同应力差条件下超临界CO2气爆煤岩体气楔作用次生裂纹扩展规律研究[J]. 应用力学学报, 2019, 36(02): 466-472+516.

[40] 杨仁树, 丁晨曦, 王雁冰, 等. 爆炸应力波与爆生气体对被爆介质作用效应研究[J]. 岩石力学与工程学报, 2016, 35(S2): 3501-3506.

[41] 王雁冰. 爆炸的动静作用破岩与动态裂纹扩展机理研究[D]. 中国矿业大学(北京), 2016.

[42] 马小敏. 液态CO2相变致裂影响有效抽采半径试验研究[J]. 煤炭科学技术, 2019, 47(02): 88-93.

[43] 孙亮. 低透煤层CO2气相致裂卸压增透技术研究[J]. 煤炭技术, 2019, 38(10): 76-79.

[44] 周西华, 门金龙, 宋东平, 等. 液态CO2爆破煤层增透最优钻孔参数研究[J]. 岩石力学与工程学报, 2016, 35(03):5 24-529.

[45] 洪林, 马驰, 陈帅. CO2爆破布置参数数值模拟[J]. 辽宁工程技术大学学报(自然科学版), 2017, 36(10): 1026-1030.

[46] 彭高友, 高明忠, 吕有厂, 等. 深部近距离煤层群采动力学行为探索[J]. 煤炭学报, 2019, 44(07): 1971-1980.

[47] 廖文旺. 爆生气体作用下裂隙岩体裂纹扩展模式研究[D]. 吉林大学, 2019.

[48] 费鸿禄, 刘雨, 钱起飞, 等. 地应力作用下偏心装药的炮孔裂隙分布[J]. 黄金科学技术, 2020, 28(02): 228-237.

[49] 孙可明, 王金彧, 辛利伟. 超临界CO2气爆致裂爆生气体压力沿破裂面变化规律实验研究[J]. 实验力学, 2019, 34(04): 693-699.

[50] 周航. 超临界CO2气爆爆生气体管内流动及喷孔冲击应力变化规律实验研究[D]. 辽宁工程技术大学, 2019.

[51] 崔新男, 汪旭光, 张小军, 等. 基于数字图像处理技术的爆生气体膨胀规律研究[J]. 有色金属(矿山部分), 2019, 71(04): 119-123.

[52] DALLY J W. An introduction to dynamic photoelasticity[J]. Experimental Mechanics, 1980, 20(12): 409-416.

[53] CHO S H, NAKAMURA Y, MOHANTY B. Numerical study of fracture plane control in laboratory-scale blasting [J]. Engineering Fracture Mechanics, 2008, 75 (13): 3966-3984．

[54] ZHOU C, HU C, MA F, et al. Elastic wave scattering and dynamic stress concentrations in exponential graded materials with two elliptic holes[J]. Wave Motion, 2014, 51(3): 466-475.

[55] 岳中文, 郭洋, 许鹏, 等. 定向断裂控制爆破的空孔效应实验分析[J]. 爆炸与冲击, 2015, 35(03): 304-311.

[56] 陈秋宇, 李海波, 夏祥, 等. 爆炸荷载下空孔效应的研究与应用[J]. 煤炭学报, 2016, 41(11): 2749-2755.

[57] Z. W. Yue, L. Y. Yang, and Y. B. Wang. Experimental study of crack propagation in polymethyl methacrylate material with double holes under the directional controlled blasting[J]. Fatigue and Fracture of Engineering Materials and Structures, 2013, 42(5): 827–833.

[58] R. S. Yang, C. Chen, X. Wang et al. Experimental investigation on the influence of different diameter empty holes on the crack growth behavior of blasting[J]. Journal of China Coal Society, 2017, 42: 2498–2503.

[59] Meng Li, Zheming Zhu, Ruifeng Liu. Study of the effect of empty holes on propagating cracks under blasting loads[J]. International Journal of Rock Mechanics and Mining Sciences, 2018, 103: 225-237.

[60] 王泽军. 爆炸荷载作用下岩体裂纹扩展特性研究[D]. 北京交通大学, 2019.

[61] 朱必勇, 贺严, 焦文宇, 等. 直孔掏槽爆破中空孔效应的数值模拟研究[J]. 矿业研究与开发, 2020, 40(02): 58-61.

[62] Lu C P, Liu G J, Liu Y, et al. Microseismic multi-parameter characteristics of rockburst hazard induced by hard roof fall and high stress concentration[J]. International Journal of Rock Mechanics and Mining Sciences, 2015(76): 18-32.

[63] MBANDEZI M L, MABUZA R B. The effect of variations of crack geometry on the stress concentration factor in a thin plate using finite element method[C]. 18th World Conf. Nondestruct. Test. 2012: 16-20.

[64] Akano T T, Fakinlede O A, Olayiwola P S. On Analysis of Stress Concentration in Curvilinear Anisotropic Deformable Continuum Bodies[J]. Journal of Solid Mechanics, 2020, 12(2): 401-410.

[65] Weißgraeber P, Leguillon D, Becker W. A review of Finite Fracture Mechanics: crack initiation at singular and non-singular stress raisers[J]. Archive of Applied Mechanics, 2016, 86(1-2): 375-401.

[66] Li M, Xu J, Wang C, et al. Thermal and kinetics mechanism of explosion mitigation of methane-air mixture by N2/CO2 in a closed compartment[J]. Fuel, 2019, 255: 115-147.

[67] Ke B, Zhou K, Xu C, et al. Thermodynamic properties and explosion energy analysis of carbon dioxide blasting systems[J]. Mining Technology, 2019, 128(1): 39-50.

[68] Li X, Li C, Cao W, et al. Dynamic stress concentration and energy evolution of deep-buried tunnels under blasting loads[J]. International Journal of Rock Mechanics and Mining Sciences, 2018, 104: 131-146.

[69] Gao Q, Lu W, Yan P, et al. Effect of initiation location on distribution and utilization of explosion energy during rock blasting[J]. Bulletin of Engineering Geology and the Environment, 2019, 78(5): 3433-3447.

[70] Yuan W, Su X, Wang W, et al. Numerical study of the contributions of shock wave and detonation gas to crack generation in deep rock without free surfaces[J]. Journal of Petroleum Science and Engineering, 2019, 177: 699-710.

[71] Yang R, Ding C, Yang L, et al. Visualizing the blast-induced stress wave and blasting gas action effects using digital image correlation[J]. International Journal of Rock Mechanics and Mining Sciences, 2018, 112: 47-54.

[72] Ya Ma. Cn J. CHI I. A Iaser-speklestrain gage [J]. Journal of PhysisE: ScientificInstruments, 1981, 14: 1270-1273.

[73] Peters W H, Ranson W F. Digital Imaging Techniques In Experimental Stress Analysis[J]. Optical Engineering, 1982, 21(3):427-431.

[74] Bieniawski Z T. Proceedings of the 4th International Congress on Rock Mechanics [C], Montreaux, 1979.

[75] 李启月, 徐敏, 范作鹏, 等.直眼掏槽破岩过程模拟与空孔效应分析[J]. 爆破, 2011, 28(04): 23-26.

[76] 王学滨, 侯文腾, 潘一山, 等. 基于数字图像相关方法的单轴压缩煤样应变局部化过程试验[J]. 煤炭学报, 2018, 43(04): 984-992.

[77] 马少鹏, 潘一山, 王来贵, 等. 数字散斑相关方法用于岩石结构破坏过程观测[J]. 辽宁工程技术大学学报, 2005, 24(1): 763-763.

[78] 满轲, 刘晓丽. 周边空孔效应对爆破振速及围岩损伤的影响研究[J]. 工程力学, 2020, 37(11): 127-134+184.

[79] 雷战, 郭侃, 艾欣, 等. 爆炸荷载下炮孔与空孔间距对爆破作用的影响[J]. 火工品, 2020(05): 52-56.

[80] 周川云, 黄强, 张明明, 等. 超声波时差法检测技术在煤矿风速测量中的应用[J]. 矿业安全与环保, 2018, 45(03): 42-45+50.

[81] 纪翔. 孔周煤岩体渐进性破坏过程中超声波特性研究[D]. 西安科技大学, 2020.

[82] 周清, 张云海, 齐麟. LS-DYNA软件中4种不同爆炸荷载施加方法的比较[J]. 兵器装备工程学报, 2021, 42(02): 216-221.

[83] 周杰, 王凤英, 安文同, 等. 基于LS-DYNA的射孔弹侵彻煤层可行性探究[J]. 煤矿安全, 2020, 51(03): 164-167.

[84] 丁建新, 邱焕峰. 基于不连续有限元的拱坝应力应变仿真分析[J]. 武汉大学学报(工学版), 2018, 51(03): 198-204.

[85] 付佳佳, 陈必港, 尤涛, 等. “空孔效应”对光面爆破效果的影响分析[J]. 有色金属(矿山部分), 2017, 69(01): 44-49.

[86] 柴修伟, 李建国, 习本军, 等. 等体积空孔直眼掏槽槽腔形成过程及其分析[J]. 爆破, 2020, 37(04): 48-52.

[87] 李德波, 樊建人, 易富兴, 等. 面特征无反射边界条件处理关键问题的直接数值模拟[J]. 燃烧科学与技术, 2012, 18(05): 427-434.