稳压约束下钻孔倾角对煤体抗压强度影响实验研究
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摘要
顺层钻孔预抽煤层瓦斯是降低其含量的主要方法之一,为研究采动应力对本煤层不同倾角抽采钻孔稳定性的影响,开展了稳压条件下,无钻孔和钻孔倾角为0°,15°,30°的型煤单轴压缩试验,对比分析了钻孔倾角对稳压约束下型煤的应力-应变曲线、强度特征、破坏形态以及损伤程度的影响。结果表明:稳压压力为500N,增大钻孔倾角对煤样抗压强度、弹性模量有明显的劣化作用,劣化率最大达到32%;含钻孔型煤的破坏形态表现为由孔周出现2组较为明显的对称裂隙,其中1条主裂隙持续演化最终导致试件完全破坏;随着钻孔倾角的增大,裂纹闭合应力增大,而起裂应力和致损应力减小,同时,试件总裂纹面积分数也减小,钻孔周围煤体更容易失稳。
In-seam borehole gas pre-drainage is one of the most effective methods to reduce gas content. To investigate the effects of mining stress on stability of boreholes with different dip angles, uniaxial compression experiments under constant pressure constraint were conducted. The testing series include no borehole and different borehole dip angles of 0°, 15° and 30°. The effects of borehole dip angle on coal stress-strain curves, strength characteristics, failure modes, and damage degree were analyzed.Results show that, when constant pressure is 500 N, the coal compressive strength and elasticity modulus have a significant deteriorative performance with the increase in borehole dip angle, and the maximum value of degradation rate could reach up to 32%. The damage form of briquette show as two distinct symmetry fractures around borehole. Meanwhile, one of above two fractures continuously develops and results in complete specimen destruction. With the increase in borehole dip angle, the fracture closure stress rises, while the crack stress and damage stress gradually decrease. At the same time, the total crack area fraction decreases, and the coal around borehole is more likely to experience instability.
In-seam borehole gas pre-drainage is one of the most effective methods to reduce gas content. To investigate the effects of mining stress on stability of boreholes with different dip angles, uniaxial compression experiments under constant pressure constraint were conducted. The testing series include no borehole and different borehole dip angles of 0°, 15° and 30°. The effects of borehole dip angle on coal stress-strain curves, strength characteristics, failure modes, and damage degree were analyzed.Results show that, when constant pressure is 500 N, the coal compressive strength and elasticity modulus have a significant deteriorative performance with the increase in borehole dip angle, and the maximum value of degradation rate could reach up to 32%. The damage form of briquette show as two distinct symmetry fractures around borehole. Meanwhile, one of above two fractures continuously develops and results in complete specimen destruction. With the increase in borehole dip angle, the fracture closure stress rises, while the crack stress and damage stress gradually decrease. At the same time, the total crack area fraction decreases, and the coal around borehole is more likely to experience instability.
引文
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[16]陈新,吕文涛,孙靖亚.基于图像分析的节理岩体单轴压缩损伤演化研究[J].岩石力学与工程学报,2014,33(6):1149-1157.CHEN Xin,LYU Wentao,SUN Jingya.Study on uniaxial compression damage evolution of jointed rock mass based on image analysis[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(6):1149-1157.
[2]郤保平,赵阳升.高温高压下花岗岩中钻孔围岩的热物理及力学特性试验研究[J].岩石力学与工程学报,2010,29(6):1245-1253.XI Baoping,ZHAO Yangsheng.Experimental research on thermal physics and mechanical properties of surrounding rocks in granite under high temperature and pressure[J].Chinese Journal of Rock Mechanics and Engineering,2010,29(6):1245-1253.
[3]赵阳升,郤保平,万志军,等.高温高压下花岗岩中钻孔变形失稳临界条件研究[J].岩石力学与工程学报,2009,28(5):865-874.ZHAO Yangsheng,XI Baoping,WAN Zhijun,et al.Study of critical conditions for deformation instability of bored holes in granite under high temperature and pressure[J].Chinese Journal of Rock Mechanics and Engineering,2009,28(5):865-874.
[4]郤保平,赵阳升,万志军,等.高温静水应力状态花岗岩中钻孔围岩的流变实验研究[J].岩石力学与工程学报,2008,27(8):1659-1666.XI Baoping,ZHAO Yangsheng,WAN Zhijun,et al.Study on rheological behavior of surrounding rock in drilling granite under hydrothermal condition[J].Chinese Journal of Rock Mechanics and Engineering,2008,27(8):1659-1666.
[5]冯子军,赵阳升,赵金昌,等.高温静水压力下钻进过程中花岗岩体变形特征[J].岩石力学与工程学报,2010,29(增刊2):4108-4112.FENG Zijun,ZHAO Yangsheng,ZHAO Jinchang,et al.Deformation characteristics of granite bodies during drilling at high hydrostatic pressure[J].Chinese Journal of Rock Mechanics and Engineering,2010,29(Sup 2):4108-4112.
[6]HAIMSON B.Micromechanisms of borehole instability leading to breakouts in rocks[J].International Journal of Rock Mechanics&Mining Sciences,2007,44(2):157-173.
[7]马少鹏,王来贵,赵永红.岩石圆孔结构破坏过程变形场演化的实验研究[J].岩土力学,2006,27(7):1082-1086.MA Shaopeng,WANG Laigui,ZHAO Yonghong.Experimental study on evolution of deformation field in failure process of rock round hole structure[J].Rock and Soil Mechanics,2006,27(7):1082-1086.
[8]周喻,刘冰,王莉,等.单轴压缩条件下含双圆孔类岩石试样力学特性的细观研究[J].岩石力学与工程学报,2017,36(11):2662-2671.ZHOU Yu,LIU Bing,WANG Li,et al.Meso-mechanical study on mechanical properties of double-round rock specimens under uniaxial compression[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(11):2662-2671.
[9]石占山,梁冰,王岩,等.加载与卸载过程瓦斯抽采钻孔变形特征[J].煤炭学报,2017,42(6):1458-1465.SHI Zhanshan,LIANG Bing,WANG Yan,et al.Deformation characteristics of gas drainage borehole during loading and unloading[J].Journal of Coal Research,2017,42(6):1458-1465.
[10]姚向荣,程功林,石必明.深部围岩遇弱结构瓦斯抽采钻孔失稳分析与成孔方法[J].煤炭学报,2010,35(12):2073-2081.YAO Xiangrong,CHENG Gonglin,SHI Biming.Analysis of borehole instability and formation of borehole in gas drainage with weak structure in deep surrounding rock[J].Chinese Journal of Coal Studies,2010,35(12):2073-2081.
[11]刘春,周福宝.松软煤层瓦斯抽采钻孔塌孔失效特性及控制技术基础[D].中国矿业大学,2014.
[12]薛飞,张农.无煤柱煤与瓦斯共采中抽采钻孔采动破坏机理研究[D].中国矿业大学,2015.
[13]钱鸣高,石平五,许家林.矿山压力与岩层控制.第2版[M].徐州:中国矿业大学出版社,2010:15-17.
[14]王洪亮,范鹏贤,王明洋,等.应变率对红砂岩渐进破坏过程和特征应力的影响[J].岩土力学,2011,32(5):1340-1346.WANG Hongliang,FAN Pengxian,WANG Mingyang,et al.Effect of strain rate on gradual failure process and characteristic stress of red sandstone[J].Rock and Soil Mechanics,2011,32(5):1340-1346.
[15]姚国圣,李镜培,谷拴成.考虑岩体扩容和塑性软化的软岩巷道变形解析[J].岩土力学,2009,30(2):463-467.YAO Guosheng,LI Jingpei,GU Shuancheng.Analysis of deformation of soft rock tunnel considering capacity expansion and plastic softening of rock mass[J].Rock and Soil Mechanics,2009,30(2):463-467.
[16]陈新,吕文涛,孙靖亚.基于图像分析的节理岩体单轴压缩损伤演化研究[J].岩石力学与工程学报,2014,33(6):1149-1157.CHEN Xin,LYU Wentao,SUN Jingya.Study on uniaxial compression damage evolution of jointed rock mass based on image analysis[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(6):1149-1157.