煤层钻孔降倾-控变-耗能防冲机制试验研究

Experimental study of rock burst prevention mechanism of bursting liability reduction-deformation control-energy dissipation based on drillhole in coal seam

对预制钻孔试样开展单轴压缩试验,采用声发射(acousticemission,简称AE)及数字图像相关(digitalimage correlation,简称DIC)监测技术探究多列多排布置钻孔试样的力学响应特征,分析钻孔对试样冲击倾向性、变形破坏及能量积聚与释放的影响规律。试验结果表明:煤层钻孔具有降低煤体冲击倾向、引导和控制煤体变形、增加变形能耗散的作用。(1)钻孔试样的强度较完整试样显著衰减,且随钻孔数增多,应力峰前弹性模量、应力峰值、冲击能量指数逐渐降低,冲击倾向性减弱。钻孔提升了AE事件的活动强度,但降低了高能量事件的占比。(2)钻孔布置方式改变了试样的破裂模式。完整试样由其表面中部形成应变局部化区域,并以该区域为弱面发生最终破裂;单列多排钻孔试样在钻孔上下侧起裂,产生局部化带,并向上下延伸形成宏观裂隙;双列多排钻孔试样在同排钻孔间的岩桥内起裂,然后垂直钻孔间岩桥内的裂隙进一步发育,最终形成纵横及斜交的宏观裂隙。钻孔展现出诱导试样提升垂直钻孔方向变形、约束平行钻孔方向变形、增强垂直方向变形、减小体积变形的空间效应。(3)钻孔能够降低变形能密度增长速率UV及变形能密度峰值Umax,同时延缓破坏时刻变形能的释放速率URV,且钻孔数越多,变形能密度峰值Umax及释放速率URV降低幅值越大。

Uniaxial compression experiments were carried out on prefabricated borehole samples.Acoustic emission(AE)and digital image correlation(DIC)monitoring technology were applied to explore the mechanical response characteristics of samples arranged in multiple rows and lines,and analyze the influence of the drillhole on the bursting liability,deformation and failure,accumulation and release of energy of coal samples.The results show that,destressing drillhole in coal seam could reduce the bursting liability,control the deformation and increase the deformation energy dissipation of samples.Compared with an intact sample,the strength of the samples with drillhole was significantly attenuated,and as the number of drilling rows increased,the pre-peak elastic modulus,peak stress,and the bursting energy index KE gradually decreased,and the bursting liability was reduced.Destressing drillhole could increase the activity intensity of AE events and reduce the proportion of high-energy events.The layout of the destressing drillhole caused change of the fracture mode of the samples.A strain localization area generates from the middle on the sample surface of the intact samples,and the final fracture occurs in this area as the weak surface.For the samples with single row and multiple lines of drillhole arrangement,cracks occur on the upper and lower sides of drillholes,forming a localization zone,which extend up and down to form macroscopic cracks.For the samples with double rows and multiple lines drillhole arrangement,cracks easily occur in the rock bridge between the same row of drillholes,and then the cracks in the rock bridge between the vertical drillholes further develope,and finally form the vertical and horizontal and oblique macroscopic cracks.Morevoer,the drillhole in sample could increase the vertical drilling direction(x-direction)deformation,reduce the parallel drilling direction(y-direction)deformation,enlarge the vertical direction(z-direction)deformation,and reduce the volume deformation.The drillholes could reduce the growth UV and peak value Umax of deformation energy density,and delayed the release rate URV of deformation energy at the moment of failure.When drillhole number is greater,the reduction amplitude of the peak deformation energy density Umax and the release rate URV are greater.