稳压条件下煤体稳定特性钻孔倾角效应的试验研究

Experimental study for the effects of drilling angle on coal mass stability under stable pressure conditions

为研究不同钻孔倾角对煤体稳定特性的影响,应用三维全场应变测量分析系统(XTDIC)和声发射监测系统,开展稳压条件下无钻孔及钻孔倾角为0°,10°,20°,30°的型煤单轴压缩试验,分析了不同钻孔倾角试件强度特征、变形破裂特征及其对煤体稳定性的影响机理。结果表明:增大钻孔倾角对试件抗压强度、弹性模量有不同程度劣化作用,与无钻孔试件相比,劣化率最大达33.92%;根据试件加载过程中的声发射特征参数与加载时间的关系,将其划分为初始加载、稳压、峰前弹塑性和峰后应变软化4个阶段,随着钻孔倾角的增大,声发射计数与能量的增长速率逐渐减小;试件钻孔周围破坏形态呈偏"Y"状,30°倾角钻孔试件的损伤变量曲线出现明显台阶式递增现象;试件变形破坏过程是能量积聚与耗散的过程,随钻孔倾角增大,弹性应变能、耗散能、总能量、能量耗散率均减小;该研究指导了贵州某矿本煤层预抽钻孔布置,利用定向钻机尽可能保证钻孔轨迹为水平,钻孔稳定性较高,瓦斯抽采效果良好。

To study the effect of different drilling angles on the stability of coal mass, 3D measurement and analysis system for strain(XTDIC) and acoustic emission monitoring system are used to conduct uniaxial compression tests for briquettes without boreholes and with drilling angles of 0°, 10°, 20°, 30° under stable pressure conditions. The strength characteristics and deformation and fracture features of specimens with different drilling angles and their influence mechanism on coal mass stability are analyzed. The results show that increasing the drilling angle can weaken the compressive strength and elastic modulus of the specimens. Compared with the specimens without borehole, the strength weakening degree can up to 33.92%. Based on the relationship between the acoustic emission characteristic parameters and the loading time during the loading process of the specimens, it can be divided into four stages: initial loading, stable pressure, elastoplasticity before peak, and strain softening after peak. With the increase of drilling angle, the increasing rates of acoustic emission count and energy decreases gradually. The failure patterns around the boreholes shows a "Y" shape, and the damage variable curve of the specimen with a drilling angle of 30° shows a "stepped up" phenomenon. The deformation and failure of the specimen is the process of energy accumulation and dissipation. With the increase of drilling angles, the elastic strain energy, dissipated energy, total energy, and energy dissipation rate decrease. The research provides a guidance on arranging the pre-drainage borehole in this coal seam of a mine in Guizhou. The directional borehole rigs are used to control that the borehole trajectory is as horizontal as possible, and the gas drainage effect is good.