汪家寨煤岩各向异性的力学特性研究

Study on the Mechanical Properties of Anisotropy of Wangjiazhai Coal-Rock

煤岩具有典型的层理构造,导致煤岩具有显著的各向异性特征。采集贵州大河边向斜区内汪家寨煤矿井下工作面11号原煤,制备了与层理面呈不同夹角(0°/30°/45°/60°/90°)的煤岩试样,系统开展了超声波速测试、单轴和三轴压缩试验研究,从各个角度研究煤岩各向异性特征。结果表明:超声波速显示煤岩的各向异性明显,说明与层理不同夹角方向煤岩内部密实程度不同;单轴压缩试验下,抗压强度和弹性模量均表现出高度的角度效应,0°和90°试样最高、45°最低,整体呈近似“U”形分布;三轴压缩试验下,强度和变形也具有显著的角度效应,0°和90°试样的峰值强度和峰值应变均较大,且均为穿层理剪切破坏,中间角度的强度和变形能力相对较弱,以顺层理或与层理呈小夹角剪切破坏为主;黏聚力和内摩擦角随层理交角大体呈两边高、中间低的变化趋势,其本质上反应的是基质与层理的抗剪性能差异;可以用横观各向同性模型表征煤岩的各向异性特征,并获得了5个独立参数。该研究揭示了汪家寨煤岩的各向异性的变形与强度特征,可为同类煤储层井壁稳定性评价、压裂设计及缝网扩展分析等提供重要理论依据及技术指导。

Coal-rock has a typical bedding structure,which results in obvious anisotropy of coal-rock.No.11 raw coal was collected from Wangjiazhai Coal Mine in the syncline area of Dahebian,Guizhou,and coal samples with different angles(0°/30°/45°/60°/90°)to bedding were prepared.To study the anisotropic characteristics of coal-rock from different angles,ultrasonic velocity tests,uniaxial and triaxial compression tests were systematically carried out.The results show that:Ultrasonic velocity has an obvious influence on the anisotropy of coal and rock,which indicates that the internal compactness degree of coal-rock at different angles is different.Under the condition of the uniaxial compression test,the compressive strength and elastic modulus show a great angular effect.The compressive strength of 0°and 90°samples is the highest,and the compressive strength of 45°samples is the lowest,showing a"U"shape distribution.Under the condition of the triaxial compression test,the strength and deformation also have an obvious angular effect.The peak strength and peak strain of 0°and 90°specimens are larger,which are all destroyed by bedding shear.The strength and deformability of the middle corner are much weaker,mainly due to shear failure along with bedding or at a small angle to bedding.The cohesion and internal friction angle tend to be higher at both ends and lower at the middle with the increase of bedding intersection angle.In essence,it reflects the difference of shear properties between matrix and bedding.The transversely isotropic model can be used to characterize the anisotropy of coal and rock,and five independent parameters are obtained.The study reveals the anisotropic deformation and strength characteristics of Wangjiazhai coal-rock mass,which provides an important basis for coalbed methane fracturing design and reservoir reconstruction in this block and similar structural areas.