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与沉积岩的局部缺陷不同,煤层具有分布的裂隙和弱面,不仅影响强度,也会影响变形。煤样单轴压缩的强度和杨氏模量离散性很大,但两者具有明显的相关性。在围压下压缩时,闭合裂隙可以通过摩擦承载,使煤样强度和杨氏模量的离散性减小。不同煤块加工的试样强度不同,但围压对三轴强度的影响系数K相同,即内摩擦系数是一个材料参数,因而可以对不同煤块的试验结果进行联合回归。这不仅可以消除煤块的差异对内摩擦系数的影响,而且可以评价煤块强度的离散程度。
Different from the local defects of sedimentary rocks, the coal seam has distributed fractures and weak planes, which not only affect the strength but also affect the deformation. The uniaxial compressive strength and Young’s modulus of the coal samples are very discrete, but the two have obvious correlations. When compressing under confining pressure, the closed fractures can be carried by friction, so that the strength of coal sample and the Young’s modulus dispersion decrease. The strength of specimens with different coal briquets is different, but the influence coefficient K of the confining pressure on triaxial strength is the same, that is, the internal friction coefficient is a material parameter so that the test results of different briquettes can be combined and regressed. This can not only eliminate the influence of the difference of coal blocks on the internal friction coefficient, but also evaluate the degree of dispersion of the coal block strength.