层状组合砂岩强度及变形特性试验研究

Experimental Study on Strength and Deformation Characteristics of Layered Composite Sandstone

为研究煤矿层状砂岩顶板失稳破坏机理,明确岩石的厚度比对岩石力学性质的影响,选取两种强度比为1∶1.12的砂岩进行了不同组合的单轴压缩试验。结果表明:不同组合的砂岩,随着红砂岩厚度的增加,抗压强度、弹性模量变化范围较小,但红砂岩占比0.8的组合砂岩,上下端部存在10mm的较软岩石,消除了端面效应,吸收部分能量,改变了试样的破坏模式,导致其强度高;最先产生裂纹的位置受交界面的影响,无粘结试样的裂纹最初产生在交界面,有粘结试样的裂纹最初产生于端部,峰后破坏呈现明显的阶段性特征;组合砂岩的破坏模式主要有剪切滑移型、折线剪切劈裂型、贯通劈裂剪切型破坏3种;白砂岩厚度大的试样,破碎分维与抗压强度成正比,红砂岩厚度大的试样,破碎分维与抗压强度成反比。

In order to study roof failure mechanism of the layered sandstone in coal mine and to determine the influence of rock thickness ratio on the mechanical properties of rock,uniaxial compression experiments on two kinds of composite sandstones samples with strength ratio of 1∶1.12 were carried out.The results show that:compressive strength and elastic modulus of the composite sandstones have small change range with the increase of red sandstone thickness.However,when the red sandstone thickness accounts for 0.8 of the thickness of total composite sandstone,the composite sandstone exists 10 mm of soft rock at the upper and lower ends,which eliminates the end effect,absorbs part of the energy and changes the failure mode of the sample,resulting in high strength.The crack generation position is affected by the interface,the crack of not-bonded sample is generated at the interface,and the crack of the bonded sample is generated at the end.Post-peak destruction presents stage characteristics.The failure modes of composite sandstone mainly include shear slip type,fold-line shear splitting type,and connecting splitting shear type.For the samples with large thickness of white sandstone,the fracture fractal dimension is proportional to the compressive strength;for samples with large thickness of red sandstone,the fracture fractal dimension is inversely proportional to the compressive strength.