层状砂岩各向异性力学特性试验研究

Experimental study on anisotropic characteristics of bedded sandstone

岩体的各向异性力学特性对工程安全稳定具有至关重要的影响。针对工程中常见的层状砂岩,设计进行0°,15°,30°,45°,60°,75°和90°等7种层理角度的单轴和三轴压缩试验,详细分析层理角度对岩体力学特性和破坏模式的影响。研究结果表明:(1)不同层理角度岩样的应力–应变曲线形态基本一致,均包括压密阶段、弹性阶段、屈服阶段和破坏阶段,随着层理角度的增加,应力–应变曲线的压密阶段逐渐变短;(2)在单轴和三轴压缩状态下,层状砂岩各向异性特性明显,层理角度从0°增大到90°,弹性模量逐渐增大,而变形模量、抗压强度、黏聚力和摩擦角先减小后增大,呈U型分布,在0°或90°时达到最大值,60°左右时达到最小值;(3)随着围压的增大,其对层理弱面开裂滑动的限制作用逐渐增强,层理弱面对岩样的破坏模式影响效应逐渐减弱,不同层理角度岩样的力学参数差别逐渐减小,岩样的各向异性特性逐渐减弱;(4)层状砂岩的破坏模式与层理角度和围压的关系密切,可以归纳为3种类型:劈裂张拉破坏、顺层理弱面的剪切滑移破坏、局部顺层理弱面和局部穿越基质、层理弱面的复合剪切破坏。研究结论可为层状砂岩相关的工程变形稳定分析提供参考。

The anisotropic characteristics of rock mass affect crucially the engineering stability and safety. The uniaxial and triaxial compression tests on 7 kinds of bedding angles（0° , 15° , 30° , 45 ° , 60° , 75° , 90° ） were designed according to the common bedding sandstone in engineering. The results show that the stress-strain curves under different kinds of bedding angles have basically the same shape with a compaction stage, an elastic stage, a yielding stage and a failure stage. The compression stage of the stress-strain curve becomes shorter with the increasing of the bedding angle. Significant anisotropy of the bedding sandstone is observed under the uniaxial and triaxial compression tests. The elastic modulus increases gradually but some mechanical parameters, such as the deformation modulus, compressive strength, cohesion and friction angle, decrease firstly and then increase to exhibit a U-shaped curve as the bedding angle varies from 0° to 90° , and reach the maximum value at 0 o or 90 °, the minimum value at about 60°. With the increasing of confining pressure, both the difference of mechanical parameters between different bedding angles and the anisotropic characteristics of bedding rock sample decrease gradually. The limitation of confining pressure to the crack and slip of weak bedding face gradually increased, but the effect of weak bedding face to the failure modes of rock sample weakened gradually. The failure modes of bedding sandstone are closely related to the bedding angles and confining pressures, which can be summed up in three types： tensile splitting, shearing slip damage along the weak bedding face, compound shear failure across and along the weak bedding face.