粉砂质板岩力学特性及各向异性特性

Mechanical and anisotropic properties of silty slates

为研究鄂西北地区板岩的力学特性及各向异性特征,开展了志留系粉砂质板岩的单轴压缩和巴西劈裂试验,分析了试样的力学特性和各向异性特征以及在不同荷载作用下的变形破坏模式,揭示了不同破坏模式的力学机制,并通过数值分析研究了不同板理面角度板岩边坡破坏模式及力学机制。研究结果表明,粉砂质板岩中的板理面是影响岩体力学行为的弱面,使得粉砂质板岩表现出明显的各向异性的特征。在单轴压缩条件下,粉砂质板岩在垂直板理面方向比平行板理面方向更易变形,变形量更大;平行板理面方向加载时试样破坏类型为竖向劈裂型张拉破坏,其实质是压杆失稳;垂直板理面加载时试样的破坏类型为穿切板理面的劈裂型剪切破坏;所测得的力学参数各向异性也较明显。在劈裂荷载作用下,粉砂质板岩的破坏模式主要有张拉劈裂破坏和沿板理面剪切破坏两种,所得抗拉强度在平行板理面方向上最大,在垂直板理面方向上最小,两个方向上的抗拉强度均小于抗压强度。由于板理面间的抗拉强度极低,在受到与板理面呈小角度相交的劈裂荷载作用时,容易产生沿板理面的张拉劈裂或拉剪破坏,在实际工程中应尽量避免板理面间的受拉破坏和沿板理面的拉剪破坏。在边坡工程中,板理面倾向、倾角对边坡破坏模式及力学机制有较大影响,边坡防护治理需充分考虑这一影响。上述研究为粉砂质板岩区岩质边坡防护治理以及其他岩石工程设计与施工提供理论依据与技术基础。

In this study, the uniaxial compression test and Brazilian splitting test were carried out on Silurian silty slates in northwest Hubei province to investigate their mechanical and anisotropic properties. The anisotropic mechanical properties and deformation failure modes of specimens were analysed under different loading conditions, and the corresponding mechanisms of different failure modes were revealed. Meanwhile, the numerical analysis was used to study failure modes and mechanical mechanisms of slate slopes with different angles of bedding planes. The results showed that bedding planes in silty slates were weak surfaces that affected mechanical properties of rock mass, resulting in obvious anisotropic characteristics of the silty slates. Under the uniaxial compression condition, the deformation of silty slates were easier in the direction of the vertical bedding plane than that of the parallel plane, and their deformation was more significant. The failure mode of the specimen was the vertical splitting tensile failure when the direction of the parallel plane was loaded, while the failure mode was the splitting shear failure cutting the bedding planes when the direction of the vertical plane was loaded. The anisotropy of measured mechanical parameters was relatively apparent. Under the action of splitting load, the failure modes of silty slates mainly included the tensile splitting failure and shear failure along the bedding plane. The obtained tensile strength was the largest in parallel bedding plane direction and was the smallest in the vertical bedding plane direction. The tensile strengths in both directions were lower than the compressive strengths. As the tensile strength between bedding planes was extremely low, tension-split failure or tension-shear failure was easily caused by the splitting load that intersected with the bedding plane at a small angle. Hence, the tension failure or tension-shear failure along bedding planes should be avoided as far as possible in practical engineering. The dip directions and angles of slates have great influences on failure modes and mechanics of slates slopes, which should be considered in the protection and treatment of rock slopes. Therefore, the results provide significant references for the protection and treatment of rock slopes, design and construction of other rock engineering projects in the distribution area of silty slates.