层理板岩巴西劈裂破坏模式的方向效应研究

Directivity Effect of Failure Mode of Layered Slate Under Brazilian Split Test

以贵州铜仁市某矿山层理板岩为研究对象,对其微观结构进行观测分析,然后选取7组不同θ角(加载方向与层理法向夹角)试样进行巴西劈裂试验。结果表明:在微观结构上,赤铁矿等刚性颗粒呈基底式胶结于黏土矿物中,层理面为软弱面;板岩的破坏模式存在显著方向效应,抗拉强度随夹角增大而减小;破坏模式总体上可分为4类,θ为0°时是基质拉伸型破坏,基质被逐层劈裂致使试样破坏,抗拉强度最大;θ为15°和30°时为基质拉剪型破坏,主要由于破坏面处的剪应力大于板岩基质的剪切强度致使试样破坏;θ为45°、60°、75°时为层理拉剪型破坏,层理面处的剪应力大于剪切强度时发生破坏;θ为90°时为层理拉伸型破坏,此时完全由于层面受张拉而破坏。

In order to reveal the contributions of bedding direction to layered slate's failure mode,firstly,microstructure observations were made out with high-power microscope.Secondly,Brazilian split tests were carried out with seven different anglesθ,which is between the loading direction and the normal direction of bedding.All the experiment samples were taken from a slate mine in Tongren city of Guizhou,China.The experimental results show that Hematite and other rigid particles were basal type cementation in clay minerals.Cohesion of bedding planes are weak.Slate failure modes have significant directional effect,and tensile strength decreases with the increase ofθ.Four kinds of failure modes can be obtained as follows,the first failure mode is tension destruction of matrix when θ=0°,matrix is destroyed by splitting layer by layer,tensile strength is the largest.The second failure mode is shear failure of matrix when θ= 15°,30°,while the shear stress in crack is greater than the shear strength of matrix,the sample will break.The third failure mode is shear failure of bedding when θ = 45°,60°,75°,while the shear stress in bedding planes is greater than the shear strength of bedding,the sample will break.The fourth failure mode is tension destruction of bedding when θ=90°,the bedding will stretch under tension.