页岩结构面原位剪切特性及裂缝扩展试验研究

Experiment study on in-situ shearing characteristics and crack propagation of shale structural plane

针对次生断裂构造挤压形成倾角差异的外倾单斜页岩,通过原位直接剪切试验,研究页岩结构面抗剪强度特性与裂缝扩展模式。试验结果表明:页岩结构面剪切应力与剪切位移曲线具有明显的阶段性,当结构面倾角处于24°~30°时,岩体存在峰值强度与残余强度阶段,当结构面倾角处于30°~38°时,岩体处于无残余强度阶段;页岩压剪裂缝扩展形态主要有4种,即沿单一层面开启的单裂缝、沿多个层面开启的裂缝网、贯穿基质体的转向裂缝,以及沿天然裂缝尖端开启的裂缝;胶结较弱的结构面易形成裂缝,岩层薄弱处易发生裂缝方向转向并形成贯穿多个层面的"台阶状"裂缝网,在主裂缝周边会产生定向排列的"雁列式"裂缝,进一步扩展与结构面贯通,使得岩体形成多条贯通性裂缝;页岩结构面压剪试验裂缝贯通模式为结构面剪切贯通裂缝、基质体张拉贯通裂缝、天然裂缝处张拉贯通裂缝、拉剪复合型贯通裂缝。研究成果有利于进一步认识倾斜岩层层面剪切力学特性,为顺层岩质边坡稳定性评价提供参数。

Aiming at the outward dipping monoclinic shale with different dip angles formed by the compression of the secondary fault structure, the shearing strength characteristics and crack propagation mode of the shale structural plane are studied through the relevant in-situ direct shear experiment. The experiment result shows that both the shear stress and the shear displacement curves of the shale structural plane are obviously phased. When the dip angle of the structural plane is 24°~30°, the rock mass has both peak strength and residual strength phases, while the rock mass has no residual strength phase when the dip angle of the structural plane is 30°~38°. Four kinds of the propagation modes of the compressive-shear crack of the shale are mainly there for the shale, i.e. the single crack opened along a single layer, the crack-network opened along several layers, the direction-turning crack through the rock matrix body and the crack opened along the tip of the natural crack. Crack is prone to be formed on the weakly cemented structural plane, while the turning of the crack direction is prone to occur at the weak location of the rock and forms the stepped crack-network through several layers, from which the orientatedly distributed en echelon cracks are to be caused around the main crack and then further propagate and break through the structural plane to make the rock mass form several penetrated cracks. The crack breakthrough modes in the compressive shear experiment of the shale structural plane are shearing and penetrating crack of the structural plane, the tensile-penetrating crack of rock matrix body, the tensile-penetrating crack of natural crack and the tensile-shear composite penetrating crack. The study results are helpful to further understand the shearing mechanical characteristics of the inclined rock layers for providing the relevant parameters to the evaluation of the stability of the bedding rock slope.