黑色页岩力学特性及各向异性特性试验研究

EXPERIMENTAL STUDY ON MECHANICAL AND ANISOTROPIC PROPERTIES OF BLACK SHALE

为了研究黑色页岩的力学特性和各向异性特征,对下寒武统牛蹄塘组黑色页岩行地化参数分析,牛蹄塘组黑色页岩的脆性矿物成分高达79.01%;利用扫描电镜获得页岩的微观结构,牛蹄塘组黑色页岩具有明显的层状沉积特征和层状薄片矿物结构。利用东北大学和长春朝阳试验仪器有限公司联合研制的ROCKMAN207系统对不同层理角度的黑色页岩试样进行三轴压缩试验,获得黑色页岩试样的全应力–应变曲线和破坏模式,并对比分析围压和层理角度对黑色页岩力学行为和破坏模式的影响。结果表明:(1)黑色页岩应力–应变曲线无明显的孔隙、裂隙压密阶段,峰前应力–应变曲线近似为直线段。(2)黑色页岩的破坏模式与围压条件和层理面角度有关,低围压条件下,黑色页岩破裂后易形成较为复杂的裂隙网络;轴向加载方向与黑色页岩层理平行时,易形成复杂的裂隙网络。(3)黑色页岩具有波速和强度各向异性的特征,随着层理角度的增加,黑色页岩的波速呈现降低的趋势,黑色页岩各向异性强度特征曲线形状近似为U型;黑色页岩的强度各向异性系数随着围压的增加逐渐降低。

Geochemical parameters of lower Cambrian black shale at Niutitang were measured in order to study the mechanical and anisotropic properties of black shale. The brittle mineral content of the lower Cambrian black shale at Niutitang was found to be as high as 79.01%. The scanning electron microscopy was used to obtain the microscopic structure of the black shale. The layered sedimentary characteristics and the lamellar structure of alternating plates were observed to exist in the black shale. Series of triaxial compression experiments on the black shale samples with different angles of bedding were carried out with the testing system ROCKMAN207,which was developed by Northeastern University and Chaoyang testing instrument company at Changchun. The whole stress-strain curves and failure modes were obtained. The effects of confining pressure and the angle of bedding on the mechanical behavior and failure modes of shale were analyzed. The stress-strain curves of the black shale exhibited no obvious stage of compaction of fissures and pores,and were largely straight lines ahead of the peak point. The failure modes of the black shale were related to the confining pressure and the angle of bedding. Under the condition of low confining pressure,complex networks of fractures were formed easily after the failure of the rock sample. When the axial loading direction was parallel to the shale′s bedding,the complex fracture networks were formed more easily. The wave velocity of the black shale samples decreases with the increase of the bedding angle. The anisotropic strength curve of the shale is U-shaped. The anisotropic coefficient of the black shale decreases with the increase of confining pressure.