Meikuang Anquan (Dec 2021)
Structural components and stress damage mechanism of coal and rock mass
Abstract
In order to study the distribution law and development mechanism of coal and rock mineral composition and fracture occurrence in its damage and failure process under static stress conditions, X-ray diffractometer(XRD) and electron microscope (SEM) are used to explore coal and rock mass. The mineral composition and surface fracture morphology of the solid skeleton are used to construct a visualized “block-composite” three-dimensional fracture structure using the discrete joint network model (DFN), and to compare the “load-displacement” curve of the coal block to complete the uniaxial compression of the composite simulation analysis. The results of the study show that the mineral components of the coal seam and surrounding rock samples are mainly kaolinite and quartz, and the content of the components of the diffraction angle changes are different. In addition, the surface body’s fissures are complex in arrangement and attached to natural defects(holes, cavities, cracks), indicating that the coal and rock mass formed by sedimentation has the characteristics of heterogeneity and multi-anisotropy; the macroscopic stress behavior of coal and rock entities under uniaxial compression goes through the four stages of “compaction-elasticity-plasticity-failure”; the randomly distributed disc-shaped fissures of various sizes in the composite body are divided into three types: single type, block type and penetration type according to the mutual intersection and interconnection scale. TypeⅠfractures reduce the pore volume at the initial stage of uniaxial compression. Over the compressed section of coal and rock mass, the block plastic zone presents a wide range of shear degradation; the type Ⅱ fracture contains triangular, quadrilateral and multilateral fractures which are squeezed by each other with the action of stress and cross friction, resulting in interblock shear slip to enter the elastic stage and maintain its structural stability; when the type III cracks are connected to each other and cause extensive tensile damage, they enter the unrecoverable plastic section, which will eventually lead to the failure of the block.
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