Study on Influence of Soft Coal Interlayer on Mechanical Properties of Coal Under Uniaxial Compression

In order to explore the influence degree and law of soft structure coal interlayer on the uniaxial compression mechanical parameters and failure mode of primary coal samples, based on the macro-scopic mechanical parameters obtained from the indoor test, the standard coal samples with different thickness and dip structure soft coal interlayer are simulated by PFC2D software, and the micro mechanical response mechanism of the samples under load is analyzed. According to the test results, the uniaxial compression damage model of coal under the coupling action of soft structure coal interlayer and load is established, and the influence of structural coal occurrence parameters on the failure mode evolution of the sample is discussed. The results show that: the thickness of soft coal interlayer is an important parameter affecting the uniaxial compressive strength of composite coal seam samples. When the thickness of soft coal interlayer increases, the uniaxial compressive strength of samples in soft coal interlayer decreases. The dip angle of soft coal interlayer mainly affects the initiation and propagation mode of internal cracks. The larger the dip angle, the later the initiation time of shear cracks, and the smaller the proportion of shear cracks in the total number of cracks. There are three types of failure of soft coal intercalation: spallation failure along the interface, tensile failure and composite failure. The failure type is mainly related to the dip angle of soft coal intercalation.