Abstract: The research of the coal-rock system composed of deep coal seams and surrounding rock masses has become one of the popular research directions in deep mining. In this study, the L-shaped mold is used to carry out the unilateral confinement compression test on the rock-coal-rock combination, and the digital image correlation technology (DIC) and the particle flow PFC2D are used to analyze the test strength, failure characteristics and crack distribution of the coal-rock combination. (1) The main strain areas of coal-rock combination are all concentrated on the free side of the sample coal seam. (2) Under unilateral confinement, the joint restriction of the two rock layers on the coal seam decreases as the height-to-width ratio of the coal seam increases. The damage of the sample is gradually transferred from the middle of the coal seam to the end of the coal seam. (3) When the ratio of coal-rock combination is 1:1:1 and 1:2:1, the failure mode of the calculation model shows a <-shaped fracture, which appears on the free side in the middle of the coal seam. When the rock-to-rock ratio is 1:4:1, the macroscopic damage gradually shifts to the middle and upper part of the coal seam, and evolves into shear failure. (4) The microscopic cracks of the calculation model are mainly located on the free side, which appear as tensile cracks. The number of the tensile cracks inside the model are about 4.5 times that of the shear cracks.

Key words: coal-rock combination, unilateral confinement compression, digital image correlation technology, particle flow code, fracture mechanism