关键词: 梯级递增式加载, 单向约束, 开孔扰动, 局部变形

Abstract: To explore the stress-strain evolution law and failure mechanism of coal and rock samples with central holes under the real mining effect，taking the coal and rock samples with central holes as the re⁃ search object，the macroscopic failure forms were experimentally studied by using the self-developed unidi⁃ rectional constraint incremental loading device for standard square coal and rock samples，the stress-strain monitoring system and the image capture system. The results show that during the elastic deformation stage， under the action of cascade increasing loads，the stress-strain during the elastic deformation stage of the open-hole disturbed coal and rock mass and the local crack evolution during the failure stage present a stress concentration phenomenon. The larger the diameter of the borehole，the more significant the stress concentration phenomenon. The strain at each monitoring point around the borehole shows a certain anisotro⁃ py，that is，the compressive strain at the vertical and horizontal edges of the borehole is relatively large. Strain in the same direction as the loading has an obvious edge effect at the loading surface，but the exis⁃ tence of horizontal binding force will weaken this effect. The horizontal binding force will enhance the overall and local failure strength of the specimen to a certain extent，but it will not affect the strain value when local failure occurs in the specimen. The increase in the diameter of the borehole intensifies the stress concentra⁃ tion effect，while the horizontal binding force can optimize the bearing capacity of the coal and rock mass and suppress the uneven distribution of tensile strain.

Key words: cascade increasing loading, one-way constraint, disturbance of opening hole, local defor? mation