In this study, considering the scale effect of rock mass, the influence of different height-to-diameter ratios on rock mechanics and acoustic emission characteristics was studied by using PFC2D software. The damage constitutive model of rock was established, and the damage evolution characteristics of rock with different height-to-diameter ratios were further analyzed. The results showed that, with the increase of height-to-diameter ratio K, the uniaxial compressive strength and peak strain of rock exhibited a gradual decrease; however, the elastic modulus gradually increased. Moreover, rock failure modes exhibited different characteristics under different K values. The scale effect showed little influence on the acoustic emission characteristics in the elastic stage; nonetheless, in the plastic deformation s tage and the residual damage stage, with the increase of the rock's height-to-diameter ratio, the maximum number of impacts of acoustic emission increased, the range of strong strain of acoustic emission decreased, and the maximum time of acoustic emission impacts increased gradually. The height-to-diameter ratio of the rock slightly influenced the zero-damage stage of the rock, but the damage affecting the rock increased slowly and accelerated the development stage. The damage evolution law was found to be similar when the K values varied from 1.0 to 2.0; however, when the K was greater than 2.0, the damage evolution law exhibited the characteristics of slowing down in the acceleration phase.
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