The effect of the dip angle of an interlayer coal seam on rock mass mechanical behavior and damage characteristics is seldom discussed. To address the lack of the existing research, a numerical simulation was conducted using the Particle Flow Code (PFC2D), and its damage to mechanical behavior, acoustic emission (AE)characteristics, and damage characteristics were analyzed. The outcomes exhibit the peak strength and elastic modulus of coal-rock combinations are between that of rock and coal. As the coal inclination angle rises, the elastic modulus and peak strength gradually decrease. AE model experiences the initial growth period, stable growth period, and rapid decline period. The value of AE hits and the generation of the AE signal is affected by the size of the inclination angle. The degree of damage to the coal-rock combination gradually rises as the angle rises. The damage process of the coal and rock composite sample encompasses an initial damage phase, damage stable evolution phase, accelerated damage phase, and a failure phase. The damage values of the stable evolution stage for varying dip angle models are also different. As the inclination angle increases, the damage value gradually increases, while the strain at the same damage value gradually decreases.

To better understand the effect of the size of hole defects on the mechanical properties of a rock mass, the two-dimensional particle flow discrete element code (PFC2D) is applied to establish rock mass models with single circular hole defects of different diameters. Uniaxial compressive strength (UCS) tests are conducted on each model by only taking the defect size (area) as a variable. This study analyzes each model’s stress-strain, contact force chain, crack evolution, meso-damage and failure, and mechanical properties. The results showed that with the size enlargement of the circular hole defects, each model’s UCS and elastic modulus gradually decrease, and the defect size is negatively correlated with the mechanical strength of the rock samples. The size of the hole defects affects the entire process of contact force chain and crack evolution. The larger the aperture dimension of the circular hole defects in each model, the greater the concentration degree of the contact force chain, the earlier the crack initiation, and the higher the degree of crack coalescence in the post-peak stage. The number of cracks decreases as the hole size increases, and the model is more prone to failure. Rock models’ strength and failure characteristics with different numbers and arrangements of hole defects are discussed under the same defect area condition.

To better understand the effect of the size of hole defects on the mechanical properties of a rock mass, the two-dimensional particle flow discrete element code (PFC2D) is used to establish rock mass models with single circular hole defects of different diameters. Taking the defect size (area) as the only variable, uniaxial compressive strength (UCS) tests are carried out on each model. The stress-strain, contact force chain, crack evolution, meso-damage and failure, and mechanical properties of each model are compared and analyzed. The results show that with the size enlargement of the circular hole defects, the UCS and elastic modulus of each model decrease gradually, and the defect size is negatively correlated with the mechanical strength of the rock samples. The size of the hole defects affects the entire process of contact force chain and crack evolution. The larger the aperture dimension of the circular hole defects in each model, the greater the concentration degree of the contact force chain, the earlier the crack initiation, and the higher the degree of crack penetration in post-peak stage. The number of cracks has a decreasing trend as the hole size increases, and the model is more prone to failure. Under the condition of the same defect area, the strength and failure characteristics of rock models with different numbers and arrangements of hole defects are compared and discussed.

The common occurrence of various number and distribution of hole flaws complicates the mechanical behavior and fracture mode of the rock masses that contain them. This study develops seven numerical models of limestone samples with different numbers and distributions of circular hole flaws using 2-D particle flow discrete element code (PFC2D) to investigate their impact on the mechanical properties of limestone while maintaining the same flaws area. In addition, it analyzes the effect of these factors on the mesomechanical features of each model, including the characteristic stress values (peak stress, crack initiation, and damage stress), crack evolution, stress, and displacement field. The results showed that the peak stress, crack initiation, and damage stress of the single-hole model are between those of multihole models. As the arrangement of dip angle increases, the peak stress, crack initiation, and damage stress of models with the same number of multihole flaws exhibit a V-shaped change. The characteristic stress values are the largest when the holes are vertically aligned. Model differences in crack development path, shape, and number, as well as stress concentration area and failure mode, are primarily due to the number and distribution of holes. The circular holes are arranged at approximately 45°, and the greater the number of defects, the more likely the model is to fail. The study’s findings can provide support and reference for the research system of deformation and failure of rock mass with hole flaws.