## 4 Results and Discussion
### Breakage Rate of Broken Rock Mass in Different Size Grading Conditions  
AE is a phenomenon that spans the generation and propagation of acoustic waves caused by sudden irreversible changes in the internal structure of a material [42; 43; 44; 45]. In the discrete element model of broken rock mass, the basic element is \"ball', and the 'contact' between balls within a rock block is considered as parallel bonding. During the confined compression loading process of broken rock mass, bonding fractures occur, resulting in microcracks that are regarded as acoustic emission events. To better approximate real-time monitoring results of acoustic emissions, these occurrences of microcracks with similar initiation time and space are treated as individual AE events [46]. The total number of parallel bonding contacts in broken rock masses with different size grades cannot directly reflect the degree of secondary fracturing. Therefore, the concept of a microcrack ratio is introduced. The concept of a breakage ratio needs to be introduced, which can be defined as follows:  
\[R_{b}=\frac{n}{N} \tag{14}\]  
where \(n\) denotes the number of parallel bond fractures and \(N\) is the total parallel bonds in the broken rock mass model. The influence of impact-induced strength erosion on the AE events of broken rock mass and breakage rate with different size grading distributions was compared, and the results are shown in Figure 9.  
Figure 9: _Cont._  
According to Figure 9, impact-induced strength erosion has a significant effect on the increment of AE events in broken rock mass during the early stage of lateral compression loading overall. However, there is a small difference between them during the later stage of loading. This indicates that during the early stage of loading, microcrack propagation is mainly caused by the weakening effect of impacts from small-sized rock blocks. In contrast, during the later stage of loading, as voids decrease and impact particles are hindered and deposited, microcrack propagation induced by lateral compression in broken rock mass increases significantly compared to impact-induced strength erosion weakening effects. When the particle size distribution of the crushed rock masses is highly disparate, i.e., G3, the impact weakening effect has the greatest influence on the growth of microcracks and breakage rate in the broken rock mass. This is because larger rock blocks tend to fracture, while smaller ones are more likely to become impact particles under combined lateral compression loads and fluid forces. As G3 contains a higher proportion of both large and small particles, impact weakening occurs more frequently and thus exerts a greater influence. Conversely, when the particle size distribution of broken rock blocks is uniform, i.e., G1, the impact-induced strength erosion effect minimally influences secondary fracturing in the broken rock mass. The relationship between the breakage rate and strain of broken rock specimens with different size gradings under limiting constraints of compression and water immersion conditions, as calculated by using Equation (14), is shown in Figure 10.  
Figure 9: The evolution of the AE event increment and breakage rate. (**a**) AE event increment and breakage rate with size grading G1; (**b**) AE event increment and breakage rate with size grading G2; (**c**) AE event increment and breakage rate with size grading G3; (**d**) AE event increment and breakage rate with size grading G4; (**e**) AE event increment and breakage rate with size grading G5. As shown in Figure 10, the breakage rate-strain curve of broken rock mass is divided into three stages, corresponding to the stress-strain curve in Figure 8. In Stage I, deformation of the broken rock mass is predominantly induced by pore compression, and the rock mass skeleton structure is not yet stable, resulting in a minimal rock block failure rate. Combined with Figure 8, the breakage rate is closely related to the stress-strain curve pattern.