## 3 Results
### Damage Characteristics  
Acoustic Emission (AE) refers to the transient elastic wave phenomenon generated by the rapid release of energy in a medium. It can be used to evaluate the rate of crack propagation and the process of damage development in specimens. AE monitoring was conducted during uniaxial compression of specimens, yielding characteristics of AE variation with stress in the form of a curve [3]. The relationship between axial stress, AE event frequency, and cumulative AE counts is illustrated in Figure 5. Different coal-rock ratio specimens exhibit similar AE characteristics, which can be divided into four stages. In the initial loading stage, both AE event frequency and cumulative AE counts are relatively low. This is attributed to the presence of inherent cracks and pore structures within the coal body, leading to compaction of the specimen. During this stage, inherent cracks within the coal body continuously close, and concurrently, with the decrease in coal content, the cumulative AE counts for samples C, CSR (9:1), CSR (5:5), CSR (3:7), and R are 17,698; 17,105; 14,703; 11,759; and 8821, respectively, accounting for 0.8%, 1.26%, 1.56%, 1.22%, and 1.24% of the total cumulative AE counts, respectively. This indicates that a higher coal-rock ratio corresponds to more initial microcracks within the coal sample, resulting in a greater number of AE signals released during compaction. As axial stress increases, the specimen enters the stage of elastic deformation, during which AE activity relatively intensifies, and cumulative AE counts exhibit an approximately linear growth trend. In this stage, initial microcracks within the coal sample are further compacted, and a small amount of cracking occurs. When the axial stress reaches around 75% of the peak strength of the specimen, the specimen gradually enters the yielding stage of progressive failure. During this stage, AE events become active, the AE count curve shows a \"sudden change\" fluctuation, AE counts become denser, several peaks appear, and cumulative AE counts almost vertically rise and reach their maximum near the peak stress. Numerous new cracks develop within the specimen, indicating the onset of macroscopic cracking and failure characteristics, accompanied by brittle sounds. After reaching the peak failure stage, axial stress rapidly decreases, causing the specimen to lose its bearing capacity. Cracks within the specimen gradually expand, forming macroscopic larger cracks, leading to continuous surface damage. With an increase in the coal-rock ratio, the final cumulative AE counts of the specimens also increase continuously, and the AE characteristics of the specimens undergo corresponding changes. For specimens with relatively high coal content, such as C and CSR (9:1), multiple peaks in the AE event frequency occur near the peak stress, and cumulative AE counts show a stepwise increase. Overall, for specimens with coal-rock ratios of 0:10 (R), 3:7, 5:5, 9:1, and 10:0 (C), the cumulative AE counts are 7.09 \(\times\) 10\({}^{5}\), 1.07 \(\times\) 10\({}^{6}\), 1.31 \(\times\) 10\({}^{6}\), 1.35 \(\times\) 10\({}^{6}\), and 2.02 \(\times\) 10\({}^{6}\), respectively. Compared to the 0:10 (R) ratio, they increase by 50.92%, 84.77%, 90.41%, and 184.91%, respectively. This is because coal, as a special type of rock containing microcracks and micropores, generally has a much greater number of inherent cracks within its structure compared to rocks. The closure and sliding activity of internal cracks within coal are more frequent, leading to frequent AE activity. Therefore, with an increase in the coal component of the specimen, the number of AE count peaks increases, and cumulative AE counts also increase accordingly. Comparing the time-varying patterns of AE counts between the primary coal-rock combination CSR (5:5) and the artificial coal-rock combination CR (5:5), the cumulative AE counts are 7.09 \(\times\) 10\({}^{5}\), 1.07 \(\times\) 10\({}^{6}\), 1.31 \(\times\) 10\({}^{6}\), and 1.35 \(\times\) 10\({}^{6}\), respectively.