## 3 Results and Discussion
### The Stratification Effects of Rock's Splitting Characteristics
#### 3.1.2 Contribution of AE Characteristic Parameters  
The frequency characteristics of acoustic emission (AE) signals are crucial parameters for describing the rock rupture process. These characteristics are directly correlated with the fracture mechanisms of the seismic source. Ruptures of varying scales produce different peak frequencies: large-scale fractures generate signals with prominent low-frequency components, whereas small-scale fractures yield signals with dominant high-frequency components [34; 35; 36]. Additionally, the peak frequency is associated with the speed of crack propagation: a higher propagation speed results in a higher peak frequency, while a slower propagation speed results in a lower peak frequency. Consequently, peak frequency characteristics provide insights into the dynamic properties and mechanisms of crack propagation [29]. Figure 5 illustrates the temporal variation and distribution of AE peak frequency signals. For specimen 1-0-2, the peak frequency signals exhibit a distinct strip-like pattern, with a low-frequency concentration at 75-95 kHz and a high-frequency band at 260-310 kHz. Low-frequency signals predominate over high-frequency signals. High-frequency signals predominantly emerge during the later stages of loading. During the pre-loading phase, stress accumulates, crack propagation is slower, and energy release is more dispersed, resulting in a predominance of low-frequency signals. High-frequency signals, on the other hand, become more apparent in the later stages, when cracks rapidly propagate and extend. Based on the peak frequency distribution, high-frequency signals are significantly lower than low-frequency signals across the five different numbers of stratification layers. To further analyze the relationship between the stratification number and the proportion of high-frequency signals, the average proportion of high-frequency signals was calculated for 0-5 stratification layers at a stratification angle of 0\({}^{\circ}\), as shown in Figure 6. The proportion of high-frequency signals decreases exponentially with an increase in the number of stratification layers. This is mainly because of the high density and uniformity of intact sandstone, which facilitate small-scale fractures, resulting in a higher proportion of high-frequency signals. As the number of weak stratification planes increases, the number of large pores in the specimen also increases, leading to a higher probability of large-scale cracks. Additionally, under vertical loading, the crack propagation process is hindered by the stratification planes, and the high-frequency signals decrease, resulting in an increased proportion of low-frequency signals and decreasing the proportion of high-frequency signals. Figure 5: Specim peak frequency graphs: (**a**) specimen peak frequency varies with time and (**b**) peak frequency distribution. The variation in the proportion of high-frequency AE signals with the stratification angle is shown in Figure 7. As the stratification angle increases, the proportion of high-frequency AE signals initially rises and subsequently declines. Specifically, the proportion of high-frequency AE signals increases for stratification angles of 30\({}^{\circ}\), 45\({}^{\circ}\), and 60\({}^{\circ}\), with the average proportions reaching 34.52%, 38.165%, and 42.97%, respectively. When the angle between the loading direction and the bedding direction is small, crack propagation primarily follows the bedding direction. The rock exhibits strong structural coherence, limiting the initiation and expansion of cracks, resulting in lower-frequency acoustic emission (AE) signals. During this process, the deformation of the rock material is mainly dominated by shear and slow crack propagation, with fewer high-frequency components generated. As the angle increases to a certain range, the loading direction is no longer fully aligned with the bedding direction, causing greater resistance to crack propagation between the bedding planes, which induces new microcracks.