## 3 Results
### Infrasonic Time Domain Characteristics  
Waveform analysis provides a comprehensive characterization of signal features in a complete picture, image and continuity. The background infrasonic signals and the test infrasonic signals are decomposed and reconstructed by the wavelet analysis and are combined with the time-mechanical parameters. The infrasonic time domain characteristics of the rock under cyclic loading and unloading are investigated and compared with the infrasonic time domain characteristics of uniaxial compression. Figure 7 shows the infrasonic time domain characteristics of the rock specimen A-1 under uniaxial compression. The horizontal axis shows the loading time (s), the left-hand side vertical axis shows the infrasonic amplitude (V), and the right-hand side vertical axis shows the axial stress (GPa). Figure 7 shows the infrasonic time domain feature of rock specimens under uniaxial compression, and the peak strength of rock specimen A-1 is 105.152 MPa. The variation in infrasonic amplitude before peak strength is significant. The axial stress at point A is 81.02 MPa (about 85% of the peak strength), and the infrasonic amplitude is 0.0047 V. The infrasonic amplitude during the elastic deformation stage of rock specimen. The infrasonic wave amplitude is low and stable, and the internal fracture in the rock is low. After point A, the variation in infrasonic amplitude is more significant, and when the rock specimen reaches the point of plastic deformation onset, the infrasonic amplitude gradually increases, indicating that microfractures begin to appear within the rock. At points B and C, the axial stresses were 99.69 MPa and 102.49 MPa, and the infrasonic amplitudes were 0.0071 V and 0.0051 V. Although the infrasonic amplitude at point C was not the highest, the infrasonic signals with higher amplitude were the most intensive, and the infrasonic amplitude reached a peak of 0.008 V when approaching peak strength, and the rock specimen undergoes rapid fracture propagation and coalescence. As shown in Figure 8, the peak strength of rock specimen A-4 is 84.502 MPa. In the low-stress stage of the first and second cycles, infrasonic amplitude demonstrates relatively stable variation characteristics, which is attributed to the fact that the rock is in the compaction stage. During this phase, pre-existing microcracks and pores within the rock gradually close, thereby resulting in nonlinear stress-strain behavior. In the initial loading stage, pre-existing microcracks and pores in the rock gradually close, leading to nonlinear stress-strain behavior, and the internal microfractures and micropores are compressed, resulting in a small amount of nascent fracture. With the increase in axial stress, the infrasonic amplitude shows a more obvious increase in the third and fourth cycle stages, such as at the upper limit stress of the third cycle at point A (437.2 s), the infrasonic amplitude is 0.006722 V, which is obviously higher than the previous infrasonic amplitude, and with the generation of new fractures, the infrasonic amplitude also changes accordingly. The amplitude of the infrasonic waves changes most significantly when entering the high-stress stage, especially in the fifth cycle stage, such as at the amplitude of 0.01142 V at point B (1125 s) of the fifth cycle loading stage. The amplitude of the infrasonic waves at point C (1280 s) after the fifth cycle of the upper limit stress reaches a maximum value of 0.0117 V. Point D of the fifth cyclic unloading stage (1387 s), with an amplitude of 0.008382 V, indicates that the internal fracture of the rock rapidly propagation, converges, and penetrates during the high-stress stage, and the mechanical properties deteriorate sharply. After point D and before peak strength, the infrasonic amplitude exhibits a state of low-magnitude stability with minimal fluctuation.