## 4 Features of AE Time Series for Rock Fracture under the Effect of Blasting  
The results of a representative sample were selected for analysis in each test scheme and the selected samples are separately labelled N1-1, N2-3, N3-1, and N4-2. The changes of the hit rate and cumulative AE hits monitored with time were extracted and the number of AE signals was counted based on a time interval of 1 s (Figure 3). Figure 3: _Cont._  
Figure 3 shows that the features of AE time series in different stress loading schemes were similar. The pores and fractures in the samples are gradually compacted and closed in the initial stages of loading. With increasing stress, the samples undergo stable crack propagation and the compacted primary cracks start to extend, accompanied by the initiation of new cracks. As the load increases, the samples enter the unstable crack propagation stage, during which numerous new cracks are generated, these then propagate and coalesce. In this case, the AE activity is further intensified. The stable and unstable crack propagation stages are the main stages of initiation and propagation of cracks in the samples. Much elasto-plastic strain energy is accumulated in the stages before blasting. The blasting is performed after the AE activity tends to stabilise when the stress is applied to the designed target value. After blasting, AE hits abruptly rise, and the cumulative AE hits suddenly increase. The stress field in the samples is constantly adjusted and internal cracks and fractures gradually propagate and coalesce due to the blasting-induced disturbance in this high-stress environment, thus, many AE events occur after blasting. The regional stress recovers, then stabilises and the AE activity decreases over time. The attenuation time of the AE activity increases with the increasing number of blasting operations. As a result, the overall stability of the samples declines and the probability of triggering failure of the samples grows. In the later stages of the loading process, many new cracks are initiated in the samples and new and primary cracks further propagate, accumulate, and coalesce, causing the sample to undergo macroscopic failure. With the increase of stress, the samples enters the crack stability and unstable growth stage, and the attenuation time of acoustic emission events increases gradually. The attenuation time after the last blasting is the longest. The shortest and longest acoustic emission attenuation time of model N1-1 after single blasting are 200 s and 500 s respectively, while the shortest and longest acoustic emission attenuation time of model N4-2 are 80 s and 400 s respectively. The higher the stress level of the model, the longer the shortest and longest acoustic emission attenuation time of the model after single blasting. When the explosive was detonated, a very large amount of energy was rapidly released, causing a strong disturbance within the specimen. The stress inside the specimen was adjusted and concentrated in some regions, causing the initiation and expansion of a large number of microcracks. After blasting, the stress returned to a relatively balanced state, and the AE activities rapidly weakened. Dislocation theory states that when the displacements at both ends of a slip surface are not uniform because of the inhomogeneity of the specimen, residual stresses are formed that lead to the generation of some new microcracks. Therefore, AE activities continue for a certain period before returning to a peaceful state. Both stress loading and blasting disturbance will cause damage and destruction in the specimen. According to statistics, for N1-1 sample, the proportion of AE signals generated by stress loading and blasting disturbance is 78.23% and 21.77% respectively. For N2-3  
Figure 3: AE time series features. (**a**) N1–1; (**b**) N2–3; (**c**) N3–1; (**d**) N4–2. sample, the proportion of AE signals generated by stress loading and blasting disturbance is 81.21% and 18.79% respectively.