# Simulation Tests on Granite Pillar Rockburst
## 3 Test Results and Analyses
### Analysis of Acoustic Emission  
Even though the rockburst video and the stress-strain measurement system of the testing apparatus can observe the macroscopic damage relationship of the test from the calm period to the occurrence of the rockburst, the damage process inside the specimen is difficult to reflect. However, with the aid of an acoustic emission system, the internal damage law of the rock can be accurately represented [38; 39]. In this section, we investigate the pillar's rockburst process by assessing the number of events and the energy evolution law of acoustic emission, analyzing the rockburst stage information and establishing whether or not the test rock is in a rupture state. As shown in Figures 6 and 7, the event rate and energy rate of the acoustic emission test periodically increase and subsequently decline, revealing a multi-peak condition. The total number of acoustic emission events and cumulative energy grow gradually, reflecting the damage form, damage state, and damage degree at various stages of the rockburst process.  
When exposed to uniaxial compression, rocks can be split into five stages, according to [PERSON]'s definition of stress-strain curves of rocks under compression: crack closure stage (I), linear elastic deformation stage (II), crack initiation and stable extension stage (III), unstable extension of the crack stage (IV), and destruction and post-peak stage (V) [40; 41]. Each of these two stages is separated by a distinct stress value associated with crack evolution, with stress levels corresponding to crack closure stress \(\sigma_{cc}\), initiation stress \(\sigma_{ci}\), damage stress \(\sigma_{cd}\), and peak stress \(\sigma_{c}\). In this study, we utilize the volumetric strain method  
Figure 5: Cloud image of a rockburst strain field (Black circles indicate areas of maximum strain).  
to calculate the typical stresses for each of the two phases, which are 24.3 MPa, 39.5 MPa, 53.1 MPa, and 70.83 MPa [42].  
Using the example of Figures 6 and 7, stage I denotes the gradual closure of the specimen's original cracks, porosity, and other flaws under external strain. At this point, only the specimen's surface is distorted to generate microcracks, resulting in a limited number of acoustic emission events and a gradual rise in the total energy of the emissions. New cracks begin to form and spread throughout the specimen as the loading increases in stages II and III. This causes a gradual increase in the number of acoustic emission events and multiple peaks of acoustic emission events, as well as a steady and continuous rise in the total energy of acoustic emission events. In stage IV, stress loading causes the specimen's crack and fracture structure surfaces to rapidly expand. As a result of the quick crack formation, the number of acoustic emission events quickly approaches the maximum value, and the energy rate also sharply approaches the maximum value. The specimen's number of acoustic emission events and energy rate have reached their maximum values in stage V, and the specimen's cumulative number of events and cumulative energy have also reached their maximum values. At this point, the specimen's rockburst phenomenon occurs, and the original stored energy is fully released.