# Calibration Method of PFC3D Micro-Parameters under Impact Load
## 5 Conclusions  
Based on the SHPB test method and the FLAC3D/PFC3D numerical method, a continuous-discontinuous (FLAC3D/PFC3D) coupled SHPB numerical test model was established in this study. The quantitative relationship between the macroscopic physical and mechanical parameters and the microscopic parameters of SJM was determined and verified through many numerical tests. Finally, a calibration method for the micro-parameters of SJM under impact load is proposed, and the main conclusions are as follows:  
1. Laboratory static physical and mechanical tests and SHPB tests were carried out on limestone samples to determine the macroscopic physical and mechanical parameters of the rock samples. At the same time, based on the SHPB laboratory test and the FLAC3D/PFC3D bridge domain coupling method, a continuous-discontinuous SHPB numerical test model is established.
2. Through univariate analysis, the influence between six micro-parameters of the numerical model and the macroscopic physical and mechanical parameters are explored,  
Figure 23: Comparison of failure modes.  
Figure 24: Micro-parameter calibration flow of SJM under impact load.  
and the microscopic parameters of SJM to be calibrated are simplified into three types, namely pb_deform emod \(\overline{E}_{c}\), pb_coh \(\overline{\sigma}_{c}\), and sj_kn \(\overline{k}_{n}\). Then, the quantitative relationships between the three micro-parameters and the three macro-physical and mechanical parameters were established by two-factor regression analysis.
3. The calibration process for the microscopic parameters of SJM under impact load was established, and the quantitative relationship between microscopic and macroscopic parameters was verified according to the SHPB test. The relative error of the macroscopic parameters between the numerical and laboratory tests is less than 5%, which shows that the proposed calibration method is more accurate and reliable than previous methods. At the same time, compared with the traditional calibration method of trial and error, the calibration efficiency of the micro-parameters is improved.
4. This paper provides a more reliable continuous-discontinuous numerical model for the SHPB test and also provides the calibration process for the model's microscopic parameters, which supplies a certain reference value for the study of the rock model under impact load. Due to the limited number of experiments conducted in this study, it is necessary to increase this number in the future to fully validate the calibration process.  
Methodology, Z.Z.; software, Y.K.; writing--original draft preparation, W.G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation of China, (Study on rock breaking process and mechanism of cutting blasting in deep high-stress rock roadway) grant number 51874189.  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to the privacy of the data.  
The support from [PERSON] and [PERSON] in the form of their guidance and assistance in the writing of this paper is gratefully acknowledged.  
The authors declare no conflict of interest.