# Study of the Internal Rebreaking Characteristics of Crushed Gangue in Mine Goal during Compression
## 5 Conclusions  
1. Under the condition of confined compression, the change curve of the axial strain of the crushed gangue sample in the caved zone with time showed a straight upward trend at the beginning of the test, which increased with time, showing a sharp rise at first before slowing at the end. The softer the lithology, the greater the initial rate of growth, and the greater the final strain value reached at the end of the test.
2. The stress-strain curves of crushed gangues with different lithologies in the caved zone showed nonlinear growth. The difference was that the lower the strength of the gangue sample, the slower the initial rise of the curve, and the greater the final strain. The stress-strain curves showed typical characteristics, which were divided into the rapid compaction stage, slow compaction stage, and stable compaction stage. The strain of the combined samples were somewhere between those of the individual samples.
3. In confined compression, the AE characteristics of crushed gangue were different at different deformation stages. Based on the AE test, the compaction process was divided into the sliding flow deformation stage, fracturing deformation filling stage, and compaction elastic deformation stage, corresponding to the stress and strain in the compression of the samples. The failures of the large particle skeleton, the sliding flow of medium particles, and the filling of pores by small particles were the main reasons for the compression deformation of crushed gangue samples, respectively.
4. There was a positive correlation between the fractal dimension and the proportion of gangue samples with singular and combined lithologies, with the fitting degree above 0.98. Based on the compaction characteristics of crushed gangue samples and AE tests, the crushing stage characteristics of crushed gangue during compaction were summarized.  
**Author Contributions:** Conceptualization, P.W., W.G. and W.Y.; methodology, W.G., E.B. and W.Y.; software, P.W., W.Y. and S.H.; validation, P.W. and W.G.; formal analysis, P.W. and W.Y.; investigation, P.W. and S.H.; data curation, P.W. and S.H.; writing--original draft preparation, P.W. and W.Y., writing--review and editing, P.W., W.G. and W.Y.; supervision, W.G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Key Project of the National Natural Science Foundation of China (U21A20108, U1810203); the National Natural Science Foundation of China (52104127, 52174108, 51974105); the Henan Science and Technology Research Project (212102310399, 222102320058); the Project of Science and Technology Innovation Leading Talent in Central Plains (24200510012); the Henan Excellent Youth Science Foundation (222300420045); the Program for Science & Technology Innovation Talents in Universities of Henan Province (21 HASTIT024): the scientific and technological innovation research team of Henan Polytechnic University (T2021-5); the Key Scientific Research Projects of Colleges and Universities in Henan Province (21A440003); and the Research fund of Henan Key Laboratory for Green and Efficient Mining & Comprehensive Utilization of Mineral Resources (Henan Polytechnic University) (KCF202002).  
**Infrared Consent Statement:** Not applicable.  
**Data Availability Statement:** The data used to support the findings of this study are included within the article.  
This research was financially supported by the contents in the fundings. The authors thank the anonymous reviewers for their careful work and thoughtful suggestions that helped improve this paper substantially.  
The authors declare no conflicts of interest.