# Percolation Threshold of Red-Bed Soft Rock during Damage and Destruction
## 4 Conclusions  
At present, the theory and experimental research of percolation in soft rock is insufficient. The experimental determination of the percolation threshold and effective quantitative description of damage in soft rock have yet to be fully developed. Further, the influencing factors on the percolation threshold of red-bed soft rock are not clear or understood. In view of this, percolation in the process of damage and destruction of red-bed soft rock was studied in this paper by taking red-bed soft rock as the research object of theoretical analysis, compression testing and numerical simulation. The damage characteristics of soft rock were analyzed, the percolation threshold of soft rock under different conditions calculated, and the essential law of percolation of red-bed soft rock revealed. The main conclusions are as follows:  
1. The feasibility of carrying out damage and destruction research on red-bed soft rock, based on percolation theory has been established. Based on microstructural analysis of typical red-bed soft rock, the model of the soft rock renormalization group can be constructed. The constitutive model of percolation damage and a method of calculating the percolation threshold of red-bed soft rock under different compression conditions is presented.
2. According to percolation theory, red-bed soft rock damage is quantitatively determined using AE measurement. Through AE tests of uniaxial compression of red-bed soft rock, the compression process of red-bed soft rock is revealed as having five stages of damage: initial damage, stable development of damage, sharp damage, peak damage, and residual damage. According to the constitutive model of percolation damage established in this paper, the average percolation threshold of red-bed soft rock is first obtained experimentally, and the rationality of the theoretical percolation threshold obtained by renormalization group theory is then verified.
3. The numerical simulation of percolation in red-bed soft rock as described in this paper has been executed well. Based on this, the percolation of red-bed soft rock under conventional triaxial compression and water-stress coupled triaxial compression were simulated. The influence of confining pressure and water on the percolation threshold of red-bed soft rock is then obtained. The results show that the percolation threshold increases with an increase in confining pressure, but decreases significantly after rock-water interaction.  
L.Y.: investigation, visualization, writing-original draft, writing-review & editing. H.L.: investigation, visualization, writing-original draft. C.Z.: conceptualization, methodology, formal analysis, supervision, resources, validation. Z.L.: conceptualization, methodology, formal analysis, supervision, resources, validation. L.Z.: writing-original draft & editing, formal analysis. All authors have read and agreed to the published version of the manuscript.  
National Natural Science Foundation of China (41977230); Major Project with Special Fund for Applied Science and Technology Research and Development in Guangdong Province, China: (2015b090925016); Major Project with Special Fund for Applied Science and Technology Research and Development in Guangdong Province, China (2016B010124007).  
All data used during the study appear in the submitted article.  
**Acknowledgments:** This work was supported by the National Natural Science Foundation of China (41977230); Major Project with Special Fund for Applied Science and Technology Research and Development in Guangdong Province, China (2015b090925016); Major Project with Special Fund for Applied Science and Technology Research and Development in Guangdong Province, China (2016B010124007).  
**Conflicts of Interest:** The authors declare that they have no conflict of interest.