# New Perspectives on Excavation Disturbance Zones: Main Driving Forces
## 6 Conclusions  
Considering environmental factors (such as humidity and temperature), the formation process and internal mechanism of the EDZ after tunnel excavation under different working conditions were comprehensively studied using a self-developed RFPA\({}^{\text{2D}}\) code, which introduced numerical algorithms for the humidity-stress-damage coupling model or thermo-mechanical coupling model with damage evolution. The main conclusions drawn from this study are as follows:  
1. Under no-load conditions, an EDZ is formed, which expands gradually along with the propagation of environmental factors in the rock mass. Therefore, environmental factors are the driving forces for the formation of the EDZ.
2. Under no-load conditions, the rock mass in the EDZ is mainly dominated by the deterioration of the material properties and is accompanied by slight damage. Under load conditions, the rock mass in the EDZ is destroyed in a large area; furthermore, the speed and extent of damage are significantly larger than those under no-load conditions, and the depth of the EDZ is significantly larger than that under no-load conditions. However, in the case of the isolation of environmental factors, the depth of the EDZ and the damage extent of the rock mass are significantly reduced. Thisconfirms that environmental factors are the main driving forces for the formation of the EDZ (this is the new perspective on EDZs, as obtained in this study).
3. The deterioration of the rock mass material properties caused by the propagation of environmental factors in the rock mass is found to be a process related to time and space, from which the time-dependent properties of the EDZ originate. Under a low confining pressure or even without confining pressure, the deterioration of the rock mass material properties, related stress fields, and additional deformation caused by environmental factors are the fundamental causes for the formation of the EDZ.
4. The numerical simulation method considering environmental factors accurately reproduced the EDZ phenomenon, which was in good agreement with the actual on-site conditions, thus revealing the internal mechanism of the formation of the EDZ. The findings provide a theoretical basis for the further development of the support theory of the EDZ. Furthermore, several phenomena that could not be explained by the existing support theory of the EDZ were determined individually in this study, which provides a new idea for future research on EDZs.  
Methodology, X.K., S.W. and C.T.; validation, C.Y. and S.W.; resources, C.T. and X.C.; organization of data, Z.S.; writing--original draft preparation, X.K.; writing--review and editing, C.Y., X.C. and Z.S.; supervision, C.T. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (NSFC) (Grant No. 41941018), the Chinese National Natural Science Foundation (Grant No. 51627804), the National Natural Science Foundation of China (Grant No. 42107208), and the Sichuan Science and Technology Program (Grant No. 2021Y0394).  
Not applicable.  
The authors thank the anonymous reviewers, who provided valuable suggestions that improved the manuscript.  
The authors declare no conflict of interest.