# Failure Mechanism of the Yizhuxiang Collapse under the Joint Effect of Freeze-Thaw and Mining
## 5 Conclusions  
Under the effects of mining and precipitation, the rock mass Yizhuxiang underwent continuous deformation in 2015, and the top rock mass was bent and toppled, and master fractures and four dominant joints were formed in the rock mass. In 2022, the extremely cold weather led to the overall failure of the rock mass Yizhuxiang, which damaged the farmland, the temporary cement mixing station, and the road at the slope toe. The Yizhuxiang collapse had multiple causes, including mining, precipitation, and geological conditions.  
1. Geological structure: the rock mass Yizhuxiang had three free faces. The stratum was dominated by brittle dolomite, hard at the top and soft at the bottom. The studied area experienced frequent and considerable precipitation and strong weathering. Water flowing into the rock fractures increased the static and dynamic water pressure on the rock mass, and increased the lateral pressure on the free faces of the rock mass, which was not conducive to the stability of the rock mass;
2. External disturbance: The mining of phosphate ores at the bottom of the studied area was stopped in July 2014, and the safety pillars remaining at the lower part of the rock mass continued to be deformed, accelerating the deformation of the upper rock mass and the expansion of fractures. Continuous precipitation increased the water content of the stratum, and the joint action of seepage softening and pore pressure caused the cracks and joints to go deeper and become wider, and gradually penetrate downward. In 2015, the deep-hole blasting of the perilous top of the rock mass Yizhuxiang also caused fatigue damage to the rock mass. The cumulative effect gradually caused the looseness of the structural plane of the rock mass and reduced the strength of the rock mass;  
Figure 10: Evolution process of Yizhuxiang collapse; (**a**) Fracture formation stage; (**b**) Rear edge fracture formation stage; (**c**) Collapse formation stage; (**d**) Fracture penetration stage.  
* Freeze-thaw effect: from January to February 2022, Yuan'an County had a low average temperature and a snowfall much deeper than those in previous years. The effect of freeze-thaw became the main factor finally inducing the collapse. The collapse caused by freezing and thawing is caused by the frost-heaving force generated by water. When dealing with a collapse disaster caused by freezing and thawing, the salinity of surface water can be changed to reduce the freezing point of water.  
Collapses caused by freezing and thawing can also occur in areas with low latitudes, low altitudes, and warm and humid climates, which has played a role in improving the prevention and control of collapses in low latitudes and low altitudes.  
Conceptualization, W.H. and C.Z.; Methodology, S.H.; Validation, W.H.; Investigation, H.X., D.A. and L.K.; Resources, J.Y.; Data curation, H.X.; Writing--review & editing, S.H., Y.H. and C.Z.; Visualization, W.H.; Supervision, S.H.; Project administration, S.H. and W.H.; Funding acquisition, C.Z. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the following 5 funds, programs, projects: Key R & D Program of Xinjiang Uygur Autonomous Region (2021B03004-3), The Natural Science Foundation of Jiangsu Province (BK20221126), National Natural Science Foundation of China (42207169), China Postdoctoral Science Foundation (2022M710177), The Seventh Geological Brigade of Hubei Geological Bureau science and technology project (DQKJ2022-1, DQKJ2022-2).  
Not applicable.  
The data presented in this study are available on request from the lead author.  
The authors declare that they have no known competing financial interest or personal relationship that could have appeared to influence the work reported in this paper.