# Research Progress and Typical Case of Open-Pit to Underground Mining in China
## 2 Analysis of Key Technologies for the Transition from Open-Pit to Underground Mining
### Current Status of Slope Stability Research in Open-Pit Underground Mining
[50] employed a three-dimensional difference element code to investigate the role of the movement release mechanism in planar transitional slope failure, emphasizing how the geometry of different discontinuity sets impacts the three-dimensional block shape and volume of unstable rock masses, thus delivering more precise simulation data for slope stability studies. [PERSON]. [51] used the Shizhuyuan nonferrous metal mine as a case study and applied the true three-dimensional safety analysis method to evaluate the safety and stability of mine slopes. The model's overall results reveal only minor tensile damage (Figure 4a). The compressive and tensile stresses experienced by the open-pit mine remain within the safe range (Figure 4b); the Z-direction displacement shows that the high point of the model settles while the low point rebounds, with no penetration of the plastic zone (Figure 4c), and the model monitoring simulation shows that displacement at monitoring points fluctuates initially before stabilizing (Figure 4d), indicating that the slope ultimately reaches a stable state, thus confirming the effectiveness of the slope stability control plan. Despite significant advancements in both theoretical and technical aspects of slope stability research, several challenges persist. On the one hand, a unified theoretical framework for slope instability mechanisms in open-pit and underground combined mining remains to be established, especially in complex geological conditions such as high-stress zones, multiple fault zones, and weak interlayers, where research on the response characteristics of rock masses remains underdeveloped. On the other hand, although existing numerical models demonstrate high theoretical accuracy, they face limitations in param sensitivity and generalizability, and their applicability to engineering practice requires further enhancement. Future research should progress along three collaborative paths: first, the development of a multi-field coupling analysis model that integrates stress disturbances, hydrogeological variations, and structural evolution; second, the advancement of slope instability prediction methods using machine learning and graph neural networks; and third, the creation of a dynamic feedback system that combines real-time monitoring with model simulations to improve the responsiveness and adaptability of early warning systems. Additionally, in line with the principles of green mining, efforts should focus on the synergistic optimization of slope protection and resource recovery to achieve an integrated approach to safety, efficiency, and ecology. Research and Technical Risk Analysis of Crown Pillar Thickness in the Transition from Open-Pit to Underground Mining  
As the depth of open-pit mining increases, the mining challenges and economic-technical constraints become more pronounced. To ensure the continuous operation of the mine, it is generally necessary to transition to underground mining once the critical depth is reached. However, the slopes formed during open-pit mining, when subjected to the synergistic effects of underground mining, may create significant safety hazards. Specifically, if these hazards are not properly addressed, they could lead to major incidents such as open-pit slope collapse, instability in underground mining areas, or flooding of underground workings caused by surface water accumulation [52]. Consequently, a certain thickness of crown pillars is typically left between the open-pit and underground mining areas to ensure safe and coordinated operations. Figure 4: Three-dimensional model and stress analysis of open-pit mining (adapted from [PERSON] [51]): (**a**) three-dimensional model of the final realm of open-pit mining; (**b**) maximum principal stress diagram; (**c**) Z-directional displacement diagram of the overall model; (**d**) the locations of the open-pit boundary slope displacement monitoring points. 2.4.1.