# Research Progress and Typical Case of Open-Pit to Underground Mining in China
## 1 Introduction  
After decades of intensive mining, most open-pit mines in China have transitioned into deep open-pit mining, facing a series of significant challenges. Firstly, as the mining area expands horizontally, available working space decreases, the width of working platforms narrows, and ore transportation distances increase. This reduces transportation efficiency, resulting in a decline in mining capacity and an increase in operational costs [1]. Secondly, as shallow resources deplete, open-pit mining continues to expand both vertically and horizontally, creating deep pits with steep slopes (as shown in Figure 1a,b). This not only increases technical complexity but also substantially reduces economic returns [2]. Thirdly, solid waste generated by open-pit mining accounts for more than 90% of the total stripping volume [3], leading to environmental pollution in the mining area (as shown in Figure 1c,d). This damages surface ecosystems, degrades working conditions, and results in a significant decline in labor productivity. In this context, the advantages of traditional open-pit mining, such as rapid production, low infrastructure investment, high safety factors, and minimal dilution losses, have gradually diminished [4]. Consequently, the traditional open-pitmining model is no longer sustainable, necessitating the transformation and upgrading of mining technologies. In this process, underground mining is emerging as a key approach for mineral resource development thanks to its superior resource recovery capacity and ecological adaptability [5]. Underground mining, characterized by precise development techniques and efficient extraction methods, can significantly reduce resource loss and enhance both the economic performance and safety of the mining system. From a policy perspective, the introduction of the \"Green Mining Standards for the Non-ferrous Metals Industry\" in 2018 marked the establishment of China's first national-level green mining construction standards [6]. These policies emphasize the adoption of environmentally friendly and efficient mining technologies to control surface disturbances and ecological damage. Underground mining avoids large-scale surface excavation and aligns with the core principles of green mining and sustainable development [7]. It should be particularly emphasized that the transition from open-pit to underground mining is not merely a change in production methods but a complex systems engineering process that demands comprehensive planning [8]. Open-pit and underground mining should be viewed as an integrated system, with safe and efficient operations achieved through scientific planning and coordination. Several key technical challenges must be addressed during this transformation: how to achieve spatial integration and functional transition between open-pit and underground systems, how to restructure the development system and select appropriate mining methods, how to control the stability of slopes and  
Figure 1: Environmental impacts of open-pit mining: (**a**) open deep concave pit; (**b**) open slopes and subsidence areas; (**c,d**) environmental pollution from quarries. Source: (**a,b**) adapted from [[[http://www.lyy.com.cn/1](http://www.lyy.com.cn/1)]([http://www.lyy.com.cn/1](http://www.lyy.com.cn/1)) (accessed on 9 July 2025); (**c**) adapted from [[[https://www.hangzhou.com.cn/index.htm](https://www.hangzhou.com.cn/index.htm)]([https://www.hangzhou.com.cn/index.htm](https://www.hangzhou.com.cn/index.htm)) (accessed on 9 July 2025); (**d**) adapted from [[[http://www.gyepchina.com/557/0/208](http://www.gyepchina.com/557/0/208)]([http://www.gyepchina.com/557/0/208](http://www.gyepchina.com/557/0/208))] (accessed on 9 July 2025). surrounding rock, and how to design crown pillars effectively to ensure operational safety and maximize resource recovery rates. These challenges are highly interconnected and mutually restrictive, placing higher demands on the overall planning of mining projects, technical integration, and intelligent management.