# 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
### Selection of Mining Methods and Technical Adaptability Analysis
#### 2.2.3. Backfilling Mining Method  
The backfilling mining method improves the stability of surrounding rock and controls surface subsidence by filling mined-out areas with cemented tailings, slurry, or solid waste. This method ensures both the safety and environmental sustainability of mining operations [30]. With the advancing green mining policies, the use of backfilling methods has become more widespread in both metallic and non-metallic mines. Various forms have emerged, such as cemented tailings backfilling, slurry backfilling, and strip-style backfilling, to accommodate diverse mining requirements [31]. For example, the Jinfeng Gold Mine [32] utilizes an upward access cemented backfilling method, which significantly increases ore recovery and reduces surface disturbance and collapse risks, highlighting the dual benefits of this approach in enhancing mining efficiency and protecting the environment.  
In the context of green mine development, numerous scholars have explored backfilling mining technologies. [PERSON] et al. [31] examined the application of green backfilling technologies and analyzed their effectiveness in a coal mine working face. [PERSON] et al. [33] argued that backfilling is an effective solution to environmental and safety challenges in mining and serves as a key technology for green mining. [PERSON] et al. [34] further asserted that backfilling mining not only maximizes mineral recovery but also protectsunderground and surface environments, aligning with sustainable development goals. In terms of engineering practice, [PERSON] [35] proposed a composite backfilling scheme for gently inclined phosphate ores--\"pseudo-inclined segmented strip backfilling + upward horizontal layered backfilling\"--which has demonstrated stability across varying depths and structural conditions. This further confirms the potential of backfilling methods in mining applications.  
Importantly, recent policy documents, such as the \"Green Mining Guidelines for Non-Coal Mines\" and the \"14 th Five-Year Plan for Mining Safety Production,\" explicitly state that \"new mines should prioritize the use of backfilling methods,\" thereby promoting the standardization and institutionalization of this technology [36]. The backfilling mining method's unique advantages in reducing tailings discharge, optimizing waste utilization, and protecting surface ecology position it as a critical technological enabler of green, safe, and efficient mining practices.  
A comparative analysis reveals that the backfilling method is the most effective in most open-pit to underground mining operations, demonstrating high safety, high resource recovery rates, and minimal ecological impact. Consequently, it is emerging as the preferred choice driven by policy. The slope method is suitable for rapid development in stable areas and offers economic advantages. The caving method is effective for releasing large-scale resources; however, its application is restricted, and it carries significant risks. Mining methods should be systematically assessed based on factors such as orebody geometry, rock mass structure, hydrogeological conditions, and slope stability. These factors should be integrated with construction schedules, economic feasibility, and environmental objectives to develop a zoned, phased strategy. It is recommended that 3D modeling, GIS [37], and intelligent decision-support systems be incorporated to enhance the scientific basis of method selection and improve dynamic adjustment capabilities [38]. Overall, the selection of an appropriate mining method not only influences resource utilization efficiency and operational safety but also plays a crucial role in determining the sustainability of the transition. In the context of green development, the backfilling method, with its high adaptability and environmental benefits, is increasingly becoming the dominant technology for transitioning from open-pit to underground mining, providing a replicable and scalable model for the mining industry's transformation.