# Research Progress and Typical Case of Open-Pit to Underground Mining in China
## 3 Typical Case: Integrated Demonstration of Xinqiao Iron Mine
### Implementation of Mining Methods  
1. Block Layout and Structural Params:  
The ore chambers and pillars are alternately arranged along the strike of the ore body, with their lengths matching the horizontal thickness of the ore body. The ore chambers measure 14 m in width, while the pillars are 10 m wide. The bottom pillar height is 5 m, the top pillar height is 2 m, and the segment height is 9.9 m. Each segment is responsible for three layers, with each layer having a height of 3.3 m. During the mining process, the minimum roof management height is 3 m, and the maximum height is 6.3 m.
2. Mining Development Layout:  
The layout of the mining development is shown in Figure 9. It primarily consists of essential passageways for ore recovery, including the ramp, segmented haulage drifts, layered haulage routes, ore unloading crosscuts, chute shafts, and backfilling ventilation shafts.  
3. Mining Process:  
Rock drilling and blasting operations utilize the Boomer 281 drilling rig (as shown in Figure 10a), with a hole spacing of 1.3 m and a blast hole spacing of 1.1 m. The side-hole spacing is appropriately reduced, with the distance from the contour line of the mining area ranging from 0.8 m to 1.0 m, and the drill hole diameter is 42 mm.  
Figure 9: Schematic illustration of the upward horizontal layered backfilling mining method (modified from [PERSON] [23]): I-I shows the front view of the extraction method, II-II shows the left side view of the extraction method, and III-III shows the top view of the extraction method.  
4. Ore Removal:  
After each blasting and exhausting the fumes through adequate ventilation, the collapsed ore is transported by the diesel front loader through the haulage routes and segmented connecting drifts to the ore chute (as shown in Figure 10b). The loader's estimated capacity is 406.7 tons per shift. Given that the segmented ore volume is 11,400 tons, the net ore removal time is 29 shifts.  
5. Backfilling Process:  
The first-stage backfilling of the ore pillars, the first layer of ore chambers and pillars at the bottom, the crown backfilling, and the backfilling of each layer of ore chambers and pillars are performed using a binder material with a cement/fly ash/tailings mass ratio of 1:2:6, along with a binder concentration of approximately 70%. The second-stage backfilling utilizes a cement/fly ash/tailings mass ratio of 1:2:15, along with a binder concentration of approximately 70%. For crown backfilling, a sectional pressure-reduction method is applied to transport the backfilling material, where partition walls are constructed at the crown backfilling layer. The material is initially filled one to two times, and after the material settles and shrinks, additional backfilling is done to improve the crown backfilling ratio. The on-site backfilling process is illustrated in Figure 10c,d.  
6. Key Technical and Economic Indicators:  
Following the implementation of the upward horizontal layered cemented backfilling method, Xinqiao Mine achieves a recovery rate of 84.66% and a dilution rate of 3.41%. To further improve the recovery rate and reduce the dilution rate, measures such as  
Figure 10: Mining equipment and backfilling system at Xinqiao Mine: (**a**) boomer 281 rock drill dolly; (**b**) diesel front loader; (**c,d**) o-site layout of the Xinqiao Mine backfilling system. Source: Photographs by [PERSON].  
enhancing the quality of the backfilling, ensuring timely and stable backfilling maintenance, eliminating waste rock layers, and optimizing the mining process are recommended.  
Through the implementation of the mechanized upward horizontal layered cemented backfilling mining method, Xinqiao Mine effectively ensures the safety, efficiency, and relatively low dilution loss of underground mining operations. As open-pit mining concludes and the pit is closed, achieving ecological restoration of the open-pit area and the resource utilization of solid waste has become the final phase and a key demonstration of the green mining concept.