# Underground Disposal of Coal Gauge Backfill in China
## 5 Problems and Proposed Solutions
### Prospects
#### 5.2.2 Research and Development of New Equipment  
(1) Optimized design of the backfilling shield  
The up-to-date high-efficiency backfilling mining should dispose of a large amount of coal gangue without affecting the coal mining. One significant change to the backfilling shield in response to this demand is removing the compactor. There has been a trend towards a compact structural design of backfilling shields to reduce the size, improve the space utilization rate, and support the efficiency of the shields. Specifically, the relative position between the four-bar linkage dimension, the linkage, and the post are optimized to achieve a compact spatial layout. The design of the working space under backfilling reduces the amount of ineffective space and achieves compact, safe, and effective goals. The length of the front and rear top beams is optimized so that the support better accommodates the roof deformation. The supporting line is moved backward to the tail of the top beam to accommodate roof caving and improve the coal mining and backfilling efficiency [101; 102; 103]. (2) Research and development of a novel type of multihole-bottom-dump chain conveyor  
The following aspects of the multihole-bottom-dump chain conveyor should be optimized to achieve the high-efficiency, fixed-point, and quantitative unloading of the filling materials, which includes: the gradation of coal gangue; the hanging method of the multihole-bottom-dump chain conveyor; the method of connection between the scrapers; strength of key components; and the position, size, and switch mode of the dumping hole [104; 105].  
As shown in Figure 7, a hydraulic cylinder can be used to hang the multihole-bottom-dump chain conveyor. By changing the original hanging method, one can avoid bending and compression of the multihole-bottom-dump chain conveyor and improve its reliability. The conveyor's central double chain design is changed to a side double chain, increasing the dumping area of the dumping hole. The conventional rectangular shape of the dumping hole is changed to a shape consisting of a rectangle and a semicircle. An arched connection is adopted between the flashboard and scraper of the dumping hole to avoid height difference and prevent clogging by the coal gangue. The multihole-bottom-dump chain conveyor's preferred transport capacity is 1000 t/h and above, as required by the high-efficiency large-scale gangue disposal technology.  
Figure 6: Schematic diagram of high-efficiency gangue backfilling technologies.  
(3)  
Research and development of the gangue pipeline pumping system  
Slurry backfilling in the goat requires that the pipeline pumping system should have the desired transport performance for coal gangue and water over long distances without clogging. To meet this demand, one should further optimize the gangue-based slurry's mix ratio for backfilling to ensure favorable rheological properties, a low bleeding rate, a uniform composition, and the convenience of pipeline transportation of slurry. During the transport, the pumping system's capacity should be improved to accommodate a long distance by adding a smooth coating inside the transporting pipeline and by increasing the pumping power, to facilitate the continuous transport of coal gangue, and the backfilling of the goat. Moreover, the stop's spatial distribution can be accurately determined by numerical simulation or surveying to make preliminary decisions concerning the laying of the pipeline pumping system.