Recognition of coal and gangue (roof rock) is a key technology to realize fully mechanized top coal caving automated mining. This paper proposes to detect the instantaneous refuse content of drawn coal and gangue mixture during top coal caving by using natural gamma-ray technology. The generating environment of coal and rock seams, the distribution characteristics of natural gamma ray from coal and roof-rock and the principle of coal-gangue recognition using natural gamma-ray method were analyzed. The natural gamma ray radiation characteristics of coal and roof-rock seams from seven different typical coal mine areas who has thick coal seams in China have been researched, and a connection between radiation intensity and refuse content was set up. The experiments on the mixed condition of roof-rock drawn from caving opening in the caving process of fully-mechanized top coal caving working face was taken and the radiative signals was real-time detected by using the self-developed coal-gangue recognition experimental system. The experiments results demonstrate the feasibility of using natural gamma-ray technology to perform real-time detection of refuse content of drawn coal and gangue mixture and the availability of self-developed coal-gangue recognition detector.

In extra-thick coal seams, mining operations can lead to large-scale disturbances, complex overburden structures, and frequent and strong strata behavior in the stope, which are serious threats to mine safety. This study analyzed the overburden structure and strata behavior and proposed the technique of confined blasting in water-filled deep holes as a measure to prevent strong rock pressure. It found that there are two primary reasons for the high effectiveness of the proposed technique in presplitting hard coal and rock. First, the fracture water enables much more efficient transfer of dynamic load due to its incompressibility. Second, the subsequent expansion of water can further split the rock by compression. A mechanical model was used to reveal how the process of confined blasting in water-filled deep holes presplit roof. Moreover, practical implementation of this technique was found to improve the structure of hard, thick roof and prevent strong rock pressure, demonstrating its effectiveness in roof control.