Non-coal pillar mining with roadway formed automatically (RFANM) is a new mining approach, which demonstrates revolutionary significance because it does not require making roadway before mining and coal pillar retaining. In order to explore the stability of the surrounding rock structure in RFANM, the deformation of the surrounding rock was theoretically analyzed and simulated based on three different fracture positions of the main roof. It was concluded that reasonable control of temporary support strength in roadway is of great importance to control the deformation of the entry. The deformation process of surrounding rock under different fracture positions in RFANM was simulated by using the Universal Discrete Element Code (UDEC). The results of the numerical simulation showed that the main roof was fractured at the solid coal side or gob side; the deformation of the roadway was small. The fracture condition of the main roof at the gob side required a higher effect of roof slitting or temporary support from the roadway. Through drilling and peeping at the retained roadway, it was judged that the main roof was broken inside the coal wall. Field monitoring results revealed that the deformation of the roadway can be effectively controlled.
This paper reports a simple and effective method to increase heating efficiency and forming temperature-sensitive materials during the hot forging process. In this study, a resistance type of equipment was set into the forging die and the billet was directly resistance heated through the forging die. On the basis of this innovative forming method, the heating effect for the billet appears to be the most dominant factor. The experimental result indicates that the billet could be heated quickly to 1000°C in about 5 seconds and the high-strength material was successfully formed to the shape of a bolthead. With this mechanism, the rapid heating and isothermal deformation during the hot forging process can be successfully achieved.
Presplitting cutting slots advance working face is the key technology of non—pillar gob—side entry retaining formed by roof cutting and pressure release. And the rationality of parameters not only affects the formation of the structural surface of joint-cutting, but also has a significant impact on the retaining roadway. In order to enrich and improve the system of presplitting cutting slots technology, this paper takes the 6302 working face in Baoshan Coal Mine as the research object to discuss the effect of presplitting cutting slots technology on the strata behavior law of the working face. Then the presplitting cutting height, cutting angle and the distance between blasting holes are determined as the key parameters based on theoretical calculation. And the working face hydraulic support monitoring data are analyzed statistically. The research shows that: when the cutting height, cutting angle and the distance between blasting holes is 5m, 15 °and 500 mm respectively, the structural surface of joint-cutting can form through cumulative blasting. The influence range of pre-splitting roof joint-cutting technology on underground pressure is 30m. Furthermore, the average holding power of the powered support decreased by 3.8mpa, and the first weighting interval and periodic weighting length of the roof respectively increased by 4m and 5.5m in the affected area.
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