At present, in a longwall mining process, a 121 mining method, that is, one working face needs to excavate two roadways firstly and retains one coal pillar for supporting, is employed. In this structure, the coal pillar is required to be retained to cause large waste of resources. And, each working face needs to excavate two roadways to lead to low work efficiency.
In order to save coal resources, non-pillar mining technique is gradually put into practice. However, when the non-pillar mining is used, due to characteristics of a longwall beam roof pressure, periodic pressure will be generated. The periodic pressure not only has great pressure but also creates extremely huge destructing force to the coal mining working face, and even causes coalmine accident.
USPTO Backgrounds
USPTO Backgrounds