Determination on start-up area for floor rockburst at retained entry and its stepwise control technology

Entry floor usually suffers the greatest damage after floor rockburst. But the start-up area is not neces-sarily located within the floor. Based on the floor rockburst occurred at retained entry behind working face in a coal mine in Shanxi Province,the time and space sequences of rock burst associated with their corresponding relationship were ana- lyzed,and then the possible start-up area was pointed out. Numerical simulation code FLAC was utilized to analyze the load evolution law for the retained entry,and the “ relief channel” model within the floor was established. Based on field data,the key parameters for stepwise control technology for rockburst were determined,and on-site applications was carried out. The results showed that:“ relief channel” mechanism occurred within retained entry floor among the range of failure depth after the lateral coal was mined-out. The vertical stress in pillar increased,while the horizontal stress in the retained entry floor released through “ relief channel”. And the decline extent was positively correlated with the channel width. The elastic core area within pillar was start-up area for floor rockburst,and its increasing vertical stress was the leading load source. Due to the low strength of the floor,it became the main area where vibration en- ergy transformed to the crack surface energy and kinetic energy. In order to prevent start-up and mitigate the extent of damage of rockburst,the stepwise control technology was utilized,including the advanced pre-split within the hard roof,drilling within start-up area,setting drilling within cache corner to buffer shock,and non-asymmetric support at retained entry. After the application of technology above,the rock burst was successfully contained.