Mechanism of rockburst occurring in protected coal seam induced by coal pillar of protective coal seam

The rockburst accidents in Changchengyi Coal Mine and Junde Coal Mine show that high abutment stress exists in the affected area of the pillar of the protective seam, and that hard roof exists above the longwall panel. By comparing the occurrence conditions of the two accidents, the main factors causing the rockburst accidents in the protected coal seam are analyzed. The results indicate that due to the coal pillar of the protective seam, two types of rockburst accidents may be induced. (1) With a large burial depth and small seam distance, the accident is induced by high static stress (the main factor) and low dynamic stress (the minor factor). (2) With a medium burial depth and large seam distance, the accident is induced by high dynamic stress (the main factor) and low static stress (the minor factor). The static stress (mainly affected by burial depth) is mainly composed of the transfer stress resulting from the coal pillar, and the self-weight stress caused by the strata between the two seams, and the residual abutment stress of the gob that is situated on the same level with the protective coal seam. The dynamic stress is mainly the lateral abutment stress of the gob that lies on the same level with the protected coal seam. In addition, the evaluation method for rockburst is established, and it may provide a theoretical basis for mines with similar geological conditions. Finally, some treatment measures, such as design of the position of the longwall panel, rational arrangement of roadways, stress pre-releasing and enhancement of monitoring, are proposed.