Research on bolting with difference scale in composite layer of roadway roof

The study focuses on the combination of bolting with different scale to solve the disadvantages in composite layer of roadway roof.FLAC^3D has been applied to analyzing the research which including seven combinations.The results show the long bolting can control displacement and stress distribution，and the short bolting can prevent from sliding.The new method can meet the expected requirement to compare with the old，and DCC is closest to the original results.The mechanism of bolt with different length has been speculated.This paper is of great significance in application of the bolting in the future.