Abstract: To analyze the mechanism of different anchor beam arrangement, the 3D mechanical model of support system acting on roof was established, based on the research of strength in the post-peak region of surrounding rock under low confining pressure. And the confining pressure computing formulas of the roof under the independent action or combined action of bolts, anchors and anchor beam with different arrangement modes, were derived. Calculations of four layout plans of the yielding anchor rope box girder in the 1 000 m deep well of Zhaolou coal mine were analyzed. It is found that after the comparison of confining pressure values and distribution range, among the four programs, the confining pressure state formed in roof surrounding rock with a longitudinal-lateral program was the best, the longitudinal single anchor beam program following, and the last two were longitudinal double anchor beam program and cross anchor beam program. The preferential order of the layout plans corresponds to that of the support effect of different support programs in field test. The mechanism of different anchor beam arrangement modes is that the difference of confining pressure states in roof made by different programs was significant, and the confining pressure state, which had a positive correlation with support effect, was an important influencing factor for support effect of program.

Key words: confining pressure, three-dimensional mechanical model, arrangement modes of anchor beam, mechanism