Abstract:Based on the mechanical model of fixed beam with gravity in account,the rupture reqularity of hard and massive roof of longwall face is analyzed. In this paper,the structure of the main roof before its initial rupture is considered as the fixed beam,and the gravity of hard roof is considered as the centralizing force. By using elastic theory and analyzing the stress field of fixed beam under gravity,the mechanics judgement model of the overlying strata in three kinds of possible movement is suggested,which are that (1) the shearing with and without the weak interbedding to directly cause the key falling of strata,(2) rupture resulting from pressure and shearing in the whole strata,and (3) rupture of the strata close to two ends of beam. The suggested mechanics judgement model has been tested by field experiments,and it is useful for the prediction of the initial rupture and span of the main roof of the hard and massive strata.