Abstract: In order to study the characteristics of overburden movement, breaking and evolution of rock pressure in fully mechanized caving face, according to the 302 working face in Cuimu coal mine, the similar material model experiment is performed. The breakage characteristics and rock pressure evolution of roof are observed during the coal mining. Based on the test results, a mechanical analytical model of the fracture at the coal wall is established, and the formula for calculating the critical support strength is deduced. The effects of the tensile strength, load and the thickness of the basic roof on the critical support strength are investigated. The mechanical criterion of the breakage at coal wall in fully mechanized caving face is formed, and the supporting effect of hydraulic support in the 302 fully mechanized caving face in Cuimu coal mine is analyzed. The result shows that the cantilever length of basic roof gradually increases during the advancing process of fully mechanized caving face. Together with rear fractured roof, the structure of "cantilever and articulated rock beam" is formed. The hydraulic support is under the protection of the structure, making a small working resistance. If the basic roof fractures and becomes unstable at the coal wall, the support resistance rises rapidly with the safety valve opening. Even the support crushing accidents easily occur. With the increase of the load on the basic roof, the critical support strength of tensile fracture linearly increases. However the tensile strength of the basic roof has little influence on the critical support strength of tensile fracture. The study in this paper provides a method for the prediction of the breakage at coal wall of basic roof and the support crushing in the fully mechanized caving face.

Key words: fully mechanized caving face, similar material model experiment, overburden breakage, support crushing, the critical support strength of tensile fracture