Study on Mechanical Properties of Roof Rocks with Different Cutting Inclinations.

In the roof cutting pressure releasing gob-side entry retaining technology, roof cutting affects roof's mechanical properties greatly. In order to further improve the theory and method of roof cutting design, this paper puts forward a new design idea about roof cutting angle based on the mechanics theory analysis and model tests. Firstly, the surrounding rock stress state evolution process is summarized as four stages in this paper: supporting stress state, roof cutting stress state, pre-mining stress state and post-mining stress state. And what is pointed out is the stress state before mining can also affect the stability of the cutting roof. Then, gypsum specimens are taken as examples to do uniaxial compression tests and whose structural plane is constructed under the regular roof cutting angle [0°, 60°]. Tests get the c_θ and φ_θ of structural surface are 3.54 Mpa and 10.46° respectively. The results prove the single plane theory and are conductive to the cutting angle design under pre-mining stress state. Under the tests conditions, in order to ensure the roof entry retaining has high strength and elastic modulus, and can also take advantage of the function of the advanced stress concentration to make the roof slit more easily developed, the cutting angle is approximately designed as 23°. [ABSTRACT FROM AUTHOR]