Study On Broken Structure Characteristics And Stability Of Key Stratum Of Immediate Roof In Fully-Mechanized Face With Large Mining Height

The roof of large mining height fully-mechanized working face is likely to have key immediate roof due to large working height and overburden damage height. The research on effect of key immediate stratum on overlying strata movement law, displacement and stress distribution of working face, key immediate block stability, support resistance and pressure behavior is less now. Based on geological conditions of 15104 large mining height fully-mechanized working face of Shijiazhuang Mine with key stratum, this paper studies overlying strata movement law and surrounding rock controlling techniques systematically using theoretical analysis, numerical simulation and field test. The thesis obtained the following results:(1)Study structural characteristics of overburden of large height key immediate stratum. Overlying layers of working face are divided into four zones: irregular caving zone, regular caving zone, fractured zone and curve subsidence zone. Theory criterion of periodical breaking motion in the type of voussoir beam and cantilever beam are also provided.(2)Establish numerical models of large height key immediate stratum and study overlying strata movement law, stress and displacement distribution law and effect of horizon, blockness and hardness of key immediate stratum on advanced abutment pressure distribution law.(3)Establish initially broken mechanical model of key block of immediate roof, Theory criterion of initially broken slide instability and rotational instability is presented. According to temporary stable structure forming in the process of periodical broken rotation of immediate roof voussoir beam, two different calculated model of motion are established. Theory criterion of slide instability and rotational instability reaching broken blocks and without reaching broken blocks. It also analyzes influencing factors of complex breakage of key immediate stratum and main key stratum and the reasons for large and light periodical weight behavior.(4)Establish calculating models of slide instability and rotational instability for low cantilever beam of key layer of immediate roof and voussoir beam of mian roof. Computing formula of reasonable working resistance of slide instability and rotational instability for i MPact loading is presented and factors influencing support resistance is analyzed. Establish calculating models of voussoir beam of key layer of immediate roof and voussoir beam of mian roof and show computing formula of reasonable working resistance.(5)The initial weighting distance of 15104 face measured in Sijiazhuang Mine is 37 m and periodical weighting distance is 17 m and basically identical always without large or little periodical weighting distance, remaining distance is 4.1m on average, which verified the horizon of key stratum of 15104 working face is lied under immediate roof and break in the type of voussoir beam periodically.