Abstract: To avoid support crushing and water inrush disaster in the working face of improving upper limit in Huainan mining area, based on the comprehensive strength of strata in caving zone and whether or not existing hard stratum in fractured zone, the structure of overlying strata were divided into four types, namely, I, II, III and IV. In addition, the mechanics models of different strata structures were established, the critical support resistance was deduced, the instability criterion of support crushing was determined in the working face of improving upper limit, and the factors influencing critical support resistance of support crushing were further analyzed. The results show that the measures such as reducing length of working face, lowering mining height, keeping the integrity of immediate roof, preventing roof in the gob form suspending, strengthening the rib of working face, and drainage for decreasing water pressure before mining, etc. would be in favor of the stability of support in the working face of improving upper limit.

Key words: the working face of improving upper limit, comprehensive strength of roof strata, classification of overlying strata structure, critical support resistance of support crushing, instability criterion of support crushing