Calculation method and classification standard of rock stratum strength index based on petrophysical and mechanical parameters

The classification of surrounding rock stability is the key basis for supporting design in underground coal mines,and the physical and mechanical parameters of rock are important indicators of the classification and classification of surrounding rock strength.Therefore,on the basis of studying the physical and mechanical properties of the coal measure strata in Shendong Mining Area,this paper studies the relationship between the physical and mechanical parameters of the rock and the strength of the rock formation by means of theoretical analysis and field measurement.The calculation formula of the strength index of the rock layer (rock mass) of the mechanical parameters and the classification method of the lithological sequence,the stability of the rock layer is divided into five categories which very soft rock layer,soft rock layer,medium hard rock layer,hard rock layer,and extremely hard rock layer according to the rock stratum strength index.The relationship between the strength of the rock formation and the mechanical properties of the rock is revealed,the connection between the physical and mechanical properties of the rock and the rock formation (rock mass) is established.The strength index of the overlying strata of the coal is classified and the strength index is classified,and it is concluded that the 5-2 coal direct roof strata belonged to the Ⅱ hard rock strata,and the basic top belonged to the Ⅰ extremely hard rock stratum.The relationship between the strength index of the overlying strata of 5-2 coal,the appearance of rock pressure and the movement of strata is discussed.The internal causes of the large first-time pressure step and the fast subsurface velocity of the Daliuta Coal Mine are revealed.