Structural characteristics of key strata and strata behaviour of a fully mechanized longwall face with 7.0 m height chocks

Strata behaviour during the operation of super great mining height (SGMH) longwall face is different from that of normal mining height due to the extra large boundary of caved roof strata. The key to control the strata behaviour is to understand the structural characteristics of key strata (KS) and its movement law. Through field observation, physical model simulation and theoretical analysis on the first longwall face with 7.0 m mining height in the world, three kinds of structural model, which are affected by the relative position of KS in the overburden, are found and defined. Model A is defined as when the stable voussoir beam structure can be developed in the overlying KS and the strata behaviour is gentle. Model B is defined as when the cantilever structure is developed in the first KS while voussoir beam structure is developed in other overlying KS, and the continuous distance of periodic weighting (CDPW) is typically longer compared with that of normal mining height face. As to Model C, the structure of KS is the same as that in Model B, but the first KS will be forced to break in advance due to the break of the second adjacent overlying KS, which will present the weighting step and strata behaviour severity with a periodic alternating between long/gentle and short/strong. With respect to the three kinds of structural models, a method which is suitable for the calculation of working resistance for 7.0 m height chocks was proposed. The suitable working resistance for the 7.0 m height chocks of LW22303 face in Bulianta coal mine was determined to be 17,612 kN.

► The first key stratum usually behaves as cantilever structure in 7 m height chocks face.
► Three structural models of key strata have been built in 7 m height chocks face.
► A method for the working resistance calculation of 7 m height chocks has been proposed.
► The suitable working resistance for 7 m height chocks of LW22303 is 17,612 kN.