A model for top coal recovery ratio assessment and its application in longwall top coal caving

Top coal recovery ratio is one of the core issues in longwall top coal caving ( LTCC) mining. In order to clarify the criterion for stopping the caving and maximizing the top coal ratio,the equations of the top coal boundary and drawing body were derived based on the stochastic medium theory,and using the drawing body equation,the evo- lution characteristics of drawing body was analyzed. Considering the top coal boundary and drawing body,the theoreti- cal model for calculating the top coal recovery ratio and rock-mixed ratio was established,which was used to model the interrelationship between the top coal recovery ratio and rock-mixed ratio under different top coal thicknesses. Then,combined with the production practice in Tashan mine in China,two model experiments with different top coal thick- nesses were carried out to obtain the relation curve on the top coal recovery ratio and rock-mixed ratio. Finally,aimed at the working faces 8101,8102 and 8111 in Tashan Mine,the field observation on the top coal recovery ratio and rock-mixed ratio was conducted,and the relation curve on the top coal recovery ratio and rock-mixed ratio was ob- tained based on the measured data. To prove the theoretical analysis,the relation curves from the model experiment and field observation were analyzed and compared to the theoretical curve,respectively. The results show that during the top coal drawing process,the deflection angle of drawing body decreases with the increase of drawing body height, i. e. the top coal drawing body gradually inclines toward the coal wall,and the shape of drawing body gradually turns into a cut variant ellipsoid from an unrepresentative round. For the fixed cutting height and drawing body height,the deflection angle and the drawing volume are bigger when the thickness of top coal seam is small than that when the thickness of top coal seam is large. top coal recovery ratio increases nonlinearly with the increasd of rock-mixed ratio. The concepts of top coal inflexion recovery ratio and inflexion rock-mixed ratio were presented,and the rock-mixed ra- tio 9% -16% can be used as the criterion for stopping caving in practical LTCC mining.