Abstract: Abstract: As the constrained boundary of drawing process after initial top coal drawing, the development process and morphological characteristic of initial interface between coal and rock is vital to subsequent drawing process under longwall top coal caving technique. Based on granular mechanics, mechanical model of initial interface between coal and rock was built combined with the result of 3-D loose top coal drawing experiment and PFC3D numerical simulation. The result after deep analysis shows that the basic reason for the specific morphology of initial interface between coal and rock (the slope of initial interface between coal and rock decreases with the increment of height ) is that different positions on the initial interface between coal and rock undertake different lateral pressure. The drawing interval and the height of broken immediate roof are the important factors to control the morphology of initial interface between coal and rock. This paper expounds the relation between the drawing interval and the size of initial funnel of drawing coal. The paper also proposesd the method to determine proper height of broken immediate roof in order to make the morphology of initial interface between coal and rock be favorable to subsequent drawing process.

Key words: Key words: initial interface between coal and rock, drawing interval, longwall top coal caving, funnel of drawing coal, height of broken immediate roof