The theoretical equation of initial top-coal boundary (ITCB) is one of the fundamental problems of top-coal drawing law in longwall top-coal caving (LTCC) mining. The granular mechanical model of ITCB is established based on loose medium flow field theory. By analysing the stressed top-coal on ITCB along the section of coal seam thickness and face advancement directions, the theoretical equation of ITCB is deduced respectively in the two conditions of first gangue drawing out and excessive gangue drawing out. The theoretical equation is further modified by a correction coefficient k, which is given by a large number of experimental data. Meanwhile, it is found that the ITCB at excessive gangue drawing out condition is in the special shape that "the top opening is elliptical and the bottom opening is rectangle". The theoretical equation of ITCB can provide meaningful guidance to the improvement of top-coal recovery ratio in LTCC.
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Wei et al. (2018) studied this question.
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