Abstract: According to the purpose and characteristic of the weakening blast of hard top-coal in fully mechanized caving faces, that the dynamic breaking process of hard coal mass on blasting load is also a process to accumulate continuously damage is pointed out; and by the blasting dynamic deformation ratio experiment of the big coal samples, the power function of the deformation ratio attenuation corresponding to the blasting deformation wave peak of the hard top-coal weakening blast is proposed; and based on that with the rock blasting damage models of Tarlor and Drady etc., the distribution function of the macro-damage breakage degree of the top-coal weakening blast is derived; and the parameters and coefficients correlating the calculation are presented. It is the base to analyze and determine the rational parameters of the top-coal weakening blast.

Key words: hard top-coal, weakening blast, macro-damage breakage degree, attenuation law of deformation ratio