A Study of Fractal Deep-Hole Blasting and Its Induced Stress Behavior of Hard Roof Strata in Bayangaole Coal Mine, China

Abstract

The phenomena of strong pressure occurrences have been observed many times in the #311103 working face of the Bayangaole Coal Mine. Deep-hole blasting measures were used to relieve the pressure in order to decrease the danger levels of these strong pressure occurrences on the working face. The blasting layouts proposed in this study differed from the conventional blasting layouts of a “straight-line” design by instead utilizing “triangular-fractal” and “deep-shallow-fractal” for the purpose of successfully driving the explosive efficiency and enlarging the roof-blasting range. The fractal dimension of the “triangular-fractal” blastinglayoutwascalculatedas1.1274.Thefractaldimensionofthe“deep-shallow-fractal”wascalculatedtobe1.556.Thefractal dimensionsofbothimprovedlayoutswerefoundtobelargerthanthatofthe“straight-line”blastinglayout(1.0).Inaddition,the Misesstressevolutionandthechangedtrendoftheeffectivestressandstrainoftheobservationpointsaroundtheholeofthethree layouts are analyzed and compared by LS-DYNA numerical simulation software. The results indicated that the “deep-shallowfractal” blasting layout had the most effective blasting effects, followed by the “triangular-fractal” blasting layout. It was determinedthatthetraditional“straight-linear”blastinglayouthadtheleasteffectiveblastingeffectsofthethreeexaminedlayouts. In summary, the implementations of the improved fractal blasting layouts in this study were found to be conducive to the enhancement of the blasting effects