Study on deep borehole pre-fracturing blasting technology of thick and hard limestone roof

In order to solve a large suspended roof area problem occurred during the coal mining process in seam with thick and hard limestone roof, a theoretical . analysis, numerical simulation, site measurement and other means were comprehensively applied to study the deep borehole pre-fracturing blasting technology to contr ol the initial roof weighting step distance. The study showed that under the primary roof condition and according to the key stratum theory, first weighting interval of coal mining face was estimated to 59.2 m and the roof weighting was very serious.With the cracking expansion features of the deep borehole blasting analyzed with the num erical simulation, after the deep borehole pre-fracturing conducted in the open-off cut of the coal mining face, great secondary cracks occurred along the blasting boreh ole radially and the integrity of K2 limestone was destroyed.According to the strain responses features of the monitoring and measuring points around the blasting bore holes during the blasting process, the spacing between the boreholes determined was 6 m.The online monitoring and measuring system of the powered support working resistances showed that the average value of the first weighting interval was 34.3 m and the dynamic load coefficient was 1.35.The first weighting interval of the coal mi ning face was reduced by 24.9 m, the roof weighting intensity was weakened and a safety and high efficient production of the coal mining face was realized at the initial mining stage.