A softening method of hard roof and coal seam controlled blasting

Abstract

Disclosed is a porous control method for blasting softening of a hard top plate and a coal seam. The method comprises the following steps that a drilling arrangement scheme is determined according to the hard top plate and the coal seam at an underhole place to be blasted, that is to say, three groups of blast-holes are formed along the overall length of a working surface in an up-down parallel mode at equal intervals, wherein the uppermost group of blast-holes and the lowermost group of blast-holes are both rows of control hole groups, the middle group of blast-holes is a row of blasting hole groups, and each control hole group comprises several control holes which are formed along the overall length of the working surface in a parallel mode at equal intervals. Thus, according to the method, the overall blasting softening effects on the hard top plate and a coal body are good; by conducting blasting softening treatment on the hard coal rock mass covering at the front of the working surface in advance, the limit caving step of the top plate at the rear portion of the working surface is reduced, and puking, nicking and other accidents are prevented from occurring on a mined surface; the method has the advantages of being high in drilling hole utilization rate, low in engineering workload, high in blasting safety factor and the like and can be applied to softening and caving control of various hard top plates and coal bodies under coal mines.

Description

technical field [0001] The invention relates to a blasting softening method for hard roof and coal seam porous control. Background technique [0002] In coal mining, the implementation of forced softening and caving measures on the hard coal rock roof is very important to ensure the safe and efficient production of the working face. As the mining face continues to move forward, part of the gangue directly on the top and part of the coal reserved for mining will continue to collapse, but it is difficult for the hard coal and rock mass to collapse automatically, thus gradually forming a mining face. Large and long cantilever coal and rock mass with coal body and support as the fulcrum. When these hard coal rock roofs are suspended to a certain step distance, it is impossible to control the instability of the hard coal rock roof simply by increasing the support strength of the working face. It is necessary to artificially force the roof to prevent roof caving and chipping on t...

AI Technical Summary

Problems solved by technology

However, the main disadvantage of this technology is that the blasting stress does not act uniformly on the coal and rock mass, and local stress concentration is prone to occur, resulting in more local crushed areas and fewer cracked areas, thereby reducing the effective utilization rate of blasting energy; The blasting and caving method of lagging working face is to construct blasting holes along the roof coal and rock mass in the rear direction of the working face. , resulting in more uncertain free surfaces, so the blasting minimum resistance line of partial blasting is smaller, making the roof blasting softening process full of uncertainty, and may even cause accidents

But on the one hand, limited by the heterogeneity of coal and rock mass and the uneven distribution of internal joints, beddings, and defects, the uncertainty of crack extension during fracturing is prominent, and local stress concentration areas are prone to appear. , leading to the failure and softening of the coal rock mass is not uniform enough

On the other hand, there are often well-developed fracture zones in the coal rock mass. These fracture zones either connect different fracturing pores or extend along the direction away from the coal rock roof. During the hydraulic fracturing process, Since the pressure water will preferentially flow along the direction of the largest pressure drop gradient, that is, along the well-developed fractures, this will lead to a serious loss of fracturing water pressure, failure to form a fracture network, and even lead to fracturing failure

Therefore, these uncertain factors to a large extent limit people's accurate judgment of the coming pressure and the step distance of the collapse, thus increasing the difficulty of people's safety control of the working face

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