Experimental Study On Damage Characteristics Of Shaped Charge Blasting In Thin Coal Seam Containing Dirt Band

As an important part of coal reserves in China,thin coal seam resource reserves are constrained by geological conditions,mechanized level of mining equipment,mining technology and mining cost,and the output of thin coal seam has been poor.Then,in the mining of thin seam containing dirt band,especially hard dirt band,the restriction is greatly improved,which makes mechanized comprehensive mining difficult to achieve smooth results.At present,advanced deep-hole pre-splitting blasting is one of the effective methods to weaken the hard dirt band in thin coal seam,and the purpose is to pre-splitting the hard dirt band in coal seam in advance in front of the working face.However,under the blasting of ordinary charge structure,the cracks generated by blasting spread disorderly around the blasting hole,which leads to a large number of cracks in the coal body,so that the blasting energy cannot be used to the maximum extent to weaken the dirt band.Therefore,it is necessary to carry out the research on weakening the dirt band in thin coal seam by using the technology of shaped charge blasting,and to conduct in-depth research on the damage and crack evolution characteristics of the dirt band under the action of shaped charge blasting,so as to provide theoretical and experimental basis for pre-weakening the dirt band in thin coal seam by shaped charge blasting and ensure the safety and efficient mining of thin coal seam with dirt band.In this paper,the mechanism of crack caused by dirt band in shaped charge blasting is analyzed.According to the blasting mechanics and the rock fracture mechanics,based on the two types of location of blasting holes in the thin seam with dirt band,two kinds of fracture mechanics models of blasting holes with two-way energy accumulation and the direction of energy accumulation parallel to the direction of dirt band and the one-way energy accumulation and the direction of energy accumulation perpendicular to the direction of dirt band are established respectively The relationship between stress wave intensity of ordinary blasting and shaped charge blasting in the direction of energy accumulation in the two models are obtained,and the calculation formula of the range of fracture area and crack development area formed in the dirt band are derived.Based on the similarity theory analysis,the similar proportion coefficient and the composition and proportion of similar materials are determined by the similar proportion test.The static and dynamic mechanical properties of similar materials are tested by RMT-150B rock mechanics experiment system and Hopkinson compression bar system.Through the analysis of explosion similarity,the conditions that need to be satisfied for the similarity between the simulated test specimen and the actual explosion in the field are determined.The similar simulation test platform for damage characteristics of dirt band in shaped charge blasting with internal space of 1200 mm×900 mm×1000 mm is designed and constructed.Four groups of similar simulation and contrast tests are designed for the damage of dirt band in ordinary blasting and shaped charge blasting when the blasting holes located in different positions.The propagation law of stress wave,the damage of dirt band and the evolution characteristics of cracks in the blasting process are studied by means of dynamic strain gauge,network parallel electrical method,high-speed photography and other testing means.It is revealed that when the blasting holes are located in different positions,the law of damage and crack evolution of dirt band under the action of ordinary blasting and shaped charge blasting.By using ANSYS/LS-DYNA numerical simulation software,the formation,migration,penetration into rock mass and the expansion,and development of cracks in rock mass are simulated,and the original rock area simulated by the four models in the similar simulation test is simulated.Further,the damage and the law of fracture evolution of dirt band under the action of ordinary blasting and shaped charge blasting when the blasting holes located in different positions are studied.In this paper,through theoretical analysis,similar simulation test and numerical simulation,the damage and crack evolution characteristics of dirt band under the action of ordinary blasting and shaped charge blasting when the blasting holes located in different positions are studied in depth.The results show that when the blasting holes are located in coal seam,due to the penetration effect of concentrated energy jet,the peak value of compressive strain in the dynamic loading stage is 1.18 times than that of ordinary blasting in the direction of energy accumulation.With the influx of detonation gas,the peak value of compressive strain in static loading stage is 2.99 times larger than that of ordinary blasting,and the duration time is 1.79 times longer.The average abnormal coefficient of electrical resistivity caused by shaped charge blasting in the section of dirt band is 1.07 times of that of ordinary blasting.The vertical cutting damage of dirt band is increased and the damage to coal is reduced by shaped charge blasting.When the blasting holes are located in dirt band,the peak value of compressive strain in the dynamic loading stage is 1.16 times than that of ordinary blasting in the direction of energy accumulation;the peak value of the compressive strain in the static loading stage is 2.93 times larger than that of ordinary blasting,and the duration time is 1.96 times longer.The average abnormal coefficient of electrical resistivity caused by shaped charge blasting in the section of dirt band is 1.21 times of that of ordinary blasting.Shaped charge blasting can form two-sided guiding cracks in the direction of energy accumulation,so that the blasting energy can act on the dirt band to the maximum extent,which is conducive to the transverse cutting and generation of through cracks.Thus,the damage and crack evolution characteristics of dirt band under the action of ordinary blasting and shaped charge blasting when the blasting holes are located in different positions are revealed.The research results have important industrial value and social significance for the thin coal seam with dirt band to weaken the dirt band,increase the damage degree of the dirt band,inhibit the waste of coal resources,and then realize the fully mechanized,efficient production and output increasement of the thin coal seam with dirt band.Figures[94]Tables[17]References[161]...