Study On Blasting Effect Of Bottom Air-Decked Charge Structure

Air-decked charge structure can prolong the action time of stress wave and significantly reduce or not produce blasting crushing zone through the axial uncoupling relationship between.charge package and hole wall,effectively improve the utilization rate of explosive energy and blasting crushing quality,and is widely used in engineering blasting practice.However,relevant researches at home and abroad are still in the experimental and semi-empirical stage,and neither a systematic theoretical system nor a relatively perfect practical experience has been formed.In this paper,for explore the mechanism of bottom air-decked charge structure,seek for a better proportion of air deck,and compare the blasting effect of bottom air-decked and water-decked charge structure,theoretical analysis,numerical simulation and field test were used to study the bottom air-decked and water-decked charge structures.The main research achievements are as follows:(1)Based on the shock tube theory and the reflection and transmission theory of stress wave,the stress wave propagation process in the blasthole was analyzed.The stress waves in blasthole were mainly composed of three stress waves,and the stress waves were reflected and transmitted by these three stress waves at five medium interfaces.In addition,the hole-bottom rock mass was subjected to multiple reflected stress waves and the bottom air-decked charge structure has the effect of enhancing fragmentation at the bottom of hole.(2)ANSYS/LS-DYNA numerical simulation software was used to simulate and analyze the bottom air-decked charge structure with different air-decked ratios.The theoretical analysis of the stress wave propagation process at the bottom of hole spacer and the reinforcing effect of the bottom air-decked charge structure were verified,and the better air-deck ratio was 20%～30%.(3)The blasting test of in-situ rock core was carried out by using the method of simulating blasthole with steel tube in Jinchanghe mine,Baoshan.Through the experimental study of the bottom air-decked charge and bottom water-decked charge structure with different spacing ratios,the enhanced fragmentation effect of bottom air-decked charging structure on rock mass within the range of the bottom of hole is further verified.In addition,according to the analysis of the blasting phenomenon of the test device and core damage value,the optimal air-decked ratio of the bottom air-decked charge was 20%-30%,which is consistent with previous research results and numerical simulation results.(4)The bottom air-decked charge structure and bottom water-decked charge structure with different spacing ratios were numerically simulated.Compared with bottom water-decked charge structure,the bottom air-decked charge structure was obviously reloaded,and the stress wave action time was longer,and the maximum subsequent pressure was higher than the initial pressure,indicating that bottom air-decked charge structure has a strong reflected stress wave effect.