NUMERICAL SIMULATION ON MECHANICAL CHARACTERISTICS OF DEEP-HOLE PRESPLITTING BLASTING IN SOFT COAL BED

The technique of deep-hole presplitting blasting in coal bed is widely used for gas predrainage recently; but its blasting theory is not clear up to now. Based on the parameters of blasting,explosive and coal bed achieved from the mines,the mechanism of the presplitting blasting in coal body is studied by three-dimensional numerical simulation method. A numerical computational model in coal bed is constructed for cylindrical charge. The damage ranges of elements and zone influenced for the gas drainage by stress waves are investigated in coal body. The results show that the maximum radius of the area crushed by blasting is up to 40 cm,while radius of rate of gas drainage changed by blasting load is less than 10 m. It is also demonstrated that the improvement of draining effect is most obvious within 4 m around the hole. The stress propagation feature is discussed in draining holes with different distances. The differences of stress distribution,which is caused by the different detonation velocities for the primacord and emulsion explosive,are studied for the first time for clarifying some misunderstandings. The displacement field variations of the holes with different distances are analyzed in soft coal strata. Computation results are in good agreement with the gas draining data measured from the mine before and after blastings. This investigation is beneficial for promoting development of the presplitting blasting technique for gas control.