Five models of cumulative blasting are established by using ANSYS/LS-DYNA to study the effect of decoupling coefficient on cumulative blasting to improve coal seam permeability. The formation and migration process of the shaped energy jets with two kinds of decoupling coefficient are compared and analyzed; also, the propagation of explosive stress waves is represented. The result showed that the air in the blast hole is the key to the formation and migration of the condensing jet. The air in the hole also could reduce the attenuation of stress wave in a certain range. However, if the decoupling coefficient is too large, the air in the hole will consume excessive explosive energy, which is also not conducive to energy transfer. Therefore, there is an optimum decoupling coefficient which can minimize the coal crushing area, increase the coal fissure area, and improve the gas extraction rate. Besides, the cumulative blasting tests were carried out in a coal seam. The test results show that decoupling charge could effectively improve coal seam permeability, and the blasting effect was better when the decoupling coefficient is between 1.67 and 2.
The dynamic effect of shaped charge blasting and its
application
in coal seam permeability enhancement have been investigated. Comparative
experiments of shaped charge blasting and conventional blasting to
fracture the concrete are carried out. Then, the propagation characteristics
of explosion stress waves under shaped charge blasting and conventional
blasting are analyzed by ANSYS/LS-DYNA. Finally, the fracture mechanical
model of shaped charge blasting is established. The experimental results
show that the width of the four main cracks formed after conventional
blasting is 0.3 cm, while the width of the cracks in the energy accumulation
direction after shaped charge blasting is 1.1 cm and the width of
that in the vertical energy accumulation direction is 0.4 cm. The
numerical simulation results show that the crushing area after shaped
charge blasting is “dumbbell type”, and the area is
smaller than that of conventional blasting. However, the cracking
area is “spindle type”, and the development of the fracture
degree is better than that of conventional blasting. In addition,
shaped charge blasting is used to improve the permeability of coal
seams. The results show that shaped charge blasting effectively improves
the permeability and gas extraction rate of coal seams.
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