煤体高压空气爆破模拟试验研究

A simulation experimental study on high-pressure air blasting of coal

高压空气爆破(high-pressure air blasting,HPAB)是通过瞬间释放高压气体冲击煤体达到增加煤体渗透性的一种物理爆破技术,该研究通过自主研发的高压空气爆破试验系统开展模拟煤体高压空气爆破试验,试验过程中对试块的超声波波速、应变和裂纹扩展速度进行测试,基于试验结果和损伤断裂力学理论揭示了煤体高压空气爆破应力波传播与衰减规律和损伤断裂过程与机理。煤体中高压空气爆破应力波和炸药爆炸应力波的波形特征相同,但高压空气爆破应力波峰值小、作用时间长、脉宽长、衰减慢(α=2-μ/(1-μ))。煤体首先在高压空气爆破应力波作用下产生初始径向裂纹,初始径向裂纹以0.15~0.40倍应力波波速扩展。随后,高压气体、瓦斯气体和远场应力共同作用驱动初始裂纹以0.12~0.14倍应力波波速度稳态扩展,最后远区煤体内部的一系列周期性原生裂纹在弹性应力波、原岩应力和瓦斯气体的共同作用下在小范围内缓慢扩展。

High-pressure air blasting(HPAB)is one type of physical blasting techniques to increase the permeability of the coal seam by instantly releasing high-pressure air to impact the coal.In this paper,a experimental study on the HPAB of simulation coal was conducted using a self-developed HPAB experimental system.To reveal the propagation and attenuation law of stress wave,and the process and mechanism of coal damage-fracture under the action of HPAB,the ultrasonic velocity,strain and cracks propagation speed were tested.Based on the experimental results and the theory of damage fracture mechanics,it can be concluded that the stress waveform generated under the action of HPAB is the same as that generated under the action of explosive blasting.However,the peak stress of the HPAB stress wave is smaller than that of the explosive stress wave.Moreover,the action time and the pulse width of the HPAB stress wave are longer than that of the explosive stress wave,and the HPAB stress wave decays at a slower speed(α=2-μ/(1-μ)).Under the tensile action of the HPAB stress wave,the initial radial cracks in coal are generated firstly,and the initial radial cracks propagate rapidly at 0.15-0.40 times the speed of the ultrasonic velocity.Subsequently,the initial radial cracks propagate steadily at 0.12-0.14 times the speed of the ultrasonic velocity with the combined effect of high-pressure air,the methane gas pressure,and the in-situ stress.Finally,the periodic original cracks,which are in the far area of the blasthole,slowly propagate in a small area with the combined effect of elastic stress wave,the methane gas pressure,the in-situ stress and the interaction between parallel original cracks.