超临界CO2气爆煤体致裂机理实验研究

为提高超临界CO₂气爆低渗透煤层增透技术的应用水平，进一步研究超临界CO₂气爆煤体致裂机理，利用自主研发的超临界CO₂气爆装置，在多通道电液伺服相似材料试验台上，对原煤和混凝土大试件(1 m×1 m×0.5 m)进行了超临界CO₂气爆实验，用动态应变仪采集试件内部监测点处的变形和破坏信息，并用工业窥镜对爆破孔内裂隙分布进行了观测。分析气爆应力波的变化规律和气爆后试件的破坏形貌特征可知，距离气爆孔由近及远依次分为粉碎区、裂隙区和震动区，其形成机理为:超临界CO₂冲击气爆孔周围介质并形成远超介质抗压强度的球面纵波，介质在径向压应力作用下发生粉碎性破坏，形成粉碎区；应力波传播能量逐步衰减，不足以使介质产生压缩破坏，然而脆性材料抗压不抗拉，其产生的环向应力仍然使介质产生径向裂隙，应力波之后具有准静态加载作用的高压CO₂气体进入裂隙形成气楔，促使裂隙进一步发育和扩展，形成裂隙区；裂隙区以外的介质在低能量应力波的作用下只发生震动，未发生明显破坏，即震动区。裂隙的扩展速度与其到气爆孔距离符合“S”形曲线衰减，裂隙的高速扩展发生在粉碎区，低速扩展发生在裂隙区；距离气爆孔越远，测点的峰值应变越小，相同距离内节理裂隙等结构面越复杂，峰值应变减小的幅度越大且应变波形差别越大。

Experimental study on fracture mechanism of coal caused by supercritical CO2 explosion

In this study we carried out a series of experiments on large specimens (1 m× 1 m×0.5 m)of coal and concrete using an explosive device and similar material test bench with multi-channel electro hydraulic servo to improve the application of the supercritical CO2 gas explosion in the low permeability coal seam and study the fracture mechanism of gas explosion.The internal deformation and failure information were recorded using a dynamic strain gauge,and fractures distribution in the blasting hole were observed using an industrial speculum.The gas explosion stress waves and the damage morphology after blasting show that damage areas from near to far are divided into a crushing zone,a cracking zone and a seismic zone.It is the corresponding formation mechanism that the supercritical CO2 impacts on the medium surrounding explosion hole,thereby forming the spherical wave,whose compressive strength is higher than that of the medium.Under the action of the radial compressive stress,the medium undergoes crushing destruction,and the crushing zone is thus formed.With the stress wave propagating,progressive attenuation of energy is not strong enough to cause the medium's compression failure.Brittle material is only good at resisting compression,but fails under tension.Circumferential stress generated by the stress waves still cause radial cracks.The high pressure CO2 gas with quasi-static loading action enters into fracture and forms a gas wedge that leads to the fracture's further development,called the forming of the cracking zone.Outside the cracking zone,the medium only vibrates under the low energy stress wave and no obvious damage occurs,and thus it is called the vibration area.The curve of the crack expansion velocity and distance from the gas explosion hole are in accordance with the "S" curve.High speed crack expansion occurs in the crushing zone,while the low velocity expansion occurs in the cracking zone.The farther away from the explosion hole,the smaller the peak strain of the measuring points,and the more complex the jointed fissure in the structure within the same distance;the greater the magnitude of the peak strain that decreases,the more different the strain waves.