初应力条件下超临界CO2气爆致裂规律研究

为研究地下爆破工程中初始地应力条件下超临界CO2气爆的致裂规律，利用自主研发的三轴加载式超临界CO2气爆实验系统，对不同应力组合工况下混凝土试件进行了超临界CO2气爆致裂实验，实验结果表明超临界CO2气爆爆破峰值压力低且高压持续时间长，致裂过程不同于传统炸药爆破，分为动态和准静态过程：应力波将气爆孔附近介质压碎形成粉碎区，在环向拉应力作用下粉碎区周围介质产生径向裂隙的动态过程，高压CO2气体进入裂隙形成气楔，促使裂隙继续扩展的准静态过程，得到了气爆后试件沿最大初始压应力方向开裂的规律。通过理论计算的方法分析了初应力作用下气爆过程中介质应力状态的变化规律，揭示了初应力影响裂纹起裂和扩展的机理：位于气爆孔最大初始压应力方向的介质产生初始环向压应力最小，在超临界CO2径向冲击产生的环向拉应力作用下首先发生开裂；位于气爆孔最小初始压应力方向介质中初始环向压应力最大，开裂所需的径向冲击压力增大，开裂滞后；垂直裂隙方向的应力抑制裂隙的张开而阻碍CO2气体的进入，同时增大了裂隙扩展所需的气楔压力，气楔作用效果大幅减弱，对裂隙扩展的阻碍作用显著。裂隙的扩展速度与扩展距离呈“S型”曲线关系，初始压应力越大，裂隙扩展相同距离降低的速度值越大，且压碎区和裂隙扩展范围逐渐减小。

Probe to the Fracture Mechanism Caused by Supercritical CO2 Explosion Under the Impact of Initial stress

The exploration is used in underground engineering and initial stress has an obvious effect on the exploration. The homemade traxial loading explosion system is used to investigate concrete fractures under the coupled action. Supercritical CO2 explosion experiments were carried out on specimens to explore the process of cracks extension with initial stress. The experiments indicate that: during the explosion, the peak pressure is low and high pressure duration is long, which is different from the traditional explosion. Stress of the medium and mechanism of cracks extension are studied in the process with initial stress. The process is divided into two parts, the dynamic and the quasi-static. Firstly, the medium near a blasting hole is crushed forming a crushing zone, and there is a radial crack outside the crushing zone due to circumferential tensile stress. Then high pressure CO2 diffuses into fracture forming gas wedge, so cracks continue to extend. It is found that cracks form in the direction of maximum initial stress. The initial circumferential compresssive stress of the medium in that direction is least and therefore, the specimen is cracked because of tensile stress caused by supercritical CO2 .The initial circumferential compresssive stress of the medium in the vertical direction is highest, so the stress should be large enough to cause cracks and the medium cracks relatively late. The stress in vertical fracture direction prevents gas from diffusion. Therefore, a higher pressure is needed to form wedge. The result is that the wedge affects and has a positive effect on hindering crack propagation. Crack expansion velocity is in accordance with "S" curve with distance from the hole. The greater initial stress is, the greater velocity decline is in the same propagation distance, and crushing zone and crack area gradually reduce. Above all, it is suggested that the distance between holes are broaden and holes are reduced to improve exploration efficiency in the exploration with initial stress.