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| Probe to the Fracture Mechanism Caused by Supercritical CO2 Explosion Under the Impact of Initial stress |
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Abstract 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.
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Received: 27 December 2016
Published: 28 October 2017
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2017, Vol. 38 
