Abstract:

Cutting-ground-breaking mechanism of compressed-air-jet is the technical and theoretical basis of the reverse circulation constant sampling and compressed air spurting drilling technology. The reverse circulation constant sampling and compressed air spurting drilling technology are efficient and environmentally protective drilling technologies of soft ground. So it is important to the research of cutting-ground-breaking mechanism of compressed-air-jet on the reverse circulation constant sampling and compressed air spurting drilling technology. First, the cutting ability of jet is 2.868×10³ kPa in the diameter of 8 mm by CFD software analysis. It is the same as the result of weighbridge method 2.468×10³ kPa, and it is larger than the breaking strength of soft ground. Secondly, the depth is 2.33 mm in 18 μs when using one jet by analysis of LS-DYNA. It applies the theoretical basis of the air spurting drilling. Finally, the pressure distribution of inside of soil body and the contour of air velocity is obtained by CFD software analysis. The results show that cutting-ground-breaking mechanism is divided into three steps artificially. First compressed-air expands sharply after entering into fissuring and microfissuring of soil body. Then the air continues expanding and outspreading during gaining confining pressure of drill. Finally soil body is broken and broken away from matrix as the result of reverse circulation suction force. It fits with the fault principle of soil micro-fissuring.

Key words: pneumatic-injection, ground-breaking mechanism, numerical analysis, experiment