压缩气体射流切割破土机理

Cutting-Ground-Breaking Mechanism of Compressed-Air-Jet

压缩气体射流切割破土机理既是气力喷射反循环钻孔技术的基础也是其重要的理论依据,而气力喷射反循环钻孔技术又是一项高效环保的软地层钻进技术,所以压缩气体射流切割破土机理研究对于气力喷射反循环钻孔技术有重要意义。首先,应用CFD软件模拟,得出8mm直径喷孔切割能力为2.868×103 kPa,与单喷孔地秤实验得到的2.468×103 kPa拟合较好,其值都远远大于软地层破坏强度;其次,通过LS-DYNA模拟可知单次喷射18μs时的切割深度约为2.23mm;最后,用CFD软件分析得到土体微裂隙断裂压力分布图及气体流速图。结果表明,压缩气体射流切割破土机理为:压缩气体沿薄弱环节进入孔隙和微裂隙后急剧膨胀,在恢复到钻孔围压过程中继续膨胀、扩张,同时在反循环抽吸力的共同作用下使土体结构破坏、断裂脱离母体;符合土体微裂隙断裂原理。

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.