空气反循环钻头井底流场分析及结构优化

Analysis on the Bottomhole Flow Field and Structural Optimization of Air Reverse Circulation Drill Bit

为改善空气潜孔锤反循环钻进技术在大口径嵌岩桩施工中的应用效果,运用Fluent软件对嵌岩桩施工用反循环钻头底喷孔水平倾角θd和扩压槽水平倾角θk做了进一步的分析和研究,得到θd和θk对反循环钻头抽吸系数ω的影响规律。在分析中发现原有反循环钻头中心贯通孔结构设计中的不足之处,并进行了优化,优化后的反循环钻头抽吸效果明显增强。采用优化后的结构加工了一个直径为660mm的反循环钻头,并进行现场钻进试验,试验效果良好,平均钻进效率为6.00m/h,成功嵌入微风化岩层表面,能够满足嵌岩桩施工对嵌入微风化岩层和孔壁稳定、无塌孔的要求。

In order to improve the application effect of the reverse circulation air hammer drilling technique, on the construction of rock-socketed pile by using software Fluent, the authors analyzed the horizontal inclination angle θd of flushing nozzles and horizontal inclination angle θk of pressure-restoring grooves on the reverse circulation drill bit used in the construction of rock-socketed pile. The effects of the θd of flushing nozzles and the θk of pressure-restoring grooves on the suction coefficient co of reverse circulation drill bit are obtained. Meanwhile, aiming at the deficiency in the structure design of central hollow-through hole on the reverse eirculation drill bit, we optimized the structure of reverse circulation drill bit; and thereby, the suction capacity is obviously enhanced. A 660 mm reverse circulation drill bit adopted to the optimized structure is processed, and the field tests are carried out. It can be concluded from the test results that the effect of reverse circulation formation is good, the average penetration rate is 6. 00 m/h, the surface of weakly weathered rocks is successfully drilled out. This meets the requirements on drilling out the surface of weakly weathered rocks and stability of borehole wall without borehole collapse.