Experimental Application on Reverse Circulation Drilling Technology with DTH Air Hammer in an Open Pit Mine in Sichuan

The technology of reverse circulation drilling with DTH air hammer which has shown lots of peculiarities such as high drilling efficiency, good quality of borehole and unique adaptability of complex formation has been widely used in developed countries. In the paper, we have carried out analysis and research on the flow field model inside the holes of reverse circulation bit without bottom injection hole and double hole reverse circulation bit. The research shows: reverse circulation bit without bottom injection hole is 21% higher than reverse circulation bit with bottom injection hole in respect of flow speed injected from the interior injection hole. In the central channel beneath the interior injection hole, the upward flow speed of reverse circulation bit without bottom injection hole is higher than that of double hole reverse circulation bit, and its speed remains constant. So it shows than reverse circulation bit without bottom injection hole has an advantage over double hole reverse circulation bit. In order to test effect of reverse circulation with different drilling assembly, the technology of reverse circulation drilling with DTH air hammer is adopted to carry on a series of field tests in an open pit mine in Sichuan. Finally, the conclusion of this paper from onsite test is: the average drilling speed of drilling machines with reverse circulation bit without bottom injection hole is 8.83 m/h, and has very good reverse circulation results.