Concentric drilling systems by DTH hammer which designed to drill and case a hole simultaneously through unstable ground conditions.The driver bit incorporated with a one-time used ring or reusable ring makes a full face head design which significantly improves the penetration rate and hole straightness of drilling.The internal flushing grooves together with the built-in casing shoes gives a good seal to the button of the drilling hole, and thus mini missing the disruption of the surrounding of the drill hole.It is suitable for drilling water wells, geothermal wells, short micro piles,medium mini-type grouting hole of building,dam and harbor project.
