The rotary drilling rig rapidly popularized in the construction project because of its efficiency, quickness, environmental protection, good hole-forming quality and other advantages. But in drilling hard rock, there are some problems, such as low service life of key position, low construction efficiency and others,. In this paper, these existing problems for power head, drill pipe etc. of working device of rotary drilling rig were analysed. The rotary drilling rig power head removable combined drive key design and rotating seal transition device design which is adapted to drill hard formation put forward the innovation. The rotary drilling rig power head and drill pipe were optimized design and improved. The productive test of rock pile hole drilling which drilling depth is 80m and hole diameter is 2m at fourth tender section on Qingzhi highway, GuiZhou province, shows that the working device optimized and improved well meet the requirements of the pile hole drilling construction under hard formation conditions. (C) 2014 Published by Elsevier Ltd. Open access under CC BY-NC-ND license.
