Design On Hydraulic Dual Circulation Double-wall Drill Tools In Tunnel Explore

Complex formations, such as hard, brittle, tatter, leaky and sloughing formations, are frequently encountered in tunnel drilling of mines. When conventional wire core-drilling tools, dual tube drill pipe or simple tube drill pipe are used to drill these kinds of formations, disadvantages, such as low drilling efficiency, low core recovery, poor borehole quality, short bit life, many hole bottom accidents and high drilling cost, will appear. Borehole is generally designed as horizontal hole or inclined hole and the hole depth is less than200m in tunnel drilling. Serious water leakage in the boreholes happens frequently in tunnel drilling because of the mining blasting.According to the problems above, a set of small-bore hydraulic dual circulation double-wall drill tools suitable for tunnel explore, composed of dual-wall swivel, dual-wall drilling pipe(with dual-wall joint), dual-wall hole reamer and special diamond bit, were designed. This paper introduced the design idea and scheme, discussed the foundation of the parameter design and selection as well as the calculation on flushing fluid head resistance loss while drilling with the designed drilling tools. The application effect of the double-wall drill tools were verified by the field experiment.The main work and conclusion are as follows:(1) A kind of hydraulic dual circulation continous core drilling method was designed based on the comprehension and analysis of research status of reverse circulation core drilling tool at home and abroad, regarding to practical problems;(2) According to the hydraulic dual circulation continous core drilling method, a set of double-wall drill tools were designed, with the size of external tube φ45/38mm and the size of inner tube φ31/27mm;(3) Dual-wall swivel, dual-wall drilling pipe joint, dual-wall hole reamer and special diamond bit were designed to work with the dual-wall drilling pipe; (4) The flow pattern of flushing fluid in the drilling process was analysed and the water head loss was discussed;(5) The results of the field experiment show that, the core could be carried to hole-outside successfully, the flushing fluid returning to hole-outside accounts for about80%of total flushing fluid, and the set of double-wall drill tools could solve the problem of the flushing fluid leakage in tunnel explore.