Based upon cavity effect of explosive, researching and manufacturing a tool breaking erratic in well and combining with wallscraper drilling resolved large diameter well completion technology in erratic stratum and improved drilling efficiency from several times to dozens times and quickened the speed of well completion.

By the analysis of present drilling ways,and according to the characteristics of gravel strata,application feasibility is put forward for DTH hammer concentric simultaneous casing drilling tool in gravel strata,and analysis are made on the structure principle and characteristic of drilling tool.

Through applying downhole hammer concentric simultaneous casing drilling method,the difficulties that drill in gravel strata are solved out fundamentally,the authors consider downhole hammer concentric simultaneous casing drilling is an effective way for gravel beds in combination with a case of rock-soil engineering survey in Duyun Cit

Abatract The paper firstly introduces the designing principle of a new-type alloy-diamond bit for the gravel stratum, secondlyexplains briefly the mechanism of matrix composition for the new-type bit.

Drilling in gravel stratum is one of present difficulties in drilling area with low drilling speed,short service life of bit and high drilling cost.

When large dismeter water well is constructed in cobble and boulder strata drilling by percussion machine is not proper to be used as limited by condition.