Whether the natural sand gravel stratum in the river bed would serve as the foundation of the superhigh faced rockfill dam or not was one of the key technical problems of the project.

Construction method of cast-in-place bored pile through sandy gravel stratum;

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.

The sand layer with gravel 12 m below the foundation level of 1 917.