Abstract：Research purposes：In the course of the geological survey for Tianjin-Qinhuangdao Passenger Dedicated Line, the core-drilling ratio was very low in unconsolidated and fracture strata or in soft inter layer, even the rock core was burnt, polluted and its structure was damaged when using conventional drilling techniques because the rock core suffered the wash of the fluid, vibration of the drilling bit and the friction of the inner tube. It could not meet the railway prospecting criterion, so the drilling technique must be improved.
Research conclusions：(1) The applicable test of drilling showed the Single-acting Double-tube diamond bit could prevent the wash of the fluid, reduce the vibration of the drilling bit and remain the original core structure, therefore to avoid the pollution and burnt damage to the rock core. (2) Application of the Single-acting Double-tube diamond bit could enhance the core-drilling ratio to 91% maximally and the core-drilling ratio could meet the the railway prospecting criterion. (3) There were some problems in using the Single-acting Double-tube diamond bit, so the method of using Single-acting Double-tube diamond bit still could be improved in further tests and applications.
2010, Vol. 27 
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