| Gravel layer is a usual complex instable formation in drilling engineering. There are some basic features such as looseness of structure, increment, unequal sized grain. It is commonly to form discrete single-grained structure. Grains which are under water or in the air suffer gravitational selection to stack and form this structure. The junctions between grains are just though point and point. It is hardly any link or awfully weak link between grains. Furthermore, the interstice is relatively big, and the position of grains is not fixation. Under the function of big pressure and dynamic load, the grains may be moved which may cause the soil body distortion.At present, the relatively ripe methods of drill in gravel layer are mostly double-wall drill pipe reverse circulation drilling, auger stem breast wall drilling and down-the-hole hammer follow down drilling. There are mostly two standards of down-the-hole hammer concentricity follow down drilling which above the recital investigation in air drilling. One is the least gas kinetic energy. The other is the terminal velocity of detritus sedimentation.The author takes consider of the aerial condensability. According to Newton's second law and gas equation, it is elicited to the gas pressure distributives in the drill pipe. The slippage model help to elicit the pressure distribution of stream-stereo two... |
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