For rotary drilling in ground investigation works, drilling fluid is normally used to clear and clean the cuttings from the drilling bits and transport them to the ground surface. Moreover, it also serves to produce a cooling effect to the drilling bit. In addition, the stability of boreholes can be enhanced and the drilling fluid also produces lubricating effect to the bits.
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Compressed air when used as a drilling fluid possesses several advantages. Firstly, the use of compressed air can reduce the loss of fluid during circulation which is commonly encountered for water being used as drilling fluid. Secondly, the efficiency of air to clean drilling bits is higher than other types of drilling fluids. Thirdly, the moisture condition of in-situ soils would not be affected by air when compared with water as drilling fluid.
In addition, in cold countries the occurrence of freezing of drilling water/mud can be avoided by using air. However, special attention should be taken to avoid breathing the generated dust when compressed air is employed as drilling fluid and dust suppression measures have to be properly implemented.
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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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