| Soft rock, widely distributed on the surface of the earth, possesses distinct deformable characters under specific environment, and often bring about special problems in physical design and construction technique. Compared with drilling in soft rock of higher strength and poorer brittleness, the drilling of concrete pile by drag bits in soft rock sees higher efficiency. Therefore, it is essential to study and summarize a well-developed set of construction tool configuration and technique parameter in the aim of promoting drilling efficiency and reducing construction cost.On the basis of consulting a great number of related documents home and abroad, this thesis has thoroughly and systematically genera-lized the broken rock mechanism of the drag bits, the design of drag bits, and drilling technology of the drilling concrete pile. On adopting the combination of theoretical analysis, physical model test and engineer application, along with the simulation theory and the simulation technique of material with similar lithology lith, the thesis has figured out the mixture of three kind of soft rock—mudstone, siltstone and fine sandstone. Besides, the soft rock test piece used for drilling simulation experiment has been made, whose conclusion indicates that the assemble angle of drag bits and the parameter of drilling method have a considerable influence on pore-forming efficiency. On using the Logistic model and BoxLucas1 model, the nonlinear fitting is carried on to the relation of drilling speed and drilling pressure, drilling speed and retating speed, the results of which have very good guidance to field experiment. The thesis has put forward the technology parameter for improvement of drag bits. the research findings have been applied to entitative construction and achieved good applicable effect. Meanwhile, the findings also provide experience for engineering practices and related research.
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