Study on the interaction mechanism between the contra-rotational shear deep soil mixing drilling tool and the soil

Deep soil mixing piles are established for soft soil stabilization, yet the internal mechanism by which drilling tools achieve complete soil-cement homogenization remains unclear, hindering precise quality control in column formation. In this paper, a new type of contra-rotational shear deep soil mixing (CS-DSM) drilling tool was proposed and the detailed design information was thoroughly introduced. The discrete element modeling method was applied to establish a coupling model of CS-DSM drilling tool and soil verified by a laboratory model experiment. Soil particle moving path analysis quantified mixing dynamics during drilling-down and drilling-up phases. The results explained the internal mechanism that the soil particles could be fully sheared, stirred, and mixed in the horizontal and vertical directions to form a uniform soil cement column. The average VC of particle X1-X3 was 1.9 times larger than that of particles Y1-Y3, which indicated that soil particles along the x -axis and y -axis exhibited distinct moving patterns. The mixing efficiency during drilling-down and drilling-up was quite different, and the VC during the drilling-down process could be 146.7 times larger than that during the drilling-up process. In practice, reducing drilling speed or increasing rotational velocity during drilling-down enhances CS-DSM pile quality under identical conditions.