Abstract:

Small scale model test was conducted to investigate the technology factors related to contra-rotational shear deep soil mixing (CS-DSM) method, the effects of these factors, such as cement content, blade rotation number T, mixing energy E, rotation speed ratio of internal to external rod R_N on the uniformity and unconfined compression strength (UCS) of the mixing column were explored. The results show that the shearing motions of contra-rotational drilling tool can reduce excessive surface spoil and prevent entrained rotation phenomenon effectively, thereby greatly improve utilization of the binder material. The results of 18 model tests also reveal the inherent connection between T-E-UCS, and the internal relationship between machine operation parameters, mixing energy and strength of the columns. Construction parameters can be determined to ensure the target design strength by the provided calculation method. There is a peak value in the UCS-R_N curve, an optimal range of R_N = 1.8−2.2 is recommended for achieving peak strength of columns in engineering application. The presented technical basis has set the cornerstone for the construction process control and quality assurance as well as quality control of CS-DSM method.

Key words: technique of contra-rotational shear deep soil mixing, blade rotation number, mixing energy, rotation speed ratio of internal to external rod, CS-DSM method