Experimental Study on CS-DSM Technology Applied in Soft Ground Treatment

In China， the insufficient capabilities of construction equipment and traditional methods have long limited deep soil mixing （DSM） technology， presenting a bottleneck for constructing large diameter and deep mixing columns with sufficient mixing uniformity and consistent strength in the thick soft soils. The newly developed CS-DSM technology represents a significant improvement in drilling tool structure design， monitoring and control systems， and construction processes to resolve the drawbacks of the traditional DSM， namely poor uniformity， low compressive strength， drilling bit balling， surface spoiling， and waste on binder materials. Full-scale field comparison tests were conducted between CS-DSM columns and DDM columns. By combining core drilling and static load tests， the differences between the two methods were studied in terms of pile integrity， continuity， cement-soil strength， and bearing and deformation characteristics of a single column. The results indicated that the CS-DSM method offered more controllable and reliable construction quality comparing to the DDM method， reducing construction time by 44.4%， increasing single pile bearing capacity by 25%， and improving initial deformation stiffness by 97.0%. Based on field experiments conducted on an intercity transit project in Guangzhou， this paper showcased major aspects of CS-DSM technology including equipment and column installation process， monitoring and controlling technique， characterization of column uniformity， and UCS test data of core samples. The results indicated that the "one mixing cycle with slurry injected during the down stage" process reduced construction time by 40% compared to the traditional method. The frame-type mixing tool achieved an excellent degree of mixing for columns with adiameter of 1 m and a length of 46 m， and ensured a blade rotation number T of 600/m above， equivalent to the soilcrete per unit volume experiencing more than 40 passes of the mixing blade. The cement contents in the weakly and strongly reinforced zones were 8% and 18%~20%， respectively. The 21-day core sample strengths from both zones were minimum 4 times greater than the design strength. In conclusion， the CS-DSM method stably enhances mixing uniformity and develop high strength along the full column length. The field trial studies on this new technology can provide a reference for the promotion and application of the CS-DSM method.