Ground improvement in southern Vietnam has been extensively studied and implemented in various port projects, with the deep mixing method (DMM) emerging as a relatively new technique applied in a few ongoing projects. In addition to enhancing slope stability, reducing settlement is also a primary objective of soft ground improvement. This research aims to evaluate the effectiveness of the DMM approach. Field mowing and data analysis were conducted to assess the method’s performance and verify the quality of DMM piles combined with surface treatment. A full-scale test was performed using a surcharge applied to the design load, enabling the verification of both elastic and long-term settlement. For comparison, a site utilizing the preloading method with prefabricated vertical drains (PVD) was also studied. The findings revealed that DMM piles significantly reduced vertical settlement and lateral movements by up to 95% compared to the PVD method. Additionally, the incorporation of surface treatment further decreased the stress concentration ratio due to an enhanced arching effect.