Abstract: With the development of engineering technology and the extensive distribution of new constructions, new buildings have to be constructed on soft soil where various ground improvement methos are developed. This paper presents a case history of ground improvement using vacuum preloading method. The improvement effect was measured by the vane shear test and laboratory tests before and after the ground improvement. The following results are obtained: the soft soil before the treatment has poor mechanical properties, poor stability, low strength, fluid plasticity, high compressibility, and large thickness, and is not suitable for a bearing layer; After the ground improvement, the undrained shear strength value of soil increased by 262.5% compared with that before the treatment; and the remolded undrained shear strength value increased by 225.3%. After the ground improvement, various mechanical performance indexes of the soil mass are improved, and the soil is significantly improved, the treated soil is suitable for the building foundation construction.

Key words: Vane Shear Test, Evaluation System, Ground Improvement, Laboratory Tests