Abstract: To quickly obtain the strength and deformation parameters of the soft soils before and after the ground improvement, and to evaluate the improvement effect of the soils, a case history of soft soil treatment of a major road construction in a city of Xiamen is presented in this paper. Flat dilatometer test method was used to conduct insitu tests in various soil layers within the treatment range. The strength and deformation parameters before and after treatment were obtained, and their variation patterns were studied to evaluate the treatment effect of the soft soils. The results indicate that the material index can effectively classify the properties of each soil layer, and the strength, modulus, and other parameters obtained from the test interpretation can accurately reflect the vertical changes in the properties of the soil layer; Before and after the reinforcement, the material index of the soil layer changes slightly, with a slight increase, while the strength parameters (undrained shear strength) and deformation parameters (lateral expansion modulus, lateral limiting modulus) of the soil layer show different degrees of increase, indicating that the floating soil mixing column treatment has obvious reinforcement and improvement effects on the strength and stiffness of the soft soils. The ratio of strength and deformation parameters of silt, muddy silty clay, and muddy clay before and after reinforcement is greater than 3.0, while the ratio of strength and deformation parameters of the fine sand and the silt interlayer and the fine sand before and after reinforcement is around 2.0. The increase in strength and deformation parameters of soft soil is independent of depth.

Key words: Dilatometer Testing Method, Soft Clay Treatment, In-situ Test, Constrained Compression Modulus, Compression Modulus, Undrained Shear Strength