Abstract: The area replacement ratio of the composite soil is the most critical parameter in estimating the bearing capacity of composite foundation. To solve the computational problem of area replacement ratio involved in composite soil treatment design and professional geotechnical engineer examination, especially the computational relationship among area replacement ratio and soil three-phase indexes. Based on the in-depth study of the concept and computation method of area replacement ratio, this paper presents the composite soil with reinforcement body (column) having the effect of compaction as the case history. The basic conversion relationship of soil three-phase indexes is briefly introduced. The main concept of the constant dry soil mass among columns before and after the soil treatment is presented. This paper also discusses and deduces the computational relationship among the area replacement ratio, void ratio, dry density and other three phase indexes of the soil under two working conditions. The accuracy of the derived results ate verified and the advantages in solving problems in the examination of professional geotechnical engineers. The relevant research results are helpful to the design practitioners of composite soil engineering and the examinee of the professional geotechnical engineers in calculating the area replacement ratio.

Key words: Composite Soils, Replacement Ratio, Void Ratio, Dry Density, Constant of Dry Soil Mass, Computational Relation