2026 Volume 75 Issue 1 Pages 31-36
The deep mixing method is the technology of improving soft ground by adding a stabilizer to soft ground and forcibly mixing the target soil and the stabilizer to create a strong foundation for relatively deep depths. Most of the improved bodies in general deep mixing methods are created using mechanical mixing methods, and the cross section of improved body (columnar improved body) has a uniform across cross section injection rate of stabilizer within the improved body. We are developing a method of constructing the cylindrical improved body with variable stabilizer injection rates within it. With this method, we can construct a column efficiently by lowering the stabilizer injection rate in the center and increasing the injection rate on the outer side. The construction of a cylindrical improved body utilizes a hybrid technology that combines the mechanical mixing method, in which high-concentration stabilizer slurry is injected under high pressure into the outer periphery of the body using special mixing blades, and the high-pressure jet grouting method. To confirm the effectiveness of the developed cylindrical deep mixing method in improving soft ground that we are developing, we conducted experimental and analytical studies, comparing it with column cross-sections of conventionally a improved body. Specifically, we performed element tests and numerical analyses using elastic-plastic FEM. This paper reports the results obtained from these tests and analysis, and discusses the improvement effect of the cylindrical improved body. Consequently, we were able to confirm that the unconfined compressive strength of the cylindrical improved body is about 20% higher than that of columnar improved body when the same amount of stabilizer was used. The superiority of the cylindrical improved body was also confirmed by the FEM analysis results.
