In the case of structural construction of sheathing and cut-off wall within the city limit, the soil mixing wall engineering method is being employed because of least noise and vibration characteristics.
In this method, multi-shaft mixing auger machine are used to excavate the ground, mixing the soil with the blown cement milk from the auger axial, while the rectangular cement pile are continuously driven in. By using multi-shaft mixing auger, continuous soil cementing is possible, consequently raising its reliance as a sub-surface wall compared to that of the single auger. The strength of the soil cemented sub-surface wall weakens depending upon the kinds of soil encountered, and in the case of deep excavation, it cannot resist the soil pressure by itself, and thus the reinforcement by the H type steels at suitable intervals becomes necessary in actual practice. The important role of soil cement in this case are considered to be sheathing, rigidity and adherence to the H type steel. The soil cement may be efficient partially to improve bending rigidity, although it is usually neglected in design.
In order to clarify this point, an experimental study was performed on the effect of reinforcement for bending rigidity of the soil cement to the H type steel. It was found that this effect contributed about 20% to 30%.