PURPOSE: To maintain required strength and to have a good permeability by adding and mixing a solidifying agent to the existing soil of a bed, presetting and curing for a required time until it reaches to a specific uniaxial compression strength, rolling pressing and tamping.

CONSTITUTION: According to the soil quality of viscous soil, Kanto loam layer, the suitable amount of cement type solidifying agent and the like is added and mixed to the existing soil of a bed. According to the hydration of the solidifying agent, soil particles are agglomerated. After the agglomeration is preset and cured for a required time until the uniaxial compression strength reaches to higher than 5kgf/cm2, rolling press and tamping are carried out by the use of a tire roller, macadam roller and the like. Required strength is thus generally maintained, and also permeability is improved through the gap of the formed agglomeration to enhance permeable coefficient.