IMPROVED SOIL

PROBLEM TO BE SOLVED: To inexpensively provide improved soil by mixing and agitating at least a specified amount of soil and sand and a specified amount of crushed recycled concrete on clay in remaining excavated soil. SOLUTION: Clay is selected and sampled from a large amount of remaining soil produced by excavation, 40-50% (weight) of soil and sand and 10-30% (weight) of crushed recycled concrete are mixed and agitated for 30-40% (weight) of the clay, after primary crushing is performed by a jaw crusher, further secondary crushing is performed by an impeller breaker, next, agitation is performed by an agitator, and improved soil in which the clay, sand and crushed recycled concrete are sufficiently mixed is obtained. Since the improved soil is excellent in strength stability and moisture absorption, it does not collapse and depress even when a long period elapses in the case where it is used for refilling of an excavated part, and various buried underground facilities can be safely and surely supported and protected. Furthermore, since inexpensive crushed recycled concrete is used, it is economical.