Abstract
Deep Mixing Method, a kind of in-situ admixture stabilization technique using quicklime, cement or their mixture as a binder, was developed in Japan and Scandinavian countries in 1970s. After then, a lot of research efforts have been performed on the strength characteristics of treated soil, interaction of treated and surrounding soils, development of new binder, development of new execution machine and technique, establishment of design procedure, and so on. The method has been widely applied to improve many varieties of soils such as soft alluvial clay and organic soil in many countries. However, long term property of treated soil is not throughout investigated.
Authors have kept two columns of in-situ treated soil with quicklime underground more than 27 years in order to investigate their long term property. Laboratory tests were carried out on one of them at 11 and 27 years' curing periods in order to investigate the long term change in the treated soil property. In the tests, unconfined compressive strength, wet density, water content and Calcium content were measured. For the 27 years' curing soil, needle penetration tests were also carried out to investigate the durability of the outer surface of treated soil. The series of the tests reveal that the treated soil cured for 27 years has gain three fold strength of original treated soil.
