Field Observation of Long-Term Strength of Cement Treated Soil

Deep mixing method is a kind of soil stabilization technique using cement and/or lime as a binder, constructing treated soil columns, wall or massive block in soft ground. The method has been applied in practice since 1975. So far, many researches have been carried out to investigate mechanical characteristic of treated soil based on laboratory and field samples aged less than a couple of years. However, long-term change of mechanical, physical or chemical characteristic of treated soil is not entirely made clear yet. In this study, in-situ treated soil columns were investigated in detail. These columns, each having 1 m in diameter and 8 m long, were constructed by dry method of deep mixing about 17 years ago in a site in Hokkaido. The primary purposes of the study are two-fold; one is to investigate the long-term strength increase within the sound part of treated soil columns and the other is to investigate the possibility of deterioration at the periphery of columns. In the central portion of the columns, the steady strength increase after 17 years was confirmed. The leaching of Ca from treated to untreated soil was observed. However, the extent and magnitude of strength reduction at the periphery of the columns was very small at the present test site.