Strength characteristics of cement treated clayey and sandy soils in terms of overconsolidation ratio

The subject of this study is a cement treated soil, which is cement mixed soil. The cement treated soil has a number of advantages, for instance, the strength becomes larger than the soil before mixing. It also has tensile strength. Using these advantageous characteristics, in Japan, cement treated soil is widely used for waterfront projects to increase the bearing capacity of clayey ground and to prevent the liquefaction of sandy ground. From past studies, among with others, cement content and the type of soil are the most commonly recognized factors which affect the strength of cement treated soil. However, a main factor governing the strength has been unknown. The purpose of this study is to find out the main factor that affects the strength of cement treated soil. In this study, three kinds of cement treated soils are prepared by mixing cement with Ariake clay, Akita clean sand and Rokko decomposed granite and a series of undrained triaxial compression tests were performed. In this paper, based on the experimental findings, a concept to evaluate the strength of cement treated soil is discussed and a main factor governing the strength of cement treated soil is presented. The findings include: 1) The consolidation properties of cement treated clayey soil are similar to those of untreated clayey soil. 2) The strength properties can be characterized into normally consolidated region and overconsolidated region respectively in accordance with the consolidation yield stress. In the normally consolidated region, the failure envelopes are almost parallel to untreated soils and have an intercept depending on the cement content. In the overconsolidated region, the strength notably depends on the overconsolidation ratio irrespective of the cement content and the density of specimen. It is concluded that the consolidation yield stress and overconsolidation ratio are two most important factors in predicting the strength of cement treated soil.