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Columnar inclusion is one of the effective and widely used methods for improving engineering properties of soft clay ground. This article investigates the consolidation behavior of composite soft clay ground using physical model tests under an axial-symmetry condition and finite element simulations by PLAXIS 2D program. It is found out that the final settlement and the rate of consolidation of the composite ground depend on the stress state (of what ?). For an applied stress much lower than the failure stress, the final settlement of the ground is insignificant and the consolidation is fast. When the soil-cement column fails, the stress on column suddenly decreases (due to strain-softening) meanwhile the stress on soil increases to maintain the force equilibrium. Consequently, the excess pore pressure in the surrounding clay increases immediately. The cracked soil-cement column acts as a drain, accelerating the dissipation of the excess pore pressure. The consolidation of the composite ground is mainly in vertical direction and controlled by the area ratio, the ratio of diameter of soil-cement column to the diameter of composite ground, a . The stress on column is low for the composite ground with high value of a , resulting in less settlement and fast consolidation. ) obtained from the physical model test on the composite ground can be used to approximate the rate of consolidation. This approximation is validated via the finite element simulation. The proposed method is highly useful for geotechnical engineers because of its simplicity and reliable prediction.

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Strength is often the most significant parameter in measuring the effect of soil improvement in geotechnical engineering practice. In this paper, a primary study is made of the variation in unconfined compressive strength of lime-treated soft clays under various practical conditions. There are three major factors that affect the strength NotationA w ratio of lime to clay by weight, both in dry state A w,max optimum lime content a rate of strength increment in the logarithmic t scale q shear stress q 0 strength of the untreated soil q max maximum unconfined compression strength q T0 strength at T ¼ 08C T curing temperature t curing time AE Aw material parameter describing the influence of lime content AE T material parameter describing the influence of curing temperature AE t material parameter describing the influence of curing time AE w material parameter describing the incremental rate of increase in strength with lime content