Effect of environment change on the strength of cement/lime treated clays

The field strengths of cement/lime treated clays were investigated in the Ariake Sea costal lowlands.The deposition environment of the investigation location is reconstructed and compared to the present ground environment.The mechanism of the ground environment change and its effect on the strength of cement/lime treated soil are discussed.The strength development of improved soil using cement and lime in different curing environments was investigated in the laboratory for studying the effect of environment change on the strength also.It has been found that the strength deterioration of improved soil in deep mixing method is due to 1)the ground environment change due to the secondary oxidation which results in low pH value and high organic content,and 2)the formations of the porous structures result from the elution of the calcium ions.Also,it has been found that the initial strength increase of the improved soil is related to the dissolved silica and that the dissolution of the silica in clay minerals needs long time.When examining the longterm strength for preventing strength degradation,the effect of environmental change has to be considered.The importance of measuring pH and oxidation-reduction potential(ORP)of the ground for cement/lime solidification method is explained.