抄録
Several experimental studies were made on the shrinkage characteristics of clay soils, especially on the effect of the structural changes of these soils with change in the molding water content, and also the effect of the drying temperature (as a rate of drying). Test pieces of soil were molded with 5 different of molding water content and dried at the 3 drying temperatures of 30°C, 40°C and 50°C, respectively. Detailed measurements of horizontal and vertical strains were made and their shrinkage behavior in connection with soil structure was made clear by introducing the new conception of the coefficient of volumetric change.
The results are as follows;
(1) A drying temperature of 30°C did not have such a large effect on the shrinkage behavior but in case of a higher drying temperature, some effect was observed, which may be called the secondary shrinkage.
(2) There was a structural change in the soil test pieces in accordance with change in the molding water content, and its shrinkage constant varied linearly. An increase in the molding water content causes an increase in the shrinkage limit and decrease in the shrinkage ratio.
(3) There is a linear relation between the coefficient of particle orientation, which shows structural characteristic of clay and percentages of cubical contraction by drying. As there is a fixed ratio between percentages of horizontal and vertical shrinkage, it appears that the structural change of clay takes place in an orderly manner by drying.
The coefficient of particle orientation decreases with increase in the molding water content, and it tends to become a parallel orientation.
(4) Results of detailed observation on horizontal and vertical shrinkages are;(a) horizontal shrinkages are mainly caused by pF 2 to pF 4 of soil water, (b) vertical shrinkages begin with the start of drying and a higher molding water content causes a larger vertical shrinkage rate.
(5) From the point of view of the coefficient of volumetric change, there is some difference in the shrinkage behavior due to molding water content in case their horizontal and vertical shrinkage characteristics are the same and have the same parallel orientation. This indicates that there are some quantitative differences among the oriented soil particles.
