干拓粘土の乾燥履歴とスレーキングについて(I)

The slaking characteristic of the clayey soil when soaked is a very important physical property of soil structure, and is also the fundamental property to make use of in the improvement of clayey soils. In this report, the behavior of clayey soil on reclamatcd land in the water area was studied in various drying stages and also on the repeated action of drying and wetting. Namely, the clayey soil (muddy soil) sampled from the sea bottom destined for reclamation was prepared by kneading and moulding with water content of about the liquid limit, and was preliminarily dried to a given pF of the soil moisture, and observations were made on their slaking properties when soaked in the 20℃ distilled water. The slaking percentages after leaving the soil for 24 houres on the 5 mm sieve in the water　were calculated And then, the slaking percentages after receiving repeated actions of drying and wetting or the effect of salt concentration in the sample were also tested under the same experimental conditions. The experimental results are as follows : 1. The slaking percentages of clayey soil of the sea bottom differs considerably depending on whether the drying stages is below or above pF4 of the soil moisture. When below pF4 of the soil moisture, the drying brings decrease in the amount of slaking soil. And when drying becomes over pF4 of the soil moisture, rewetting brings in very loose soil structure and the great amount of slaking soil. 2. After receiving repeated actions of drying and wetting, the slaking behavior of the sample seemed to receive the influences of the soil bonding materials. The slaking percentages of the air dried sample which had 36% in the first rewetting cycle increased to about 40% when soaked after the 3 rd to 4 th repeated cycle. While the oven dried sample with only 0.4% slaking at first gets finally about 33% slaking after receiving 6 th cycle of the repeated actions of drying and wetting. 3. Of the sample which receive the repeated actions of air drying and wetting, when the salt from the sample soil prevented to dissolve to the surrounded water in the rewetting stage, the slaking percentage in the second cycle became 25%. This was a rather higher percentage than in the other cases.