Journal of the Japanese Society of Soil Physics

A Consideration of the A- Line in the Plasticity Chart by Casagrande

Tatsuya Komoto

1990 Volume 60 Pages 2-5
Published: 1990
Released on J-STAGE: January 07, 2022

DOIhttps://doi.org/10.34467/jssoilphysics.60.0_2

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A hypothesis was performed on the A- line in the plasticity chart proposed by Casagrande for laboratory classification of fine- textured soils. By examining the results of tests on both the liquid and plastic limit published earlier on Bentonite, Illite and Kaolinite which are typical clay minerals, it was found that the relationship between the liquid limit (WL.) and plastic limit (Wp) could be expressed by the equation: WP 0.30WL +15.85 (WL≤120%) and Wp 69.8 ( constant) (WL>120%). On the basis of this linear relationship and the definition of the plasticity index (Ip), the following equation, which is closely similar to that of the A- line, was obtained as follows: IP 0.70 (Wl-22.6) (W≤120%).

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Evaluating Physical Condition of Kumamoto Soil Based on the “Non —Limiting Water Range” Concept

Seiko OSOZAWA, Shin Kozai, Toru Kubota

1990 Volume 60 Pages 6-14
Published: 1990
Released on J-STAGE: January 07, 2022

DOIhttps://doi.org/10.34467/jssoilphysics.60.0_6

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Soil Physical Properties related to root growth have been diagnosed by measuring separately air porosity, available water, gas diffusion, mechanical impedance etc. However, these factors interrelatedly and affect crop growth. The optimum physical condition for crop grow th may be that non- limited by soil water, aeration, and mechanical resistance. NLWR., proposed by Letey, seems superior diagnosis of soil physical conditions because of considering these factors comprehensively. These relationships were demonstrated using I)/Do 0.02 and soil strength 12kgf/cm2 as limiting values with main upland soils of Kumamoto prefecture. As the results, reasonable correspondance between N.LWR and experiential productivity.and correlation (r=0.71)between NLWR water content and root length of wheat were found.

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Erodibility of Compacted Soil

Katsutoshi Takuma

1990 Volume 60 Pages 15-23
Published: 1990
Released on J-STAGE: January 07, 2022

DOIhttps://doi.org/10.34467/jssoilphysics.60.0_15

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Particle breakage and effect on erodibility associated with compaction, were investigated. Erodibility of compacted mixed soil changed markedly along with the changes of permeability. The splash ratio (the volume of soil which splashed per unit volume of rainfall)and the amount of soil loss increased with the decrease of permeability. A peak was observed when the hydraulic conductivity was about 10-6cm s, followed by a rapid decrease. Erodibility characteristics of specific soils were as follows: there was a remarkable decrease of the splashing ratio in clayey soils, and an increase in sandy soils. Effect of compaction on the amount of soil loss was observed only in kaoline. Changes in the amount of soil loss in the Masa soil were not appreciable while in samples of other soils, soil loss increased by compaction. Compaction affected splash erosion in the case of clayey soils unlike in sandy soils. Permeability was related to erosion associated with rainfall and runoff. The effect of compaction was not significant in soils except for Kaolin, and, in perticular no effect was observed in volcanic ash soils.

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Soil Water Content in the Vicinity of Drying Cracks Having Roots in Clayey Subsoil.

Taiichirow Sato, Shuichi Hasegawa, Masahi Nakano, Tsuyoshi Miyazaki

1990 Volume 60 Pages 24-27
Published: 1990
Released on J-STAGE: January 07, 2022

DOIhttps://doi.org/10.34467/jssoilphysics.60.0_24

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Roots are often observed to grow in cracks formed in clayey subsoil. Water content gradients in these cracks, however, have not been examined under field conditions. We calculated the soil water content in the vicinity of the cracks in a field based in Richards' equation. Field experiments showed that there was no gradient when the average soil water content was -0.1MPa (Fig.1).Calculation showed that the soil water content gradient near the roots was very small for a soil water content exceeding -0.1MPa and that it became larger when the water absorption rate increased due to the high root density (Fig. 2). The results obtained confirmed that the soil water content gradient in the subsoil decreased uniformly regardless of the distance from the crack wall with roots.

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A Review on Thixotropic Researches in Soil Physics

Rokuro YASUTOMI, Katuya NAKAISHI

1990 Volume 60 Pages 28-33
Published: 1990
Released on J-STAGE: January 07, 2022

DOIhttps://doi.org/10.34467/jssoilphysics.60.0_28

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Irrigation and soil physical properties relevants to upland farming in Hokuso-daichi district

Hideyuki Takeda

1990 Volume 60 Pages 34-37
Published: 1990
Released on J-STAGE: January 07, 2022

DOIhttps://doi.org/10.34467/jssoilphysics.60.0_34

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[title in Japanese]

[in Japanese]

1990 Volume 60 Pages 38
Published: 1990
Released on J-STAGE: January 07, 2022

DOIhttps://doi.org/10.34467/jssoilphysics.60.0_38

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