土の異常挙動 : 加工硬化・軟化

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1. Introduction Recently many studies have been made on the trafficability of paddy fields for cultivators, tillers and tractors. The poor trafficability of paddy fields and volcanic ash soil roads for tractors was explained by the soil softening caused by soil remolding. The Kanto loam can become softer or harder, and the recovering degree ranges from 50% to 150% according to the given remolding condition which consists of remolding force, speed, the volume of the sample and its water content, etc. The mechanical properties of soil depend exclusively on the content and state of water, which is expressed in pF value. The pF is defined as follows: pF=long(-Δμ), Δμ=μ-μ_0 where μ is the the chemical potential of water in soil under the given condition and μ_0 is that of the water in bulk. 2. Samples and measuring method (1) Sample: The samples used in these experiments were taken from the Kanto loam, and stressed by the remolding force of about 0.3 kg/cm^2 for the period of 0.5 sec and 20 minutes. (2) pF: The samples, each weighing 5g, were saturated with water and centrifuged for 60 minutes under the constantly accelerating condition. (3) Stress relaxation: The stress relaxation of the samples was measured under the initial stress of 4%. (4) Strain retardation: The strain retardation of the samples was measured. The rate of strain per second was measured under a stress of 0.3kg/cm^2. 3. Results and discussion The pF value of the remolded samples was lower than that of the unremolded of the same moisture content. The pF value of the Kanto loam decreased remarkably by remolding, but that of air-dried samples was not. The difference in moisture content between the remolded sample and the unremolded of the pF value points to higher affinity to water of the remolded soil particles than those of the unremolded. The 1~2% strain may recover elastically, while the load is removed. The behavior of the samples can be treated as Burgers body practically, when the strain ranges from 2~5%. The strain of Voigt element in Burgers body corresponds to the deformation of soil granules with restrained water, while the Maxwell element prefers the flow among the granules around which free water behaves as lubricant. The creep curve of the samples after remolding shows the change in properties of elements in Burgers body. The rigidity of the soil decreases when the remolding time is less than 20 min, while the rigidity increases when the remolding time is over 20 min. The stress relaxation curve shows that when the remolding time is over 20 min, the relaxation time distribution shifts right, when the remolding time about 5 min, the curve shifts to the left.
社団法人日本材料学会の論文
1968-04-15

土の異常挙動 : 加工硬化・軟化

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