| Project/Area Number |
17580218
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Irrigation, drainage and rural engineering/Rural planning
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| Research Institution | National Agricultural Research Organization |
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Principal Investigator |
YOSHIDA Shuichiro National Agricultural Research Organization, National Agriculture Research Center, Lowland Crop Rotation Research Team, Senior researcher (90355595)
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| Co-Investigator(Kenkyū-buntansha) |
ADACHI Kazuhide National Agriculture and Food Research Organization, National Agricultural Research Center, Research Team for Management in Paddy-Upland Rotation Systems, Chief researcher (80355594)
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| Project Period (FY) |
2005 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥3,180,000 (Direct Cost: ¥3,000,000、Indirect Cost: ¥180,000)
Fiscal Year 2007: ¥780,000 (Direct Cost: ¥600,000、Indirect Cost: ¥180,000)
Fiscal Year 2006: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2005: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Keywords | Soil shrinkage / Soil Cracking / Crack Tin Opening Angle(CTOA) / Finite Element Method(FEM) / Coupled analysis / 土壌の乾燥亀裂 / 亀裂先端開口角 / J積分 |
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| Research Abstract |
Mechanics of crack formation were described using Crack Tip Opening Angle (CTOA) measured with fractography soil were used. Fracture testing used deep-notch bend specimens formed by moulding a mixture of Ca-bentonite and silica sand, and a paddy soil at the liquid limit into rectangular bars, equilibrating to soil water suction ranging from 5 kPa to 50 kPa (with some 50kPa specimens wetted to 5kPa), and inserting a flaw 0.4 x specimen thickness. The growth and geometry of the cracks were quantified from a series of images. CTOA measured during stable crack growth decreased with drying. CTOA decreased even further when specimens equilibrated initially to 50 kPa were rewetted to 5 kPa. These results suggested CTOA was primarily governed by the stiffness, although rewetting probably altered the capillary stresses in advance of the crack tip.
Vertical crack propagation was studied in a laboratory-scale model subject to shrinkage. Soil installed in a container was consolidated by compression pressure. After removing the pressure, a vertical flaw was formed at the center, and then the specimen was subject to water suction imposed to both sides made of permeable ceramics. Observed CTOA values were compared with those measured by the bending tests. CTOA values in shrinkage were similar to those in bending, suggesting it is practically sufficient to use CTOA obtained by the bending tests for the simulation of shrinkage-induced cracking.
A numerical model was developed based on the coupled mechanical and hydraulic analysis of soil. The model is consists of a main program which calculates the deformation of soil due to depletion of soil water, and a module which determines progress of the crack tip by referring to current and critical CTOA. Test runs of the model proved that the predicted crack depths were practically corresponded to those measured in the field where parameters for the simulation were obtained
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