2003 Fiscal Year Final Research Report Summary
Cause Investigation of Abnormal Settlement Phenomenon in Pleistocene Clay Layers by Experimental Examination of Clay Structural and Mineralogical Composition Changes
| Project/Area Number |
14350258
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Geotechnical engineering
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| Research Institution | Kobe University |
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Principal Investigator |
UCHIDA Kazunori Kobe University, Faculty of Agriculture, Professor, 農学部, 教授 (80111946)
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| Project Period (FY) |
2002 – 2003
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| Keywords | Strain Path Control / K_0 Consolidation / Triaxial Compression Test / Consolidation Test / Bender Element / Shear Modulus / Pleistocene Clay / Holocene Clay |
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| Research Abstract |
In this research, the K_0-consolidation characteristics of Pleistocene clay were examined using the strain-path controlled triaxial apparatus. The advantages of this test are described when compared with the conventional tests. Shear modulus was measured using bender element system to observe the change of particle structures indirectly. In addition, the particle structures were observed directly using the scanning electron microscope. The following concluding remarks can be obtained from this work.
1. The advantages of the strain-path controlled test were shown in the following : Strain and excess pore pressure in a specimen can control freely and can keep homogenous even in the large strain domain ; the drained mode and the K_0-consolidation mode of clays can be controlled exactly and their testing times can be shortened.
2. The result of this strain-path controlled K_0-consolidation test showed the very characteristic consolidation behavior of Pleistocene clay ; the void ratio decreas
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ed rapidly just after the pre-consolidation stress. This behavior is not apparent in a reconstituted kaolin clay sample. The K_0 value decreased to the pre-consolidation stress, then increased rapidly after that, and became a steady value. It seems that such results were due to structural change occurring in the clay just after the pre-consolidation stress.
3. The shear modulus G during the K_0-consolidation test gradually increased to 100 (MPa), then it almost kept constant after that. The void ratio of this changing point in G precisely agrees with the one changed rapidly just after the pre-consolidation stress. The main cause of this change G can be recognized to be structural changes of Pleistocene clay significantly just after the pre-consolidation stress.
4. The microscopic structure of Pleistocene clay was observed using the scanning electron microscope (SEM). A large number of diatoms destroyed were observed in the sample taken after a test although intact diatoms were observed in the one before a test. It can be considered that one of the causes for the rapid reduction of the void ratio just after the pre-consolidation stress is the frame of diatoms destroyed. In this research, the change of link structures of clay particles was not observed, which was considered as another cause of the rapid reduction of void ratio near the pre-consolidation stress. Less
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Research Products
(6 results)
