| Co-Investigator(Kenkyū-buntansha) |
TAKAHASHI Akihiro Tokyo Inst. of Tech., Faculty of Eng. Research Associate, 大学院・理工学研究科, 助手 (40293047)
KUWANO Jiro Tokyo Inst. of Tech., Faculty of Eng. Associate Prof., 大学院・理工学研究科, 助教授 (30178149)
KUSAKABE Osamu Tokyo Inst. of Tech., Faculty of Eng. Professor, 大学院・理工学研究科, 教授 (40092548)
KITAZUME Masaki Port and Airfield Research Institute Head of Soil Improvement Lab., 室長
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| Research Abstract |
Short and long term behavior of soft clay improved by sand compaction piles with low replacement ratios, which is subjected to backfilled caisson loading, have been investigated through a series of centrifuge model tests. In the model tests the construction sequence from the installation of the caisson to the backfilling was simulated in-flight. Effects of replacement ratio, A_s, improvement width, SCP location and loading rate on the behavior of the caisson were studied. From the model tests the following were derived :
(1)Both during and after back filling, settlement of the caisson can be effectively reduced by higher replacement ratio. The settlement of caisson after backfilling is highly influenced by the settlement of the ground behind the SCP portion.
(2)Wider improvement area towards the fill is more effective in reducing the lateral displacement of the caisson both during and after backfilling and the degree of consolidation of clay part in SCP ground has a significant effect on
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the short-term lateral deformation.
(3)Using light-weight material as the back fill, both short-term stability and long-term settlement behavior can be effectively improved.
Furthermore, by using cavity expansion theory, theoretical equations on the cone tip resistance and shaft resistance were derived, in which the effect of replacement ratio of the SCP is taken into account as the stiffness of spring assumed surrounding a SCP. The effect of replacement ratio on the stiffness was investigated by pressure-meter tests and applicability of the derived equation was examined by cone penetration tests in the SCP with different replacement ratio in the centrifuge. From these studies, the followings were obtained :
(4)Subgrade reaction, k_h, of SCP is much smaller than the uniform sand with same density and the k_h, decreases with decreasing replacement ratio. As a result, the cone tip resistance and shaft resistance decrease with decreasing A_s.
(5)Comparing the calculated cone tip and shaft resistance with the observations, the possibility of the determination of fiction angle of SCP from the cone resistances was confirmed. Less
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