1998 Fiscal Year Final Research Report Summary
Stability of deep excavation in soft clay deposits-Deformation and interaction with adjacent structure-
| Project/Area Number |
09045048
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| Research Category |
Grant-in-Aid for international Scientific Research
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| Allocation Type | Single-year Grants |
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| Section | University-to-University Cooperative Research |
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| Research Field |
Geotechnical engineering
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| Research Institution | TOKYO INSTITUTE OF TECHNOLOGY |
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Principal Investigator |
TAKEMURA Jiro Tokyo Inst.of Tech., Faculty of Eng.Associate Prof., 工学部, 助教授 (40179669)
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| Co-Investigator(Kenkyū-buntansha) |
TAKAHASHI Akihiro Tokyo Inst.of Tech., Faculty of Eng.Research Associate, 工学部, 助手 (40293047)
KOUDA Masayuki Tokyo Inst.of Tech., Faculty of Eng.Research Associate, 工学部, 助手 (10282823)
KUWANO Jiro Tokyo Inst.of Tech., Faculty of Eng.Associate Prof., 工学部, 助教授 (30178149)
KUSAKABE Osamu Tokyo Inst.of Tech., Faculty of Eng.Professor, 工学部, 教授 (40092548)
TAN Thiam-Soon National Univ.Singapore, Faculty of eng., Associate Prof., 工学部, 助教授
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| Project Period (FY) |
1997 – 1998
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| Keywords | open braced excavation / earth pressure / soft clay / centrifuge model tests / deformation / construction sequence / 3D effects |
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| Research Abstract |
In this study centrifuge model tests on vertical excavation in normally consolidated soft clay was carried out using a newly developed test systems in TIT and NUS.By TIT and NUS systems construction sequence in double propped wall open excavation and rectangular shape excavation can be properly simulated in flight respectively. The following conclusions were drawn.
(1) The assumption of undrained condition can be reasonably adopted for NC clay during excavation because of positive pore pressure generation due to shearing.
(2) Normally consolidated clay reached Rankine's active conditions at very shallow excavation depth before lower propping. The importance of strength anisotropy for the stability evaluation in open excavation was confirmed in the tests. The clay in the bottom of excavation reached its passive condition around the half of excavation depth. The deformation after this depth was mainly determined by the mechanical properties of sand, i.e., stiffness or stress-strain.
(3) Pro
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pping can prevent marked increase in the settlement ; however, it is very difficult to recover the settlement and deformation once it occurs by increasing the strutting force (i.e., preloading). Hysteretic and non-linear behavior of soil is considered to be one of the main reasons of the irrecoverable deformation.
(4) Difference in the settlement trough with different propping conditions mainly revealed near the wall, while for far away from the wall no much difference in the trough could be seen.
(5) The wall deflection was derived from the data of two laser displacement transducers at different heights and strains along the wall. Although some scattering was included due to the inevitable error in the deflection calculation, a non-linear relation was clearly obtained between mobilized strength and deflection.
(6) The corner constraint plays an important role in controlling wall and ground movement in an unstrutted 3D excavation. Increasing the thickness of the wall reduces the wall and ground movement. Less
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