2007 Fiscal Year Final Research Report Summary
Development of novel ground improvement technique of soil desaturating by air injection
| Project/Area Number |
17360227
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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 | Ehime University |
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Principal Investigator |
OKAMURA Mitsu Ehime University, Graduate school of science and engineering, Associate Professor (50251624)
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| Co-Investigator(Kenkyū-buntansha) |
MORI Shin-ichiro Ehime Univ, Graduate school of seience and engineering, Associate Professor (10304643)
TAKEMURA Jiro Tokyo Institute of Tech, Graduate school of science and engineering, Associate Professor (40179669)
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| Project Period (FY) |
2005 – 2007
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| Keywords | Seismic retrofit / Liouefaction / Foundation soil / Unsaturated soil / Multi phase flow analysis / Triaxial test / Centrifuge test |
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| Research Abstract |
Measures preventing earthquake-induced soil liquefaction are of significant importance to mitigate the liquefaction hazards. However, execution costs of currently available technique are generically expensive. An air-injection technique may be a simple, inexpensive alternative-this leads the saturated soils to the desaturated by injecting pressurized air bubbles, resulting in a higher liquefaction strength and the lower susceptibility This project aims at investigate Mowing items which are essential to develop a novel liquefaction countermeasure technique of soil desaturation by air injection.
(1)Influential factors of the liquefaction resistance of partially saturated sand are derived from theoretical consideration and effects of the factors are examined through a series of triaxial tests. It was confirmed that the degree of saturation has a significant effect on the liquefaction resistance. It also appeared that the liquefaction resistance depends on the initial confining pressure and
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the initial pore pressure; the higher the confining pressure and the lower the initial pore pressure, the higher the liquefaction resistance of partially saturated sand. A unique relationship between liquefaction resistance ratios and the potential volumetric strain was found, which enable to estimate the liquefaction resistance of partially saturated sand with the effects of the three factors taken into account.
(2)A series of centrifuge tests was conducted to investigate seismic behavior of desaturated soil-structure system and effects of desaturation as a liquefaction countermeasure technique. It was confirmed that settlements of the structure on partially saturated sand is much smaller than that of the saturated sand.
(3)A series of model tests that simulate air injection into saturated soils using air-injection probes, was conducted to investigate the desaturation mechanism during air injection It was found that the evolution of desaturation is strongly controlled by the vertical and horizontal permeabilities of the soil as well as the injection air pressure. The numerical analyses using a multiphase flow simulator is conducted to describe the evolution of the soil desaturation obtained from the measurements, and to examine the applicability of the model as a prediction tool enabling the evolution of desaturation in situ to be followed with time and space. Predictions show a good agreement with the measurements regarding the rates, magnitudes, distribution of degree of saturation, and airflow rates. Less
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