2004 Fiscal Year Final Research Report Summary
Behavior of pore water pressure and stability evaluation against seepage failure in earth slopes
| Project/Area Number |
15560432
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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 |
Geotechnical engineering
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| Research Institution | Aichi Institute of Technology (A.I.T.) |
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Principal Investigator |
NARITA Kunitomo A.I.T., Faculty of Engineering, Professor, 工学部, 教授 (90064956)
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| Co-Investigator(Kenkyū-buntansha) |
OHNE Yoshio A.I.T., Faculty of Engineering, Professor, 工学部, 教授 (00064931)
KIMURA Katuyuki A.I.T., Faculty of Engineering, Professor, 工学部, 教授 (70064954)
OKUMURA Tetsuo A.I.T., Faculty of Engineering, Professor, 工学部, 教授 (70078913)
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| Project Period (FY) |
2003 – 2004
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| Keywords | Centrifuge Model Test / Rapid Draw-down / Pore Water Pressure / Seepage Failure / Slope Failure / Saturate Unsaturated Seepage / Seepage by Rainfall / Slope Protection |
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| Research Abstract |
In order to study behavior of the residual pore-water pressure and its influence on slope stability in earth dams during a rapid draw-down of the reservoir water, centrifuge model tests were conducted on several model fills by realizing draw-down of the upstream water level under a constant centrifuge acceleration, in which small size transducers were installed in matrix for pore-water pressure measurement. Several different conditions to be supposed were set in the experiment to investigate influential factors on accumulation of the built-up pore-water pressure in embankments : that is, the case where the rate of draw-down is changed for the same type homogeneous embankments, the case where a thin impervious soil layer is set on the upstream face as an inclined core zone, and the case where a L-type drain is set to promote dissipation of pore-water pressure in the middle part of an embankment. Some failure tests, in which sliding failure is reproduced in the upstream slope, were also
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conducted to discuss instability of slopes caused by the increase of the residual pore-water pressure built up during draw-down. Concluding remarks drawn from the present study are summarized as follows : (1) In the case where the rate of draw-down of the reservoir water is high, drainage water from the interior to the up stream face is restricted even in a homogeneous dam, and the residual pore-water pressure develops in the upstream slope to have a large influence in slope stability. (2) In a dam with a thick impervious core zone, a discontinuous head difference appears in every state between the reservoir water level and the phreatic surface in the dam, due to little flow of drainage water to the upstream face. (3) Although the residual pore-water pressure reduces rapidly in the interior of an embankment by setting a L-type drain, it still shows high value in the surface part of the fill to the extent of the case without drainage facilities, and comparatively deep sliding failure passing through the crest appeared as the water level decreases.
Another series of centrifuge tests were done on the behavior of seepage uplift pore-water pressure acting on the base of a river dyke resting on a permeable soil foundation, and discussion was made on the influence of the uplift pressure on such seepage failures of embankment as piping and loss of bearing capacity. Analytical studies were also performed by use of the FEM saturated and unsaturated seepage analysis, and a method of stability evaluation of earth slopes was proposed, by taking into account of distribution of pore-water pressure along a sliding plane and that of hydraulic gradient in the fill, from both view points of sliding failure due to pore-water pressure and seepage failure (hydraulic fracture) due to concentration of hydraulic gradient. Less
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