| Research Abstract |
Several experimental studies have been carried out for studying void redistribution or water filmeffect such as in 1-D tube liquefaction tests, 1G shake table tests, laboratory cyclic shear tests, etc., which have yielded following major findings;
1)Sand deposits consisting of sublayers of different permeability are prone to develop post-liquefaction void redistribution; stable water films or transient turbulence, at sublayer boundaries, which may serve as a sliding surface in flow failure even after, the end of earthquake shaking. In sand deposits consisting of fine soil sublayers, void redistribution or water film mechanism can facilitate large flow displacements without mobilizing of dilatancy because the water films serve as a shear stress isolator, while a uniform sand deposit develop flow displacement only during shaking because of the dilatancy effect even when relative density is rather low.
2)In torsional undrained shear tests simulating sand sublayers beneath silt seams, a dila
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tive response, which is dominant in normal liquefaction tests, diminishes after the moment of water film generation, enabling large flow displacement to occur along it even when there is an initial shear stress in sloping ground. The non-dilative response appears immediately after the 100% pore-pressure build-up in loose clean sands with relative density around 40% or less, indicating that flow failure is very likely to occur once initial liquefaction starts.
3)In order to be able to take the void redistribution effect into account for design, more quantitative research is needed based on detailed case histories and sophisticated model tests on how to evaluate the initiation of flow for variety of soil conditions, how to predict the flow displacement, etc. Some advice on soil investigations, flow displacement evaluations and countermeasures are made in this paper in order to deal with this effect in practical problems now.
4)Collaborative research with University of California Davis revealed that two test results; by 1G shake table tests in Chuo University and by centrifuge tests by UC-Davis, give very similar results on the conditions for the involvement of water films in post-liquefaction lateral flow failures. Less
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