Study and prediction method development of the progressive failure of embankment and gentle slope caused by excess pore water pressure propagation

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Progressive delay failure, in which fill and gentle slope fails after main earthquake motion, is being paid attention. For example, during the 2003 Sanriku-Minami earthquake and the 2003 Miyagi-ken Hokubu earthquake, sandy fill slopes failed like a mud flow. It was clear that pore water played important role in the failure, because failed soils contained much water and behaved like a mud. In this study, we have tried to make clear the failure mechanism of such a failure and to develop the prediction method. It was thought that excess pore water pressure generated by the vibration play an important role and the propagation of the excess pore water pressure is the cause of delayed failure. The results of this study are summarized as follows;1. We proposed a new idea to evaluate the liquefaction potential of unsaturated sandy soils based on the undrained cyclic shear test and it was confirmed experimentally. From the results, the liquefaction mechanism of unsaturated soils is clarified.2. Based on the residual deformation after undrained cyclic shear test, it was found that the shear deformation was related to the dilatancy characteristics of soil. These results are applicable to the evaluation of residual deformation of liquefied soil.3. Field investigation method called Geoslicer was used to find the trace of liquefaction induced flow failure during the 1964 Niigata earthquake.4. Change of the suction and water content of earth embankment were monitored for two years. From the data, the evaporation and the water retention characteristics were studied.5. Case study was conducted using the dynamic response analysis code developed.