Takaki Matsumaru

Three-Phase Seepage-Deformation Coupled Analysis about Unsaturated Embankment Damaged by Earthquake

AbstractThe 2004 Niigata-ken Chuetsu Earthquake in Japan caused serious damage to embankments. Considerable damage occurred in mountainous regions, and the recorded rainfall before this earthquake exceeded the annual rainfall. In this study, numerical simulations were performed to reproduce the damage and to investigate the effect of rainfall on seismic behavior. In the simulations, a three-phase (soil, water, and air) coupled analysis was adopted to consider the behavior of unsaturated soil, and a conventional elastoplastic constitutive model was used for unsaturated soil. The deformation of the embankments was quantitatively reproduced by incorporating rainfall in the seepage analysis before the dynamic response analysis, and it was found that heavy rainfall significantly affected the dynamic behavior. Furthermore, parametric studies of countermeasures showed that the embankments would deform as a result of poor-quality materials even if sufficient drainage or impermeable roadbeds were constructed.

Shaking Table Test of Embankment on Inclined Ground Affected by Rainfall

During the Nigata-ken Chuetsu Earthquake having occurred in 2004, a number of railway and road embankments collapsed in mountainous regions. It appears that the main reasons of these damages were inclined ground conditions and the rainfall caused by the typhoon just prior to the earthquake. In this paper, the authors performed shaking table tests of embankments on inclined ground affected by rainfall intended for evaluating the adverse effect of rainfall seepage on seismic resistance. We conducted two cases using permeable ground and impermeable one. Rainfall was poured into the embankment until confirming rise of degree of saturation and partial formation of water level. The shaking was conducted until the embankment collapsed with increasing the maximum acceleration. From two cases of shaking table tests; it was revealed that the seepage boundary conditions of the ground affected behaviors of the embankment. In the case without shaping of water level, the response of acceleration at the top of the embankment increased excessively and the embankment deformed to a shape of circular. On the other hand, in the case with shaping of water level, the embankment collapsed with flow, so the response of acceleration decreased during the shaking. Furthermore, the mechanism of stopping of increasing of pore water pressures during shaking was revealed.