メニュー

## 第75回

※今回は、採用4年目の特別研究員の研究成果を発表します。

Liquefaction refers to a sudden change in ground behaviour from solid-like to fluid-like. Induced by strong ground motion of an earthquake, soil happens to lose its strength and to start to flow, causing damages to structures on or under the liquefied ground.
Coupling between soil particles and pore waters is a key mechanism of liquefaction. Based on continuum mechanics, governing equations of soil displacement and pore water pressure are derived. Transition from a stable to an unstable solution of the governing equations is regarded as a source of liquefaction initiation. Stability analysis of the solution thus facilitates better numerical treatment of the initiation and development of liquefaction.
We carry out the stability analysis linearizing the governing equations. It is shown that dilatancy (shear deformation inducing volume change) changes the stability of plane waves of soil displacement and pore water pressure; the wave becomes unstable when the dilatancy ratio exceeds a certain critical value [1]. We further carry out numerical analysis that uses K computer for a spherical wave, developing a finite element method based on the particle discretization scheme that is suitable to compute soil particle detachment. It is shown that an unstable solution is captured; the dilatancy effect triggers and the detaching effect spatially expands the unstable solutions [2].
The loss of stability has been overlooked in the numerical analysis of liquefaction. For more rational prediction, therefore, it is necessary to develop a code which accounts for the stability. A finite element analysis that solves this problem is being developed.

[1]. J. Chen, H. O-tani and M. Hori, On Mathematical Stability Analysis of Liquefaction Considering Soil-Water Coupling, Journal of Japan Society of Civil Engineers, vol.70, No.2, I_641-I_648, 2014. doi: 10.2208/jscejam.70.I_641
[2]. J. Chen, H. O-tani and M. Hori, Stability analysis of soil liquefaction using a finite element method based on particle discretization scheme, Computers and Geotechnics, vol. 67, 64–72, 2015. doi: 10.1016/j.compgeo.2015.02.008