Minami Fujimoto

Liquefaction strength considering particle orientation of sand by shaking table tests

Hirofumi Toyota

Liquefaction and reliquefaction were observed mainly in the Kanto region during the 2011 off the Pacific coast of Tohoku Earthquake. It is believed that once liquefied, the soil becomes dense and less susceptible to liquefaction because pore spaces in loose sand decrease after the liquefaction. Although many cases of reliquefaction have been reported, mechanism of reliquefaction is still unclear. In this study, focusing on particle orientation of sand, it is investigated using shaking table tests how the liquefaction strength changes by particle orientation and how the particle orientation changes before and after liquefaction. The objective of this study is to evaluate reliquefaction strength using shaking table tests. The results will contribute to the elucidation of the mechanism of reliquefaction.
In this study, a completely sealed soil container was developed. Six test cases were conducted, including before and after liquefaction, with sample orientations of 0°, 45°, and 90°. In each case, particle orientation angles were measured from approximately 1,200 particles. Representative angles and concentrations were calculated using the Curray’s equations. The occurrence of liquefaction and liquefaction strength were estimated from the results of pore water pressure meters placed at 3 depths (5 cm, 14 cm, and 28 cm) before making model ground.
Findings are shown below.
-Liquefaction was confirmed by visual observation and results of pore water pressure.
-In all cases of 0°, 45°, and 90°, particle orientation approached to 90°by the liquefaction. In all cases, the degree of concentration increased after liquefaction, indicating that the randomly oriented particles became aligned after liquefaction.
-The particle orientation had slight different trend in the position of TOP, MIDDLE, and BOTTOM. However, the difference was not apparent in the depth direction.
-The results of pore water pressure can be used to compare liquefaction strength. In this study, it was not known whether the soil was fully saturated because of some leakage from the container. Therefore, liquefaction strength could not be determined from the results of pore water pressure this time.