Purevsuren Munguntsetseg

A study on reliquefaction of cementitious sand

Hirofumi Toyota
 
In recent earthquakes, many liquefaction phenomena have been observed at the same locations where liquefaction had occurred in the past. As a result, a great deal of damage was caused to lifelines.

In general, when liquefaction occures, the liquefaction strength is considered to increase because the soil becomes denser through drainage of pore water. However, reliquefaction has been soemtimes occurred at smaller earthquakes than the past earthquakes. This suggests that reliquefaction may occure easily because the cementation of the soil is broken by the first liquefaction. Factors that affect the liquefaction strength of soil are density, history effect, chemical reaction, and aging effect. The aging effect is a phenomenon in which the mechanical characteristics of soils change through time.

In this study, we focus on the aging effect. Therefore, a small amount of cement was added to the sand sample to give a cementation effect, which reproduces the aging effect. The objective of the study is to clarify the liquefaction characteristics of the sand reproduced aging effect and the mechanism of reliquefaction, focusing on the change of sand cementation by liquefaction.

Two types of liquefaction were defined in the study. First, liquefaction was judged when the mean effective stress p'=0 kPa. This is reffered to as small liquefaction degree, where double amplitude strain are about 1-2%. Second, liquefaction was determined when double amplitude strain reaches 5%. This is defined as the large liquefaction degree.

The followings are the conclusions obtained from this study. 
1) The case of small liquefaction degree: The reliquefaction strength was greater than the liquefaction strength in the cementitious sand. Therefore, reliquefaction is unlikely to occur in the ground.
2) The case of large liquefaction degree:  The reliquefaction strength was smaller than the liquefaction strength in the cementitious sand.