Misaki YOSHIDA

Study on reliquefaction of artificially cemented sand

Hirofumi TOYOTA

Some differences in damage of liquefaction and reliquefaction between aged and young reclaimed grounds have been reported in the 2011 off the Pacific coast of Tohoku Earthquake. According to those damage reports, liquefaction phenomena were confirmed at the same locations with the past liquefaction sites. Reliquefaction sometimes occurs in earthquakes smaller than the past earthquakes, which caused liquefaction. However, reliquefaction is considered to scarcely occur because the ground once liquefied becomes denser through drainage pore water. Thus, the mechanism of reliquefaction has not been clarified at present.
�@The addition of cement in sand has been widely used to imitate an aged sand in previous studies. Therefore, cementation effects, which is a factor the aging of sand, were examined using sand with small amount of cement: especially focused on the difference in mechanical properties between liquefied and reliquefied sands. Conducted tests are drained triaxial compression test under p�f constant condition, cyclic undrained triaxial test (liquefaction test), bender element (BE) test, and local small strain (LSS) test.
�@The obtained results in the study are follows:
1. Although the liquefaction strength did not increase in the specimens not greater than Cc = 0.3%, it increased in those not less than Cc = 0.5%.
2. Although the reliquefaction strength became smaller through the liquefaction history than the liquefaction strength at Cc = 0.0%, 0.3%, 0.5% specimens, almost no difference between the both strengths was observed at Cc = 1.0% specimen.
3. Although the relative density of the specimen increased by about 10% through the liquefaction history, the reliquefaction strength decreased. Therefore, the effect of the relative density on the reliquefaction strength was slight.
4. The shear stiffness of the reliquefaction specimen tended to decrease as the cement content increased.
5. It is difficult to estimate the reliquefaction strength from the shear stiffness because the decreasing trend in reliquefaction strength is different from that in the shear stiffness.