Shoya Shirai

Effects of long-term consolidation on liquefaction strength of sands

Hirofumi Toyota

In the 2011 off the Pacific coast of Tohoku Earthquake, the damage caused by large-scale liquefaction and re-liquefaction during the aftershock has been reported. It has been well known that possibility of liquefaction becomes lower due to effects of aging in old reclaimed land that after several hundred years have passed from the construction. However, the mechanism of the aging effect has not been clarified because it cannot be considered that the solidification of sand particles occurs in several hundred years.
In this study, undrained cyclic triaxial test, bender element test and static penetration test were performed using saturated sand specimens having various consolidation times to clarify the mechanism of aging effect in sands. The mechanism of aging were discussed using the liquefaction strength, shear wave velocity and penetration resistance obtained from those experiments. Moreover, liquefaction strength of long-term consolidation was estimated from the number of cycles to liquefaction with an assumption of the same inclination of liquefaction curve with that of normal consolidation time. The liquefaction strength after 100 years was predicted using the ratio of liquefaction strength ratio between normal consolidation time and long-term consolidation.
The following conclusions were obtained.
1. Properties of liquefaction strength
・It was confirmed that Nc to long-term consolidation of Toyoura sand increased at 14 days and 28 days consolidations. Therefore, some factors for increasing the liquefaction strength might generate after 7 days consolidation.
2. Properties of shear wave velocity
・A obvious difference due to consolidation time wasn’t observed in Vs of each spacimen.
3. Properties of static penetration
・A obvious difference due to curing time wasn’t observed in penetration resistance of each specimen.
4. Increase of liquefaction strength
・Liquefaction estimation was carried out using the predicted liquefaction strength of 100 years later. The reclaimed ground has been judged as non-liquefiable ground under Level 1 ground motion after 100 years had passed. However, the ground has been judged as liquefiable ground under Level 2 ground motion.
・Compared to previous studies, the day when the liquefaction strength increases might be faster in denser sands.

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