Tomoya Matsuoka

Relationships between shear wave velocity and liquefaction strength in sandy soil with stress history

Hirofumi Toyota

The surface wave method, which can be investigated the foundation structures using wave propagation characteristics under non-destructive condition with low cost, have attract interest in the field of ground investigation in recent years. A foundation assessment method using this method has been developed because shear wave velocity, Vs, and N-value have high relations with soil properties. A non-cemented and loose liquefiable sandy ground is treated in this study. The experiments were conducted to obtain the relation between Vs and liquefaction strength ratio, RL, using specimens with over-consolidated and shear stress history in the laboratory. Paying attention to the effects of stress history on Vs, performance of Vs as a parameter of liquefaction assessment was experimentally evaluated. The results obtained from the study are summarized as follows:
1. Although RL increased with stress histories acting to the specimens, Vs did not change with the stress histories. This fact was approved under any type of stress history. Therefore, it is difficult to recognize the stress history of the ground from information of only Vs.
2. Accuracy of a liquefaction judgment using Vs is very low because the judgment sometimes changes by several ranks when the ground is subjected a stress history. It is necessary for accurate prediction of liquefaction to extract undisturbed sample and to conduct experiments for liquefaction.
3. Liquefaction strength in 20 loading cycles has usually used for liquefaction assessment. However, the liquefaction strength in 100 loading cycles would be better to evaluate liquefaction phenomenon in the case of massive earthquakes, which have long duration of the shock.