Response of a silty sand centrifuge deposit to repeated Earthquakes

The estimation of liquefaction potential of soil deposits is mainly based on field liquefaction triggering charts based on the Seed and Idriss Simplified Method. Currently, these field liquefaction triggering charts seem to be generally conservative, as they do not take into account factors that tend to increase the liquefaction resistance of natural sand deposits located in seismic areas. The work presented in this paper incorporates data from the field, as well as centrifuge experiments performed at RPI. The experimental work involved simulating several decades to a century of earthquake events applied to a 6-m uniform silty sand deposit. The results show that repeated earthquake shaking generally has the effect of increasing the liquefaction resistance of soil deposits over time. This increase in liquefaction resistance does not seem to be fully accounted for by the simultaneous increase in the shear wave velocity of the soil. In other words, sites that have been subjected to hundreds of small earthquakes as well as some larger liquefying events may not liquefy again unless they are subjected to very intense earthquake shaking.