Centrifuge model testing on reliquefaction characteristics of sand

Abstract

Soil can liquefy more than once (reliquefaction) when earthquakes occur in succession. A distinctive characteristic of soil reliquefaction behavior is that reliquefaction resistance may be lower than the first liquefaction occurrence, despite an increase in soil density caused by the drainage of groundwater; this characteristic has been proven in some previous laboratory and 1g shaking table tests. The study presented in this paper addresses an attempt to verify whether this decreasing tendency of reliquefaction resistance still exists in centrifuge model tests, which can simulate the gravitational stress of the actual ground under ng conditions. Moreover, the effects of two essential factors including grain size characteristics and the magnitude of the earthquake motion on the reliquefaction behaviors were investigated. The testing results demonstrated that the reliquefaction resistance tends to decrease in terms of the development speed of excess pore water pressure (EPWP), which is because the ground can reliquefy more quickly in the 2nd and subsequent shaking events than in the 1st shaking event. However, the ground settlement caused by the first liquefaction is still larger than that caused by subsequent reliquefaction, which indicates that the ground density still plays a significant role in determining the ground settlement. For the same input motion, the tendency of the EPWP development speed to increase during reliquefaction is more remarkable in medium-coarse sand than that in find sand. For the same sand, different input motions can cause a similar decreasing tendency in reliquefaction resistance for the 2nd shaking event. However, from the 3rd shaking event on, the enhanced effect of reliquefaction resistance due to the increase in ground density is more significant for a smaller input motion.