YAPA LAKSHIMA KALANI

Liquefaction and reliquefaction strength of overconsolidated sand considering orientation of sand particles

Hirofumi TOYOTA

Soil liquefaction is one of the most significant geotechnical hazards associated with earthquakes, causing considerable damage to infrastructure and ground deformation. In addition to the liquefaction history, soils may experience reliquefaction during subsequent seismic events, making it important to understand the factors influencing both phenomena. Natural sand deposits, such as sand dunes, are often formed by aeolian processes, resulting in preferred particle orientations. Furthermore, anthropogenic modifications, including excavation and ground leveling, may change the original particle arrangement and the stress conditions within the soil mass. Therefore, effects of particle orientation and stress history are considered to be important for liquefaction study.

This study examines the liquefaction and reliquefaction strength of overconsolidated sand incorporating with the orientation of sand particles. Triaxial tests were conducted on Toyoura sand specimens prepared at a relative density of 40% with particle orientations of 0��, 45��, and 90��. Here, two stress-history conditions were considered: normally consolidated (OCR = 1) and overconsolidated (OCR = 6). For the overconsolidated condition, specimens were subjected to a higher consolidation pressure and subsequently unloaded to simulate the stress history of natural cutting or excavated ground. The testing program consisted of consolidation, liquefaction, reconsolidation, and reliquefaction processes. Microscopic image analysis was also performed to examine changes in particle arrangement before and after liquefaction.

Experiment results indicate that particle reorientation occurs after the initial liquefaction under normally consolidated conditions, resulting changes in soil structure and influencing subsequent reliquefaction behavior. The results further show that overconsolidation increases liquefaction resistance from the initial liquefaction because of the effects of stress history, which enhanced soil stiffness. However, the reliquefaction response of overconsolidated sand reduced the liquefaction resistance in comparison with the initial liquefaction resistance. The findings suggest that both particle orientation and stress history play important roles in controlling liquefaction behavior. Finally, the study contributes to a better understanding of the liquefaction assessment of overconsolidated sand and provides useful insights for evaluating liquefaction hazards in natural and modified sand deposits.