Multiple liquefactions phenomenon gained much attention in the Geotechnical Engineering field after the 2011 Off the Pacific Coast of Tohoku Earthquake in Japan and Christchurch Earthquakes in New Zealand. It was found that not just liquefaction can appear twice, but also can appear multiple times at the same sites. In addition, the damage caused by the multiple liquefactions were often more severe than the damage caused by the single liquefaction. This issue raises great concern on the reoccurrence of liquefaction in the future great earthquakes.

So far, several pioneer works have been able to investigate soil behaviors during re-liquefaction. However, most of those studies were limited mostly up to 2 stages of liquefaction due to the limitation of the apparatus itself. In this paper, a newly developed apparatus, so-called stacked-ring shear apparatus, is introduced. This apparatus aims to investigate the soil behaviors not just during 2 stages of liquefaction, but also during multiple liquefactions, by applying cyclic shear loading under constant volume condition.

The stacked-ring shear apparatus has a unique feature as compared to the common type of ring shear apparatus. However, both of these types of apparatuses still have common drawback, which is excessive friction between the soil particles and the metal rings. In the current study, several attempts have been employed to reduce the amount of excessive friction within the specimen. First attempt was done by reducing the number of rings composing the stacked-ring from 31 rings to 11, 8, and 5 rings. The second attempt was done by layering the surface of the ring using frictionless coating material. It is shown that reducing number of rings (reducing specimen's height) is more effective than the use of frictionless coating. However, there exists a certain limit, at which the number of rings can be reduced. Below this limit, fair comparison cannot be made since fewer stacked rings tend to generate un-equal amounts of friction on each stage of multiple liquefactions.