Can Soil Liquefy More Than Once? 

The video on the left was taken at a site where significant ejecta material was observed shortly after an earthquake. The presence of ejecta and sand boils indicated that liquefaction had occurred. At the time of observation, the material was partly drained, exhibiting a crust-like surface. Upon repeated tapping with the foot, pore-water pressures began to rebuild within the underlying layer, causing the material to behave in a fluid-like manner. This occurred because the effective vertical stresses temporarily approached zero as excess pore-water pressures were regenerated through repeated cycles of loading.

Although this was not a controlled laboratory test designed to study re-liquefaction of previously liquefied soils, it nonetheless demonstrates that a soil which liquefied once can liquefy again under suitable conditions. This does not imply that all previously liquefied soils will necessarily liquefy again; rather, it confirms that re-liquefaction is possible, and assuming otherwise without detailed laboratory and field investigation would be imprudent.