ULTRASONIC-IMAGING VELOCIMETRY OF TRANSIENT LIQUEFACTION OF COHESIONLESS PARTICULATE MEDIA

The loss of shear strength of a water-saturated cohesionless particle bed, known as liquefaction, was imaged in real time using clinical ult rasound back-scattering in an effort to distinguish liquefied from set tled states in transient events. In the ultrasonic movies, the liquefi ed regions were found to be readily identifiable by their characterist ic small-scale random fluctuations, which are consistent with the know n phenomenon of particle diffusion in suspensions. The time sequences were analyzed and found to display an upward propagating interface sep arating settled from suspended regions, similar to the kinematic waves that arise in batch sedimentation, although their speeds were measure d to be up to an order of magnitude greater than the terminal velocity of an isolated particle. On the basis of this similarity, the solidif ication process that follows liquefaction was modeled using drift flux theory and the Richardson-Zaki correlation, which was found to give a good match with the high measured solidification wave speeds.