Liquefaction resistance of a silty sand deposit subjected to preshaking followed by extensive liquefaction

The effect of extensive liquefaction on the liquefaction resistance of heavily preshaken saturated silty sand is studied using a centrifuge experiment. The base of a 6-m homogeneous deposit was subjected to a total of 91 shaking events of different horizontal base accelerations and durations. Three event types were used in alternating patterns: mild preshaking Events A, stronger preshaking Events B, and strong liquefying Events C. The experiment was divided in two stages. In Stage One, reported in a previous publication, 66 preshaking Events A and B, were applied. In Stage Two, which is the focus of this paper, 25 additional shakings were applied which included two Events C in addition to continuing the same pattern of Events A and B. Stage One resulted in a significant increase in liquefaction resistance of the deposit. In Stage Two, extensive liquefaction produced by Events C resulted in a dramatic immediate reduction in liquefaction resistance of the deposit to a level comparable to that before preshaking. These findings are consistent with other reported field observations and laboratory results.