Seismic Performance of Caisson Type Quay Wall with Lightweight Backfill

In order to improve the seismic capacity of a caisson type quay wall, lightweight backfill method is often used in practice. However, the interaction between the caisson and lightweight backfill is not yet clear due to its high complexity. In this study, a series of centrifuge shaking tests, in which a strong model box was used with the model ground made of relatively dense sand, was conducted to investigate failure mechanism, earthquake induced earth pressure, force equilibrium, etc. Width of the lightweight backfill was varied as a parameter. In the case with sand backfill, active failure in the backfilled sand occurred, while in the cases with lightweight backfill, two independent active failures occurred in the sand regions behind the lightweight backfill and caisson. Horizontal displacement of the caisson during seismic shaking was significantly decreased by lightweight backfill, because earth pressure between the caisson and backfill was reduced. Effect of the inverted trapezoidal lightweight backfill to decrease the horizontal displacement is much higher than that of the rectangular lightweight backfills, when the slope of the inverted trapezoid is milder than that of active failure surface in the sand.