Study on the dynamic failure mechanism of a gravity caisson quay wall due to earthquake forces

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A series of centrifuge tests was carried out to assess the seismic behavior of a gravity caisson quay wall with reclaimed backfill. The caisson model has been constructed with 3 water pressure cells and 3 earth pressure cells on the back of it to measure the water pressure as well as the earth pressure acting at the boundary between the caisson and the reclaimed backfill, that is thought to cause the seismic behavior of the gravity caisson due to earthquake force. Other pressure cells were installed in the reclaimed backfill and the replaced sand beneath the caisson to monitor the occurrence of liquefaction that may also become a main cause for the deformation of the gravity caisson quay wall. Effect of the physical properties of the frontal seabed, the shape of the gravity caisson and the frequency of the sinusoidal wave applied as a seismic force on the gravity caisson was mainly examined. The seismic force was applied to the backfilled caisson quay wall under 30G centrifugal conditi … More on.Liquefaction occurred in the reclaimed backfill whereas the partial liquefaction took place in the replaced sand beneath the caisson because of the increase in stress due to the existence of the gravity caisson. Due to the inertia force, decrease in the bearing capacity of the replaced sand and the dynamic pressure of the reclaimed backfill, the gravity caisson moved seaward with a frontal subsidence into the rubble mound. The measured lateral displacement of the caisson was about 40 cm in this particular case. Considering the scale effect, the derived displacement is found to be rational by comparing the achievement reported from the Hyogoken-Nambu Earthquake.Numerical analysis was also carried out using the code "LIQCA" to describe the performance of the centrifuge model tests. The parameters for the code have been rationally determined on the basis of the laboratory experiments on the same material used in the centrifuge model tests and the measured data by the centrifuge model tests. The derived accelerations both from the numerical analysis and the centrifuge model tests were filtered and compared. Both filtered accelerations showed a good match. Although the calculated displacement slightly overestimated the experimental one, the numerical results can precisely describe the experimental ones, particularly the process of generation/dissipation of the excess pore water pressure in the reclaimed backfill as well as the replaced sand beneath the caisson. From those results, the procedure with centrifuge model tests and the numerical assessment adopted in this research has been found to be useful to assess the in-situ performance of the gravity caisson quay wall with the reclaimed backfill quite well. Less