EXPERIMENTAL RESEARCH ABOUT SUBSIDENCE COUNTERMESURE OF BREAKWATER TO TRENCH TYPE EARTHQUAKE MOTION

Abstract

 Shake table tests of a large model in 1g gravitational field were conducted to confirm performance of subsidence countermeasures for breakwaters based on the replaced sand layer during a trench type earthquake motion. As countermeasures for existing breakwaters, sheet pile method and solidification method which do not improve the relaced sand layer just under the caisson were adoped. Forthermore placing rubble on the back of the caisson as the scouring protection for tsunami was adapted. It is difficult for all countermeasures to prevent subsicence completely as a result of the shake table tests because all countermeasures do not improve the replaced sand layer under the foundation. However, even if placing rubble on the back of the caisson, delay of the time when excess pore water pressure rises and shortening of the period by the increase of liquefaction resistance by the increase of effective overburden pressure showed that the amount of subsidence could be reduced compared with the case without countermeasure.