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

通过离心试验，对填土式重力沉箱码头墙的抗震性能进行了评价。在沉箱模型上建立了3个水压力箱和3个土压力箱，测量了作用在沉箱与回填体边界处的水压力和土压力，认为这是由于地震力导致沉箱抗震性能的原因。在回收的回填土和沉箱下方的替换砂中安装了其他压力传感器，以监测液化的发生，液化也可能成为重力沉箱码头壁变形的主要原因。主要考察了前缘海床的物理性质、重力沉箱的形状以及重力沉箱所受地震波频率的影响。在30G离心条件下，对回填沉箱码头墙施加地震力。由于重力沉箱的存在增加了应力，充填体发生了部分液化，而沉箱下的置换砂则发生了部分液化。由于惯性力、置换砂的承载力下降和回填土动压的作用，重力沉箱向海方向移动，并向碎石丘正面沉降。在这种特殊情况下，沉箱的测量侧向位移约为40厘米。在考虑尺度效应的情况下，通过与小谷肯-南部地震的成果对比，发现推导出的位移是合理的。利用“LIQCA”代码对离心机模型试验的性能进行了数值分析。在对同一物料进行离心模型试验的基础上，结合离心模型试验的实测数据，合理确定了规范的参数。对数值分析和离心模型试验得到的加速度进行了过滤和比较。两种过滤后的加速度都显示出很好的匹配。虽然计算位移值略高于试验位移值，但数值结果能较好地描述试验位移值，尤其能较好地描述回填体中超孔隙水压力的产生/消散过程以及沉箱下替换砂的过程。研究结果表明，采用离心模型试验和数值评价方法可以较好地评价回填自重沉箱码头墙的原位性能。少

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