THE EARTHQUAKE-RESISTANT REINFORCEMENT OF PILE FOUNDATIONS WITH DIAPHRAGM WALL TO LATERAL FLOW OF LIQUEFIED GROUND

根据离心模型试验结果，地下连续墙加固后，桩身弯矩减小了一半左右。通过今年的实验阐明了这种强化机制。地下连续墙的承压面积大于桩的承压面积。因此，液化砂土对地下连续墙的流动压力大于桩的流动压力。其次，由于地下连续墙的抗弯刚度远大于桩的抗弯刚度，地下连续墙的加固使桩的弯矩减小。在液化桑迪地基流动时，地下连续墙作为刚体运动，桩作为端部固定的悬臂梁运动。这表明，地下连续墙必须安装到非液化层的足够深度。地下连续墙的充分安装利用了地基的承载力，产生了地下连续墙的水平抗力。桩内流压和弯矩减小。但当液化范围扩展到地下连续墙底部，地基承载力消失时，地下连续墙将失去对侧流的抵抗力。其结果是，地下连续墙流动和大的力影响桩。本文的研究结论如下：虽然地下连续墙对桩基的加固作用足以产生侧向流效应，但地下连续墙在非液化层中的安装深度是很重要的。

According to the centrifugal model experiment carried out in this study, the bending moment of the pile decreased to about the half by the reinforcement of the diaphragm wall. This reinforcing mechanism was clarified by the experiment on this year as follows. The pressure area of the diaphragm wall was bigger than that of the piles. Therefore, the flow pressure of the liquefied sand that affected the diaphragm wall was bigger than that of the piles. Next, the bending moment of the piles decreased by reinforcement of diaphragm wall because the bending rigidity of diaphragm wall is considerably bigger than that of the piles. The diaphragm wall moves as rigid body and the piles move as a cantilever beam of which the tip was fixed, when the liquefied sandy ground flows. This shows that the diaphragm wall must be installed to the sufficient depth of the non-liquefaction layer. The sufficient installation generated the horizontal resistance force of the diaphragm wall by the bearing capacity of the ground. And then, the flow pressure and the bending moment in the piles decreased. But if the range of the liquefaction spreads to the bottom of the diaphragm wall and the bearing capacity of the ground disappears, the diaphragm wall loses the resistance force for lateral flow. As the result, the diaphragm wall flows and large force affects the piles. This generated the large bending moment at the pilesThe conclusions of this research are as follows ; it is important to install the diaphragm wall to the sufficient depth to the non-liquefaction layer, though the reinforcement of pile foundation by the diaphragm wall is the sufficient effect for lateral flow.