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

根据本研究进行的离心模型试验，连续墙的加固使桩的弯矩降低到原来的一半左右。通过今年的实验，明确了这一强化机制。连续墙的压力面积大于桩的压力面积。因此，液化砂对连续墙的流动压力大于桩的流动压力。其次，由于连续墙的抗弯刚度比桩的抗弯刚度大得多，连续墙的加固使桩的弯矩减小。当液化砂土流动时，连续墙作为刚体运动，桩作为端部固定的悬臂梁运动。由此可见，地下连续墙必须安装到非液化层的足够深度。充分的安装通过地面承载能力产生连续墙的水平阻力。桩内流动压力和弯矩减小。但如果液化范围扩展到地下连续墙底部，地面承载能力消失，地下连续墙就失去了侧向流动的阻力。其结果是连续墙发生流动，对桩产生较大的受力影响。这就产生了较大的桩端弯矩。本文的研究结论如下：虽然连续墙对桩基础的加固对侧流的影响是足够的，但重要的是要在非液化层的足够深度上安装连续墙。

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.