Development of Method for Estimating Lateral Resistance of Pile Groups in Liquefied Soil during an Earthquake

自1964年新泻大地震以来，饱和砂土液化机理和土的抗震性能逐渐被人们所认识。然而，近年来，由于大地震引起的液化所造成的损害已被报道，例如1993年的北海道南西冲地震、1995年的兵库县南部地震、2000年的鸟取西武地震等。在兵库县南部地震中，从原海岸线到填海造地的广泛区域发生了大规模液化，以及建筑物下桩基的破坏。对桩基破坏的原因进行了研究。然而，许多不确定性，以建立横向承载桩支撑建筑物的设计方法仍然存在，特别是当考虑有效应力减少桩周围的土壤中，由于孔隙水压力增加，在地震期间。因此，我们设计并 关于我们 本文利用渗流降低试验砂层中有效应力的试验装置，进行了模型桩的侧向荷载试验，研究了作用在模型桩上的地基反力，得到了以下结论：1.在一定水平上，桩的侧向地基反力与桩的侧向位移呈双曲线关系;初始模量和双曲线的收敛性分别与地基侧向反力初始系数和地基侧向反力极限值有关。2.地基侧向反力初始系数和地基侧向反力极限值均随深度线性增加（即三角形分布），随有效应力的减小而线性减小。根据这些结果，我们能够提出一种新的桩基设计方法的基础上的地基反力分析，考虑在地震过程中的地面有效应力的减少。3.此外，还提出了基于三维理论的群桩基础分析，考虑弹塑性连续体和桩周土的极限侧阻力。少

The mechanism of the liquefaction in saturated sand and soil resistance during an earthquake has been gradually made clear since 1964 when the Niigata earthquake occurred. In recent years, however, the damages due to the liquefaction caused by the large earthquakes have been reported, for example the Hokkaido-nansei-oki earthquake in 1993, the Hyogoken-nambu earthquake in 1995, the Tottori-seibu earthquake in 2000, and so on. In the Hyogoken-nambu earthquake, the large-scale liquefaction occurred in the wide area from the former coastline to the reclaimed land, and the damages occurred in the pile foundation under buildings. The cause of damages of the pile foundations has investigated by some researchers. However, many uncertainties to establish the design method for laterally loaded piles supporting a building still remain, especially when considering effective stress reduction in soil around piles due to pore water pressure increasing during an earthquake. Therefore, we devised and … More made the appropriate test apparatus for decreasing effective stress in the test sand bed by using the seepage flow, and performed laterally loading tests in order to investigate the subgrade reaction acting on the model pile.The following points are found out from these studies :1.The lateral subgrade reaction on the pile at a given level is approximated by the hyperbola with respect to the lateral displacement of the pile. Then the initial modulus and the convergence of the hyperbola are related to the initial coefficient of the lateral subgrade reaction and the ultimate lateral subgrade reaction, respectively.2.Both of the initial coefficient of lateral subgrade reaction and the ultimate value increase linearly with depth (i.e. triangle distribution), and decrease linearly with decreasing the effective stress in the sand bed. From these results, we are able to present the new design method of pile foundations on the basis of the subgread reaction analysis which considers the reduction of effective stress in ground during an earthquake.3.Furthermore, the analysis for the pile group foundation based on the three dimensional theory, which considers an elasto-plastic continuum and the ultimate lateral resistance of the soil around the piles, is also proposed. Less