報告書番号

U03031

タイトル（和文）

強震時における飽和砂地盤中の杭基礎挙動に関する基礎的検討

タイトル（英文）

Some Aspects of Pile Foundation Performance in Saturated Sandy Ground during Strong Ground Motions

概要 （図表や脚注は「報告書全文」に掲載しております）

強震時における飽和砂地盤中の杭基礎挙動に対する地盤密度の影響を調べる目的で大型振動台実験を実施するとともに，応答変位法を用いて杭の耐震設計解析を行う際に考慮すべき荷重などについて検討し，以下の知見を得た．(1)地盤が全層にわたって飽和状態で，杭の先端がヒンジ，杭頭が固定の条件では，地盤密度によらず杭頭が設計上最も厳しい条件となり，それは地盤全体が液状化に至る直前で発生する．特に密な砂地盤では，強震時のサイクリックモビリティー現象により大きな上部工慣性力が作用することから，密な砂地盤におけるサイクリックモビリティー現象が杭の損傷に重要な役割を果たす可能性があることが示唆された．(2)強震動時において杭頭に対して最も厳しくなる状態では，上部工慣性力と地盤変位のピーク値がほとんど同時に発生し，この時に杭頭曲率もピーク値を示す．(3)応答変位法を用いて強震時における飽和砂地盤中の杭の耐震設計解析を行う場合には，杭に作用する荷重として上部工慣性力と地盤変位の両方を考慮する必要がある．

概要 （英文）

Large scale shaking table tests were conducted in order to compare the performances of the pile foundation in the saturated sandy ground with the various densities during a strong ground shaking and analytical studies were performed on the external forces which should be considered in the seismic design analysis of the pile foundation based on the ground deformation method. The following results were obtained through this study; (1)Irrespective of the sand density, most severe condition for the seismic design of the pile foundation occurred near the pile head in the case that the pile head was rigidly linked to the superstructure, while its tip was connected to the base by hinge. And this condition occurred just before the initial liquefaction of the saturated sandy ground. In particular, because the inertia force of the superstructure became larger due to the cyclic mobility in the dense sandy ground during a strong ground shaking, it was suggested that the cyclic mobility of the dense sand was possible to play an important role for the damage of the pile.(2)In the severe condition against the pile head, peak values both of the inertia force of superstructure and ground displacement occurred at the same time and the curvature of the pile head also exhibited the peak value at this time.(3)It was necessary to consider both the inertia force of the superstructure and the ground displacement as the forces acting on the pile in the seismic design analysis of the pile foundation in the saturated sandy ground during a strong earthquake based on the ground deformation method.

報告者

キーワード