側方流動を受ける群杭基礎の動的挙動

Abstract

液状化による側方流動地盤中の杭基礎の挙動について、遠心模型実験および数値解析により考察した。模型実験は40分の1の縮尺で、用いた杭の配置は3x3の9本群杭、杭間隔は杭径の3倍である。杭の上下端は固定とした。杭基礎を配置した飽和地盤表面に傾斜30度を設け、地震波を入力し液状化による流動を発生させた。実験より、流動初期には杭頭の変位は地表面の変位に追随しているが、最終的な杭頭の変位は地表面変位よりも小さくなった。これは杭の剛性が高く杭間を土がすり抜けるためである。この実験結果より2次元有効応力解析法の妥当性について検討したところ、地盤ばねを適切に評価することで、すり抜けの効果を再現することができた。

Results of a series of centrifuge experiments to study the dynamic response of pile foundations under lateral spreading were compared to the results of numerical analysis. Experiments were carried out under the centrifugal acceleration of 40 G. Piles in the model foundation were lined up 3 by 3 pattern with a spacing of three pile diameter, and both pile head and bottom were rotation fixed. Piles were placed in the inclined ground of saturated sands and applied lateral loads due to the ground deformation. The effective stress finite element analysis was conducted to simulate these experiments. Computed time histories of pile head acceleration and displacement were consistent with those obtained from experiments. However, much smaller surface ground deformation in simulation might cause small amplitude of bending moments. Some calibration in the numerical modeling may be required to have more consistent results on bending moments.