飽和砂地盤上の盛土の動的変形挙動

Abstract

飽和砂地盤上の盛土の動的変形挙動を調べるため，遠心模型実験，および多重せん断ばねモデルによる有限要素解析（FLIP）を行った．本研究で対象とした盛土は，堤体高さ3ｍ，天端と下端の長さが4ｍと11.5ｍ（実物スケール）である．また下部地盤の層厚は5ｍである．緩詰地盤を対象とした数値解析では地盤のN値=1に対応するパラメータを用いた場合に，天端の沈下量が実験結果と良く一致した．数値解析の結果，入力加速度が大きいほど，盛土下部の非液状化領域が大きくなり，それがくさびとなって周辺の液状化地盤を押しのけるため沈下量が大きくなるという，一見すると直感的ではない変形メカニズムが推察された．

Dynamic behavior of an embankment (3 m height) made of dry sand underlain by saturated sand deposit with 5 m depth are studied. Firstly, centrifuge experiments under 50 G are conducted. The relative density of saturated sand deposit is approximately either 30 % or 70 %. Sinusoidal input motions with various levels of peak acceleration amplitude are employed. Test results show that the maximum settlement was 1.4 m and 0.09 m, respectively, for loose and dense deposit. The amount of settlements for dense deposit are found to be proportional to the peak amplitude of input acceleration, while it may have a plateau for the case of loose deposit with increase of input acceleration amplitude. Following the centrifuge experiments, an effective stress analysis is carried out with the same prototype dimension of the experiments. The numerical analysis simulates well deformations and transient motions of the experimental counterparts. It is found that, in the analysis for loose deposit, when input acceleration increased, non-liquefied area underneath the embankment became large, causing larger non-liquefied wedge pushing liquefied soils aside.