Application of the generalized scaling law to Saturated ground

Abstract

"Modeling of models"の手法を用い, 動的遠心模型実験に用いられる拡張型相似則(Iai, et al. 2005)の適用性を検討する。実物の100分の1の飽和砂質水平成層地盤を対象に, 遠心加速度を5gから70gに変化させ実験を行う。模型地盤に対し, プロトタイプスケールで最大入力加速度振幅2.5m/s2と3.1m/s2, 振動数0.65Hzの正弦波を与えた。いずれの実験ケースにおいても, 振動中の応答加速度, 水圧の挙動については, プロトタイプ換算値でほぼ一致した。しかし, 振動後の過剰間隙水圧の消散過程において, 10g以下の低い遠心加速度を用いた場合に, 50g以上の高い遠心場の場合と比較して, 消散時間が4倍以上長くなる現象が見られた。低い遠心場では, 有効拘束圧が小さいため地盤の弾性係数が小さく, 圧密理論から予測されるように, 圧密時間(=水圧消散時間)が長くなるものと推察される。

A series of centrifuge model tests are conducted under the scheme of the modeling of models technique to find issues on the generalized scaling law for dynamic centrifuge tests (Iai et al., 2005). In a series of dynamic tests on a flat, saturated sand layer of 1/100 scale, four different centrifugal accelerations from 5 g to 70 g are employed on the scaled models for which the prototype is uniquely given. The models are exposed to sinusoidal input accelerations with 0.65 Hz and amplitudes of 2.5 m/s2 and 3.1 m/s2 in prototype scale. For response during shaking, nearly identical accelerations and excess pore-water pressure buildups are recorded for all the cases in the prototype scale. Discrepancies are found on surface settlements and duration time for dissipation of excess pore-water pressure. The major causes of the discrepancy may be (1) the duration time for the initial consolidation, (2) small value of the shear modulus due to low confining stress in model ground under low centrifugal acceleration, and (3) reduced permeability due to adsorption of viscous fluids on sand particles.