非排水せん断による液状化の原因となる過剰間隙水の変化

Abstract

本研究では、非排水条件における飽和土塊の液状化崩壊に必要な間隙水圧の変化予測モデルを評価した。モール・クーロン破壊基準おける土のせん断抵抗が、これと等しくなる時に発揮されるしきい間隙水圧が液状化崩壊した試料で示された。崩壊性地すべり地の滑落崖の試料を用いて様々な条件下で試験し、崩壊後に示される数秒間のせん断抵抗が土の密度を発達させた。しきい間隙水圧によりせん断開始直後に液状化した試料は、崩壊以前にもダイレタンシー傾向の強度が得られた。

A theoretical model predicting the pore pressure change necessary for liquefaction failure of saturated soil masses in undrained condition is assessed. It is shown that a threshold pore pressure, uc, derived from the Mohr Coulomb failure criterion when pore pressure at failure is equal to the corresponding shear resistance is enough to initiate liquefaction type of failure in sandy masses. Loading tests to failure on source-area sandy soils from a catastrophic landslide location, undertaken to verify the model, show that under definite conditions of loading, a threshold state, characterized by the equality and subsequent constancy of pore pressure and shear resistance from a few seconds after the commencement of shearing until failure, develops in the sands at a given density. Samples in which the threshold pore pressure was exceeded readily liquefied while those in which the pore pressure built-up was below the limit gained strength by tendencies to dilate. This paper demonstrates that while the stability of a slope founded on sandy soils may be breached when the pore pressure exceeds a certain limit, it is possible to make estimates of the limit. It is shown that where such estimates are accompanied with adequate field measurements of pore pressure, the efficiency of landslide prevention projects may be enhanced because only slopes whose stability is proven to constitute a real public threat are reinforced and reinforced adequately.