Tertiary Creep Reproduction in Back-Pressure-Controlled Ring Shear Test to Understand the Mechanism and Final Failure Time of Rainfall-Induced Landslides

Abstract

人工降雨による室内地すべり実験によって福囿が1985年に発見した速度と加速度の間にべき関係があることがわかり、速度の逆数を用いた地すべり崩壊時刻の予知方法が開発され、広く用いられている。しかしその発現機構は未解明であり、土の三次クリープの発現機構を調べるため、背圧制御リングせん断試験を行い、豪雨時の地すべり発生時のすべり面の状態を再現した。試料には砂と砂・シルト混合試料を用いた。実験結果より、福囿の実験と同様の速度・加速度関係が得られ、べきの値の範囲も同程度ということがわかった。一方べき値と線形係数の対数の間に線形関係があることもわかった。

Fukuzono (1985) developed a method for predicting final failure time of a slope based on the findings from large scale flume test series that log of acceleration and velocity of surface displacement immediately before failure are proportional, d2x/dt2=A(dx/dt)α. He proposed a simple method for predicting failure time by plotting the inverse velocity of surface displacement (1/v). Yet, its mechanism is still unknown. To investigate the Tertiary creep mechanism in soils, a series of back-pressure controlled test on saturated sands were undertaken in ring shear apparatus. The tests were conducted under particular normal stress and shear stress with pore-water pressure changes to simulate the potential sliding surface condition in heavy rainfall. Sand and its mixture with clay material were used for specimen. Consequently, these tests could reproduce Tertiary creep to failure, in which similar log v-log α relationship and α value range was found. While, linear relationship of α and A values was found.