Reactive Measure Effects on River Dyke Instability and Adjacent Residences on Soft Clay Deposits after the Tohoku-Pacific Ocean Earthquake of 2011

抄録

This paper presents case histories of the instability of clay deposits beneath a loose sand layer induced after the Great East Japan Earthquake in 2011. As a reactive countermeasure against damage of this kind, the upper parts of existing river dykes were removed. Subsequently, sheet piles were installed immediately after the earthquake at the toes of river dykes to separate the influences of dyke instability on adjacent residences. Thereafter, the river dykes were returned to their respective original heights by surcharging the fills for dykes. To confirm the effects of those countermeasures, numerical analyses were conducted, combining both the computer codes for dynamic analysis of behavior during earthquakes with the code for static analysis of post-earthquake behavior. Results of numerical analyses agree well with variations of measurements of settlement with the elapsed time. Results indicate that the reactive countermeasures adopted herein work well for reducing the instability of river dykes and residences caused by the great earthquake.