飽和・不飽和二戸しらすの液状化強度および変形特性試験  [in Japanese] CYCLIC UNDRAINED TRIAXIAL TESTS FOR LIQUEFACTION STRENGTH AND DEFORMATION PROPERTIES OF SATURATED AND UNSATURATED NINOHE SHIRASU  [in Japanese]

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Abstract

東北地方太平洋沖地震において,飽和度が高い状況下でしらすからなる宅地盛土が泥流状に崩壊した.このメカニズム解明のために,当該箇所から採取した試料土を相対密度<i>D</i><sub>r</sub>: 60%~65%に再構成し,飽和状態と不飽和状態において,それぞれ100kPaで圧密後(<i>D</i><sub>rc</sub>: 70%~75%),液状化強度試験,変形特性試験を実施した.この結果,飽和状態のしらすは,7号硅砂(<i>D</i><sub>r</sub>: 60%)より液状化強度が小さくなった.また不飽和状態でも飽和度,過剰間隙水圧比が上昇し液状化に至ることが確認された.この液状化強度比は0.22となり,飽和状態に比べ1.5倍程度増加した.しかし,この場合でも被災時の加速度,地盤挙動を想定した<i>F</i><sub>L</sub>値は1を大きく下回った.<i>D</i><sub>r</sub>: 65%程度の飽和土,不飽和土の変形特性試験から求まった初期等価ヤング率はいずれも90MN/m<sup>2</sup>であった.

 Mudflow of earthfill composed of volcanic porous sandy soil called Ninohe Shirasu occurred during the 2011 Tohoku earthquake under high water content conditions. After sampling the soil and remolding it, cyclic undrained triaxial tests for liquefaction strength and deformation properties were conducted under saturated and unsaturated conditions. Not only saturated soil but also unsaturated soils were liquefied. The liquefaction resistance of saturated soil was less than that of standard sand. The liquefaction resistance of unsaturated soil was about 1.5 times greater than that of saturated soil, but the safety factor was low value under actual ground condition. The initial equivalent Young's modulus of the soil was about 90 MN/m<sup>2</sup>.

Journal

  • Journal of Japan Society of Civil Engineers, Ser. C (Geosphere Engineering)

    Journal of Japan Society of Civil Engineers, Ser. C (Geosphere Engineering) 72(3), 196-203, 2016

    Japan Society of Civil Engineers

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