報告書番号

382041

タイトル（和文）

凍土の強度特性とクリープ特性におよぼす塩分濃度の影響

タイトル（英文）

EFFECTS OF SALINITY ON STRENGTH AND CREEP BEHAVIOR OF ARTIFICIALLY FROZEN SOILS

概要 （図表や脚注は「報告書全文」に掲載しております）

ヒーティング設備を設けない地下タンクにＬＮＧを貯蔵した場合，タンクに作用する凍結土圧とタンクの凍上現象の把握が重要である。本報告は，タンクに作用する凍結土圧を解析する際に必要な凍上の力学特性を塩分濃度との関係において調べたものである。（１）凍土中の塩分は，凍土の強度および変形特性に著しい影響をおよぼす。試験温度が共融点より高い－２０度Ｃの場合には，凍土の圧縮強度は塩分が増加すれば低下する。しかしながら，塩分濃度が１％よりも高い砂の場合には，温度が共融点よりも低くなると，強度は急激に増加する。（２）凍結した砂の強度は，氷飽和度が高い程大きくなる。（３）凍結した粘性土の強度は，土粒子をとり囲む不凍水膜の厚さと密接な関係にあり，不凍水膜の厚さが薄い程，強度は増加する。（４）凍結砂のクリープ変形量は，塩分濃度の影響が著しく，塩分濃度が高い程クリープ変形量は大きくなる。

概要 （英文）

IN RECENT YEARS,CONSIDERABLE INTEREST HAS DEVELOPED CONCERNING UNDERGROUND OR IN GROUND STORAGE OF CRYOGENIC LIQUIDS. IF AN LNG STORAGE TANK IS CONSTRUCTED IN THE GROUND,THE GROUND WILL BECOME FROZEN OVER THE YEARS. IN THIS STUDY,THE MECHANICAL PROPERTIES OF FROZEN SOILS ARE DETERMINED EXPERIMENTALLY. THESE PROPERTIES ARE REQUIRED TO ANALYZE THE GROUND FREEZING PROBLEM BY THE FINITE ELEMENT METHOD. SINCE LGN INGROUND STORAGE TANKS ARE OFTEN CONSTRUCTED ALONG THE COAST,TESTS WERE MADE ON FROZEN SOILS CONTAINING SALT. (1)IF FROZEN SOIL CONTAINS SALT,ITS COMPRESSIVE STRENGTH AND DEFORMATION CHARACTERISTICS ARE GREATLY INFLUENCED BY THE SALT CONTENT. WHEN SODIUM CHLORIDE IS USEDAS SALT CONTENT,AT TEMPERATURES HIGHER THAN -20DEGREE(EUTECTIC TEMPERATURE:-21.3DEGREE),THE COMPRESSIVE STRENGTH OF FROZEN SOIL DECREASES AS ITS SALINITY INCREASES. ESPECIALLY IN THE RANGE OF LOW SALT CONCENTRATION THE PERCENTAGE DECREASE IN STRENGTH IS HIGH. HOWEVER,IN THE CASE OF SAND,IF THE SALT CONCENTRATION IS HIGHER THAN 1% AND THE TEMPERATURE BECOMES LOWER THAN THE EUTECTIC TEMPERATURE,THE STRENGTH INCREASES SUDDENLY. (2)THE COMPRESSIVE STRENGTH OF FROZEN SAND IS RELATED TO THE DEGREEOF ICE SATURATION,FOUND BY TAKING INTO ACCOUNT THE INCREASE IN THE AMOUNT OF UNFROZEN WATER CAUSED BY SALINITY. THE HIGHER THE DEGREE OF ICE SATURATION,THE GREATER IS THE COMPRESSIVE STRENGTH. (3)THE COMPRESSIVE STRENGTH OF FROZEN COHESIVE SOIL IS RELATED TO THE THICKNESS OF THE UNFROZEN WATER FILM SURROUNDING THE SOIL GRAINS. THE LOWER THE THICKNESS OF THE UNFROZEN WATER FILM,THE GREATER IS THE STRENGTH. (4)THE AMOUNT OFCREEP DEFORMATION OF FROZEN SAND IS GREATLY INFLUENCED BY SALT CONCENTRATION. THE HIGHER THE SALT CONCENTRATION,THE LARGER IS THE AMOUNT OF CREEP DEFORMATION.

報告者

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