回転せん断試験による砂礫粒子の破砕特性評価  [in Japanese] EVOLUTION OF GRAIN CRUSHING DURING ROTARY SHEAR TEST  [in Japanese]

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Abstract

砂礫粒子の破砕特性を評価するために,粒子形状の角張った山砂と丸い川砂の二種類の試料を用い,回転数,回転速度,拘束圧を変化させて回転せん断試験を実施した.また,試験前後の試料の粒度分析を行った.その結果,どの条件でも十分にせん断が進行すれば,間隙比とせん断応力比,試料の粒度分析から得られるフラクタル次元は,同様の定常状態に達すること,粒子破砕およびそれに伴う体積圧縮は,回転の比較的初期の段階でより顕著に進行すること,回転速度の変化は今回の実験条件の範囲(0.21≦γ≦210(1/s))ではせん断応力,間隙比の変化に顕著な影響を及ぼさないことなどがわかった.その上で,二試料の単粒子破砕実験結果を基に,回転せん断試験の結果を系統的に評価できるマイクロメカニックスモデルの構築を行い,せん断に伴う体積圧縮は,間隙率とせん断ひずみが両対数で直線的な関係があること,圧縮が顕著に始まるせん断ひずみは,与える拘束圧と単粒子破砕強度の比によって表現されること示した.

To investigate the evolution of grain crushing during extremely large shear under constant confining pressure, a series of rotary shear tests was performed for two types of sands with various confining pressure, shear strain rate and total shear strain. Grain size distribution after the test was also measured for each sample. It turned out that (1) all the specimens reached an identical critical state with the same shear stress ratio, void ratio and gran size distribution described by a fractal (or power-law) distribution after a sufficiently large shear strain application, (2) the plastic compression occurred rapidly in the early stage of the test, and (3) the shear rate (from 0.21 to 210 (1/s)) did not affect the overall behavior. Based on such observation, a micromechanical model that connects the single grain crushing behavior with the bulk shear behavior was proposed. The model successfully described that a decrease in porosity with shear strain is a straight line in log - log plot, and that the threshold strain from where the plastic compression dominates is related to the ratio of confining pressure to the single grain crushing strength.

Journal

  • Journal of Japan Society of Civil Engineers, Ser. A2 (Applied Mechanics (AM))

    Journal of Japan Society of Civil Engineers, Ser. A2 (Applied Mechanics (AM)) 73(2), I_517-I_526, 2017

    Japan Society of Civil Engineers

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