氣乾高嶺土之速度-位移相依摩擦律;Velocity-displacement dependent friction law of dry kaolinite.

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题名:	氣乾高嶺土之速度-位移相依摩擦律;Velocity-displacement dependent friction law of dry kaolinite.
作者:	江宜佳;Chiang, Yi-Chia
贡献者:	應用地質研究所
关键词:	氣乾高嶺土;滑移速度;剪位移量;穩態摩擦係數;速度位移相依摩擦律;Dry kaolinite;shear rate;shear displacement;steady-state friction coefficient;rate-displacement dependent friction law
日期:	2020-07-28
上传时间:	2020-09-02 19:17:38 (UTC+8)
出版者:	國立中央大學
摘要:	過去許多研究指出粘土強度與滑移速度、位移量相關，然而，在相同速度與位移量條件下，氣乾高嶺土旋剪試驗結果常有不可忽略之差異。為釐清旋剪試驗強度量測結果產生差異之原因，本研究沿用過去試驗相同之氣乾高嶺土樣本，改變滑移速度(10^-7~1 m/s)與滑移距離進行旋剪試驗，以探討高嶺土於不同滑移速度條件下摩擦係數隨位移變化之曲線，並嘗試進行曲線型態分類，進一步對摩擦係數進行更細緻之定義。並以不同滑移速度下之氣乾高嶺土摩擦係數-位移曲線，結合氣乾高嶺土之穩態摩擦係數隨滑移速度變化之關係，建立氣乾高嶺土之速度-位移相依摩擦律。同時，本研究將重新分析前人試驗數據，以解決不同方式計算穩態摩擦係數造成估計值差異之問題。研究結果發現，在相對低速情況下，前人利用旋剪試驗量測氣乾高嶺土摩擦係數時，剪位移經常不足而低估了穩態摩擦係數，並造成摩擦係數隨旋剪速度降低而降低之假象。根據本研究試驗結果顯示，若旋剪試驗剪位移能達穩態，則穩態摩擦係數在低於10^-4 m/s條件下(傳統土壤強度試驗之加載速率)變化不大(隨速度增加摩擦係數自0.36緩慢增加至0.42)。於10^-4～10^-2 m/s時，穩態摩擦係數有顯著的速度強化表現，由0.42增加至0.79。介於10^-2 與10^-1 m/s速度之間，穩態摩擦係數最大(0.90與0.97)。然而，速度大10^-1 m/s時，穩態摩擦係數則是隨速度增加有快速下降之趨勢(由0.89降至0.25)。根據旋剪試驗結果，本研究將高嶺土之摩擦係數-剪位移曲線型態依滑移速度分為三大類。第一類(10^-7~10^-6 m/s)和第三類(10^-2~1 m/s)，高嶺土之摩擦係數均隨剪位移增加上升至一峰值後再弱化至穩態；第二類(10^-5~10^-3 m/s)之曲線型態則相對複雜，在摩擦係數達穩態值前有兩個峰值出現。因旋剪試驗由外至內滑移速度與剪位移並非均勻分布，因此，旋剪試驗所得摩擦係數-剪位移曲線實際上反映了滑動面所涵蓋不同速度、位移加權平均之結果，且到達穩態所需之剪位移量偏長，約為環剪試驗的6倍。10^-5～10^-3m/s條件下所得摩擦係數隨剪位移變化之複雜性與旋剪試驗此一限制相關。 ;Many previous studies have pointed out that the strength of clay is related to the shear rate and displacement. However, the rotary shear test results of dry kaolinite documented previously have non-negligible differences. In order to clarify the reasons for the differences of the strength measurements, this study conducted the rotary shear test of dry kaolinite under different shear rate (10^-7 m/s to 1 m/s) to obtain the friction coefficient - shear displacement curves. The analysis methods, holder friction corrections, and reproducibility were carefully checked. Based on the measurements of this and previous studies via rotary shear tests, the friction coefficient - shear displacement curves can be categorized into three types. The type I (10^-7 m/s to 10^-6 m/s) and type III (10^-2 m/s to 1 m/s), the friction coefficient increases with the increasing shear displacement to a peak and then weakens to a steady state. For the type II under intermediate shear rate (10^-5 m/s to 10^-2 m/s), the friction coefficient - shear displacement curves are complicated. Two peaks appear before the friction coefficient reaches a steady-state value. The testing results indicate the friction coefficient of kaolinite was underestimated under low shear rate previously using rotary shear tests for the shear displacement was insufficient to achieve steady state. That is, the steady-state friction coefficient is shear rate independent under 10^-4 m/s (the shear rate of traditional strength tests for soils), although the friction coefficient do increase slowly from 0.36 to 0.42 when the slip rate increased from 10-7 m/s to 10-4 m/s. Since the shear rate and shear displacement on the shear plane are not uniformly distributed for the rotary shear test, the friction coefficient-shear displacement curves are actually equivalent ones. Based on the friction coefficient - shear displacement curves under the shear rate from 3.3×10^-7 m/s to 3.3×10^-4 m/s of ring shear testing results collected from the literature, the shear displacement required to reach the steady-state for rotary shear test was evaluated in this study. It is found that the shear displacement required to reach steady state for rotary shear test is about 6 time longer than the one using ring shear test. When the shear rate increased to 10^-4 to 10^-2 m/s, the steady-state friction coefficient increased significantly from 0.42 to 0.79 (rate strengthening). Between 10^-2 and 10^-1 m/s, the steady-state friction coefficient raised to 0.90 and 0.97. The steady-state friction coefficient dropped rapidly from 0.89 to 0.25 when the shear rate further increased from 10^-1 m/s to 1 m/s. Finally, based on the testing results, the velocity-displacement dependent friction law and related parameters of dry kaolinite was suggested.
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