不同排水速度/滑移速度條件下高嶺土 之摩擦特性探討;Relationship of frictional characteristics of kaolin clay in different slip rates and drainage conditions

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Title:	不同排水速度/滑移速度條件下高嶺土之摩擦特性探討;Relationship of frictional characteristics of kaolin clay in different slip rates and drainage conditions
Authors:	李羿葦;Lee, Yi-Wei
Contributors:	應用地質研究所
Keywords:	超額孔隙壓力;滑移速度;排水條件;摩擦係數;高嶺土;Excess pore pressure;Slip rate;drainage condition;friction coefficient;kaolin clay
Date:	2017-08-07
Issue Date:	2017-10-27 16:18:32 (UTC+8)
Publisher:	國立中央大學
Abstract:	大規模山崩常造成生命財產之重大損失，而滑移面摩擦特性受滑移速度、圍岩排水條件和滑移距離等因素影響，因此，瞭解滑移面摩擦特性與上述因素之關聯性有助於山崩防災研究。本研究探討滑移速度和排水條件對高嶺土摩擦係數之影響，試驗試體浸泡於水中一天，使含水量趨近於飽和，以1 MPa之正向應力進行試體壓密，旋剪試驗全程處於浸水環境，於單、雙向與徑向排水條件下以滑移速度10-7~1 m/s，量測高嶺土之視摩擦係數。徑向排水條件結果顯示，當滑移速度10-6~10-2 m/s之試驗於200~10秒和滑移速度1 m/s之試驗於0.4 秒時，視摩擦係數先降至低谷值(0.03~0.22)再漸增，並且低於其他兩排水條件(相同滑移距離)之視摩擦係數(0.25~0.58)，故此現象應為激發超額孔隙壓力所引致。當滑移速度10-7~10-1 m/s時，三種排水條件試驗皆呈現位移強化行為；當滑移速度為1 m/s時則皆為位移弱化，且皆出現上述之低谷值。在從10-6到10-2 m/s下，所有實驗之穩態摩擦係數均隨滑移速度上升而上升。計算徑向排水和乾試體條件試驗過程中之溫度變化，於滑移速度1 m/s試驗，徑向排水試驗最終溫度72度，乾試體試驗最終溫度188度，於滑移速度10-1 m/s試驗，實驗最終溫度約56~65度，於滑移速度10-2 m/s試驗，實驗中溫度變化不超過8度。由上述結果與前人研究可以判斷超額孔隙壓力激發機制有：(1)孔隙體積壓縮而激發。(2)溫度上升使孔隙流體膨脹而激發。(3)水汽化而激發。因此，超額孔隙壓力之累積同時與不同排水條件和滑移速度有關，結果指出邊坡滑動面排水條件將影響滑移面是否加速，若邊坡滑動面排水良好，能快速將超額孔隙壓力排出，而滑移面強度將逐漸增強而使滑移趨緩；此外，若超額孔隙壓力生成速度快過消散速度，則可能促成緩慢滑移(潛移)邊坡加速而轉變成遠距快速滑移。;Large landslide usually causes loss of life and property. The slip rate, drainage condition and shear displacement control the frictional characteristics of slip zone. Moreover, the effective stress of slip zone decreases with increasing pore pressure. The strength of slip zone is controlled by the slip rate and pore pressure. To know the relation between the frictional characteristics and previous parameters contribute to research of landslide prevention. This study aims at exploring the influence of slip rates and drainage conditions on the strength of kaolin clay. A low to high velocity rotary shear apparatus was used to measure the apparent friction coefficient of wet kaolin clay under a normal stress of 1 MPa and slip rate ranged from 10-7 to 1 m/s. The drainage conditions are controlled by alloy holders including radial, single and double drainage conditions. The experimental results show: (a) the steady-state friction coefficients at radial drainage condition under slip rates from 10-7 to10-1 m/s (slip-strengthening behavior) ranged from 0.25 to 0.58 and under 1 m/s of slip rate (slip-weakening behavior) is 0.08 and; (b) the steady-state friction coefficients single drainage condition under slip rates from 10-6 to10-1 m/s (slip-strengthening behavior) ranged from 0.30 to 0.4 and under 1 m/s of slip rate (slip-weakening behavior) is 0.18; (c) the steady-state friction coefficients double drainage condition under slip rates from 10-6 to10-1 m/s (slip-strengthening behavior) ranged from 0.18 to 0.58. Besides, the friction coefficient at radial drainage condition under slip rates from 10-6 to10-2 m/s dropped rapidly (before slip displacements < 2 m) after first peak and increased again after the drop, which represents the excess pore pressure was induced and dissipated at the initial stage, especially. Calculate the temperature change during the course of the radial drainage and dry test conditions. At the slip rate of 1 m/s test, the test temperature of the radial drainage test specimen is up to 72 degrees; the test temperature of the dry test specimen is even up to 188 degrees. At the slip rate of 10-1 m/s test, the final temperature of the experiment range from 56 to 65 degrees. At slip rate of 10-2 m/s test, the temperature change in the experiment does not exceed 8 degrees. According to the above results and previous studies can determine the excess pore pressure generation mechanism: (1) Pore volume compression and pore pressure generation. (2) The rise in temperature leads to pore water generation. (3) Water vaporization leads to pore water generation. The results could be applied to the study of large landslide from creeping tuning into catastrophic failure. Therefore, the accumulation of excess pore pressure is related to different drainage conditions and slip rates. It is pointed out that the drainage condition of the sliding surface will affect the acceleration of the sliding surface. If the sliding surface is well drained, which can quickly dissipate excess pore pressure, then the strength of slip surface will increase and the slip will be slowed down. In addition, if the generated rate of excess pore pressure is faster than the dissipated rate of excess pore pressure, it may cause the creep slip to become a rapid slip.
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