| 摘要: | 位於斷層滑動帶旁的破壞帶普遍存在裂縫與裂隙，可視為流體的通道或屏障。當斷層錯移發生時，破壞帶排水效率的好壞可能影響滑動帶中含水飽和度的差異，並促進不同的機制而導致斷層弱化。然而，排水效率對斷層強度（行為）的影響仍尚未釐清。因此，本論文利用特殊設計之底座，對含飽和水的高嶺土進行排水與不排水的旋剪岩石摩擦試驗（rotary shear rock friction experiment）進行研究。在不排水條件下，我們利用兩種不同的濾紙模擬破裂帶不同的排水效率。所有的實驗條件皆設定為滑移速率每秒一公尺，正向應力為十百萬帕，總滑移距離為五至七公尺。實驗結果顯示：（1）在不排水條件下，摩擦係數（剪應力與正向應力之比率）上升到一個峰值後明顯的下降至穩態，並與樣品膨脹度有關。在排水條件下，摩擦係數的趨勢在實驗初始時與不排水條件相似，但隨著滑移距離的增長與樣品持續的壓密呈現逐漸再強化的趨勢；（2）滑移弱化距離（slip weakening distance）在不排水與高效率排水的條件下，數值介於2.43與2.09公尺之間，而在低效率排水條件下為1.41。實驗結束後，高嶺土的顏色由米白色轉變為灰色，並在排水條件下於滑動面上觀察到斷層擦痕。微觀構造觀察顯示純壓密與不排水條件實驗後樣品的黏土顆粒方向皆隨機分佈，而在排水條件下，可觀察到R剪切及Y剪切、燒結構造（sintering texture）與顆粒粒徑減小（grain size reduction）之特徵。另外，高效率排水條件下出現的流紋組織（flow structure）與氣泡的形成也暗示了熱崩解效應的發生。本研究總結如下（1）熱增壓效應為本實驗條件中的主要弱化機制；（2）不同排水條件會導致不同的摩擦強度演化（與滑動面上含水量的多寡影響的摩擦熱有關）及相關機制（高嶺土的流體化作用（fluidization）或熱崩解作用）。;Damage zone adjacent to slip zones commonly consist of fractures and fissures and can be either conduit or barrier for fluid flow. During fault movement, the various fluid drainage efficiency of the damage zone may affect the state of water saturation of the slipping zone and can result in different mechanisms operated for fault weakening, yet its effect on the fault strength (behavior) is still poorly understood. In this study, we conducted rotary shear rock friction experiments on water-saturated kaolinite gouge under undrained and drained conditions by using a newly designed pressure vessel. Under drained condition, we used two kinds of filter paper to simulate different efficiency of fluid drainage of the damage zone. All experiments were conducted at a velocity of 1 m/s, a normal stress of 10 MPa with total displacement of ~ 5–7 m. The results show that (1) under undrained condition, the friction coefficient (the ratio of shear stress/normal stress) achieves a peak value, then dramatically decreases to a steady-state associated with sample dilatancy. Under drained condition, the initial stage of frictional trend is similar to the one under undrained condition, but gradually restrengthens with slip accompanied with gouge compaction; (2) the slip-weakening distance D_c is varied from 2.43±0.71 m to 2.09±0.51 m under undrained and high-efficient-drainage conditions, respectively, and 1.14±0.51 m under less-efficient-drainage condition. After experiments, the color of kaolinite was changed from milky-white to grey-dark color, and slicken-side textures were observed on the slipping surface only under drained condition. Microstructural observations showed the similarity between the products from compaction and under undrained condition as randomly oriented clay fabrics. Under drained condition, the network of R-shear and Y-shear, sintering texture, and grain size reduction were observed. In particular, the occurrences of flow texture and vesicle under high-efficient-drainage condition imply the presence of thermal decomposition. We surmise that (1) thermal pressurization is the main weakening mechanism at our experimental conditions, and (2) various drainage conditions would result in various frictional evolution (as a result of frictional heat on different amounts of water within slip surface) and the associated processes (kaolinite fluidization or thermal decomposition). |
