- 學位論文
碎屑沉積岩弱軟化影響因素之研究
Study on Factors Affecting Strength and Deformation Modulus and Associated Weakening and Softening Phenomena of Clastic Rocks
摘要
岩石力學特性為岩體工程設計主要考慮因素之一。台灣西部麓山帶及東部海岸山脈部分地層之成岩作用時間短、岩石膠結度差、岩體強度不高，加之海島型氣候造成的乾濕、冷熱循環明顯，致風化作用旺盛，岩體強度與變形性隨時間與空間的變化，對於大地工程形成潛在不利的因素。然工程建設常因時程所限、取樣不易、樣品不足及變異程度大等問題，造成設計者無法確實掌握其力學特性的變化。 本研究以台灣中、北部麓山帶未變質的第三、四紀砂岩以及東部海岸山脈北段八里灣層之岩石材料為對象，蒐集國內有關力學特性的研究成果，並針對部分地層之岩石材料施以人工乾濕環境，求得其力學特性參數。再應用地質統計分析途徑，探討岩石力學特性及其變化與其物理性質指標、微觀組構特性之關係，繼而歸納具代表性的物理性質指標及微觀組構因子，並以統計分析方法探求具代表性弱軟化指標。應用統計法多變量分析可減低樣品不足與變異問題的影響，以及統計因子之間相依性造成的誤判，或可進一步釐清碎屑沉積岩力學特性的主控因子，以及影響其遇水弱化、軟化程度的關鍵物理性質指標與微觀組構特性。 研究結果發現孔隙率與顆粒面積百分比對岩石之強度與弱化程度之影響較顯著；孔隙率與石英含量百分比對岩石變形性之影響較顯著；石英含量百分比與顆粒面積百分比對岩石軟化行為影響較顯著。整體而言，判定係數皆小於0.5仍屬偏低，顯示各影響因子與力學特性參數之相關性是否足夠仍有討論空間。多變數廻歸分析中，廻歸級數越高各影響因子及其廻歸函數所對應之判定係數應有逐漸增大之趨勢。然本研究中判定係數隨廻歸級數提升而逐漸降低，可能為假設之統計函數模式與真實不符，以及採用之樣品來自多位前人試驗結果所致。
並列摘要
Rock mechanical characteristic is one of the major considering factors of rock engineering design. Caused by the insufficiency of short diagenesis time, part of the stratum in Western Foothill and Coastal Range possess poor cementation and low strength. With the obvious variation of temperature and humidity resulted from the harsh climate, the associate weathering effect leads to remarkable variation in rock mass strength and deformability with respect to time and space, which is harmful to geotechnical engineering. For an engineering construction, problems including time limitation and the unavailability, insufficiency or large variation of rock samples make it difficult to choose proper mechanical parameters. Focusing on clastic sedimentary rocks containing sandstones in central and northern foothill and Paliwan Formation in northern Coastal Range, this study collect related mechanical properties of these rocks, especially the mechanical parameters under man-made humid environment. Using statistical analysis, the variation of mechanical properties of rock samples are investigated through relationships between its physical and microscopic indexes. Noticeable physical and microscopic indexes are identified to suggest representative indexes for weakening and softening phenomena in rock masses. Multivariate analysis is adopted to reduce the possibility of erroneous judgments due to insufficient number and variation of samples and dependency between indexes. The master physical and microscopic factors affecting the mechanical properties and the degree of softening and weakening of clastic sedimentary rocks in Taiwan are then clarified accordingly. Statistical analysis results show that GAR(grain area ratio) and n(porosity) can interpret the RUCS (strength reduction ratio) of the study rock samples. Nevertheless, the statistical results are not good enough due to the instability of the rock samples. Therefore, restarting the statistical analysis without the data of conglomerate. The new statistical analysis results show the stronger relation between the critical factors and mechanical characteristic than before. It is obviously that sandstone and conglomerate should be analysis respectively.