滑移型崩積層材料分類及其力學模式-以梨山地滑區為例

Abstract

崩積層可視為複雜之複合性材料，由很軟的崩積土至很硬的新鮮岩盤均可能出現，絕不能以單一的土壤或岩石材料來看待。欲藉取樣探討崩積層之材料特性與力學行為時，若鑽探技術不成熟因而不能有效取得完整岩樣時，取出的岩心內所含之軟弱材料或夾心常遭循環迴水沖掉，僅剩顆粒狀板岩塊。尤以崩積層中位於滑動面上之材料，多屬於鬆散細顆粒材料，甚不易取得不擾動樣品。本研究首先為了取得品質良好的崩積層岩樣，謹慎規劃鑽探方法配合使用超泥漿穩定液，提高岩心提取率並盡量降低岩樣所受擾動，期能令岩樣接近真實崩積層的現地地質材料條件，除能由岩樣觀察崩積層實際的破碎程度，也期望以岩樣進行之力學試驗，代表真實的崩積層現地性質。 本研究以梨山崩積地滑區作為試驗場址，期望由深入瞭解此類『滑移型地滑區之崩積層』（簡稱『滑移型崩積層』）之材料特性與行為出發，嘗試將此類崩積層材料加以分類，再以不同的力學模型來建立，以期了解各地層的特性及滑動現象。過去學者引用藤原明敏（1979)地表地質分類準則，係以風化程度為主對梨山崩積層加以分類分層。本研究則基於材料判識結果，加入考量地質材料、弱面/裂隙、膠結填充物與風化程度、及顆粒排列方式…等因素，對試驗場址崩積層予以分類：包含第一類（代碼SY），灰色板岩夾黃色黏土(又分排列整齊與不整齊)；第二類（代碼SG），灰色板岩夾灰色黏土(又分排列整齊與不整齊)；第三類（代碼S），灰色板岩(又分包含節理與不含節理)；第四類（代碼C），灰色黏土夾灰色板岩碎屑(軟弱層)；另加回填土（代碼BF）。 在材料力學行為的模型上，本研究將試驗區地層材料區分為三大類，第一類屬於軟弱泥質的材料，其本身具有彈塑性的特性，因此視為土壤，可採用摩爾-庫倫的彈塑性模式；第二類屬於風化岩體材質，具有彈塑性體再加上規則化弱面的特性，可採用彈塑性組構性模式；第三類屬於新鮮的岩盤內含數組規則化弱面，本身具有近彈性體的特性，可採用等值異向性彈性岩體力學模式。最後運用此等力學模式，並結合室內、外試驗結果推估所需模式中之參數，配合FLAC程式試用於試驗場址之邊坡穩定分析。

Colluvium can be regarded as complicated composite geomaterials; its contents may range from soft colluvial soil to very hard rock, hence should be treated and modeled with care. This study carefully selected appropriate approach for borehole exploration. The rock cores retrieved from the exploration were carefully examined to study the fracture nature in the colluvium; the cores were then used for laboratory tests in order to characterize their physical and mechanical properties. The Li-Shan landslide region was taken as a study site in order to investigate the material characteristics and mechanical behavior of the colluvial materials in a “sliding-type colluvium”. Unlike other classification mainly according to the degree of weathering, this study classify the colluvium materials found in the studied region into several types according appeared factors including major material, weak planes/cracks, cementation/fillings, weathering intensity, blocky orientation patterns, and so forth. Various types are identified and classified as follows. The first type is composed of grey slate mixed with yellow clay (Type SY); Type SY is further divided into two sub-types according to the alignment slate blocks in the colluvium. The second type is composed of.gray slate mixed with gray clay (Type SG); Type SG is also further divided into two sub-types according to the alignment slate blocks. The third type is composed of gray slate (Type S); Type S is further divided into two sub-types according to whether or not joints are present. The fourth type is mainly soft stratum which may include gray clay and gray slate fragments (Type C). The last type of colluvial material identified in the studied site is backfill (Type BF). To describe the mechanical behavior of geo-materials in the studied site, the colluvium materials were modeled according to their deformability and fratureness. Materials majorly composed of soft clayey soils tends to behavior as elastoplastic soil, they are modeled as a Mohr-Coulomb material in this study. Weathered rock mass with regular joints were also modeled as elastoplastic geomaterial. However, the elastic stiffness and yielding criterion should take into account the structure pattern of regular joints. Regularly jointed fresh rock mass is modeled as an equivalent anisotropic elastic material. A case study of numerical calculation adopting the aforementioned mechanical models with material parameters estimated from other references was carried out. The result of the numerical simulation seems acceptable.