台灣西部麓山帶西緣出露之沈積岩層，地質年代多屬甚為年輕之地層，源於地質年代年輕，岩層多膠結不良。此類膠結不良岩層所構成之傾斜互層邊坡於豪雨後，常產生局部之侵蝕破壞或大規模岩層崩滑；因此，地下水對於此類岩層之邊坡穩定影響實不可忽視。 緣於地質材料水力特性之差異，異向性傾斜互層軟岩邊坡滲流行為，與土壤邊坡或膠結較佳、由不連續面控制地下水滲流之岩體邊坡有明顯之差異，值得系統性深入探究。本研究利用FLAC程式對異向性軟岩邊坡進行滲流分析，針對不同滲透係數異向性 比值10、100及1000，分別模擬滲透係數張量主軸方向與水平方向的夾角(模擬地層傾斜角度)θ=0°、±15°、±30°、±45°以及±60°對滲流型態與孔隙水壓分佈之影響，並進一步探討邊界條件改變對其之影響。最後並以一個邊坡為例，說明滲流異向性對邊坡穩定之影響。分析結果發現：(1)異向性滲流邊坡之孔隙水壓分佈與滲透等向性邊坡有顯著的差異；(2)以地下水面推估傾斜成層軟岩邊坡的孔隙水壓分佈，將造成明顯高估或低估；(3)滲透異向性比值 與θ強烈影響孔隙水壓分佈，尤其當θ為正(模擬地層傾向與坡面相同)之邊坡影響更加明顯；(4)邊界條件對於地下水滲流型態與孔隙水壓分佈亦會有明顯之影響。以本研究分析之兩種邊界條件為例，θ= 0°坡趾下方的孔隙水壓差異相當顯著以及；(5)滲透異向性除影響邊坡之安全係數以外，同時亦將影響滑動面深度，以本研究所採之分析剖面為例，θ為正之邊坡滑動屬深層破壞，而θ為負之邊坡滑動則屬坡面局部淺層破壞。 Poorly cemented and stratified sandstone, mudstone and shale are the main formations in the hill distributed in northern and central regions of western Taiwan. Slope failures following by heavy rainstorm are common in these areas. For this reason, the research aims to study the effect of hydraulic-conductivity anisotropy on pore water pressure (PWP) distributed in these soft rock slopes through numerical simulation. In this study, a commercial finite difference code FLAC is adopted to simulate the seepage of a anisotropic soft rock slope. The PWP distribution of three sets having different ratios of anisotropic conductivity and different angles between its principal directions of hydraulic-conductivity anisotropic and horizontal direction are simulated. Besides, the effect of boundary condition on ground water flow pattern is also examined. Finally, a slope stability analysis incorporated with the PWP distribution based on the results of anisotropic seepage analysis is presented to illustrate how the anisotropic flow influences the stability of the slope. The simulated results show that the pore water pressure (PWP) distribution of finite slope with hydraulic anisotropy is extremely different from the one of isotropic slope. For a stratified soft rock slope, estimating the PWP using a phreatic surface with isotropic and hydrostatic assumptions will strongly mislead the results. Numerical experiments show that the PWP distribution significantly depends on the ratio of hydraulic conductivity anisotropy and dip angle of strata. Different boundary conditions also significantly influence groundwater flow pattern and the PWP distribution. Stability analysis results show the hydraulic-conductivity anisotropy not only influences the safety factor of the slope, but also the depth of slip surface. It is strongly recommended that a flow analysis taken hydro-geological anisotropy into consideration is required prior to performing the slope stability of a stratified soft rock slope.
