裂隙網路迴流效應對流場及溶質傳輸之影響;The effect of local flow on flow and contaminant transport in discrete fracture networks

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Title:	裂隙網路迴流效應對流場及溶質傳輸之影響;The effect of local flow on flow and contaminant transport in discrete fracture networks
Authors:	馮嵩棣;Fong, Song-Di
Contributors:	應用地質研究所
Keywords:	封閉裂隙;離散裂隙網路;迴流效應;HYDRUS 3D;裂隙交線;遲滯;dead-end fracture;discrete fracture networks;local flow effect;HYDRUS 3D;fracture intersection;retardation
Date:	2017-07-28
Issue Date:	2017-10-27 16:18:22 (UTC+8)
Publisher:	國立中央大學
Abstract:	目前對於封閉裂隙(dead-end fracture)並無詳細的研究與解析，尤其在二維離散模式中，通常將封閉裂隙視為無導水能力的區域，而在模式生成離散裂隙網路階段時被去除、忽略；然而，在三維離散模式下卻顯示出重要的局部迴流效應(local flow effect)，發生迴流效應之封閉裂隙可稱為迴流單元(local flow cell)，此迴流效性亦直接影響污染團在裂隙網路的傳輸機制。為瞭解迴流效應對離散裂裂隙網路中流場與保守性污染物傳輸的機制，本研究以雙片裂隙，建構多種裂隙位態組合，以裂隙網路數值模式探討迴流效應對於流場以及溶質傳輸之影響。本研究首先使用商用模式HYDRUS 3D，模擬一組正交裂隙網路下的裂隙岩體，分析母岩與裂隙交互作用下的影響，探討在何種母岩孔隙率及水力傳導係數下可忽略母岩影響。依據分析成果，進一步使用離散裂隙模式模擬不同裂隙位態組合下，流場及傳輸行為受封閉裂隙的影響。模擬結果顯示，背景水力梯度方向與裂隙交線之間的夾角為非正交時，封閉裂隙可提供局部流場而引致迴流效應發生，背景水力梯度方向與裂隙交線之間的夾角越小時，封閉裂隙中的迴流效應越大。愈大的迴流效應，將使得污染團更容易流入封閉裂隙中，造成傳輸過程較明顯的遲滯現象，污染團也因封閉裂隙造成的迴流效應而產生較大的污染團團塊變形及空間分佈偏移。;The dead-end fractures in discrete fracture networks (DFNs) play an important role in the analysis of flow and contaminant transport. In two-dimensional DFN cases, the dead-end fractures have usually been considered as no-flow zones and have been removed at the stage of constructing a DFN. Such simplification is not valid for three-dimensional DFNs. The local flow effect induced by dead-end fractures can considerably influence the flow and transport mechanism in the three-dimensional fracture networks. The study developed a full three-dimensional DFN model to assess the effect of dead-end fracture on flow and conservative solute transport in relatively simple DFNs. The testing scenarios included different fracture orientations intersected by two fracture plates. This study also employed the HYDRUS model to quantify the influence of matrix porosity and hydraulic conductivity on flow and contaminant transport. The results from HYDRUS provided indications for neglecting the influence of rock matrix. The results from the developed DFN model showed that the dead-end fractures can lead to local flow when the angle between the background hydraulic gradient and the fracture intersection is non-orthogonal. The smaller the angle the stronger the local flow in the dead-end fractures. Additionally, the local flows in dead-end fractures can trap contaminant plume and enhance retardation behavior in the solute transport procedure.
Appears in Collections:	[Graduate Institute of Applied Geology] Electronic Thesis & Dissertation

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