Preferential flow dynamics in unsaturated fractured porous media: Relationship between fracture network topology and dual-domain model parameterization

这一建议的主要目的是在非饱和裂隙流动动力学的背景下，在裂隙网络的几何/拓扑和双域模型的参数化之间建立一组明确的函数关系。为了了解非饱和裂隙网络中优先渗流路径的开始和动力学，将进行室内和现场实验。重点在于识别易于测量的网络几何和拓扑参数(交叉点类型、孔径、裂缝密度、取向、矩阵属性)，以及这些参数与可用于模拟大系统对输入信号的响应的“简约”双域模型之间的函数关系。具体地说，我们希望建立非饱和裂隙网络的性质与活动面积分数f(深度、时间)以及不同类型的双域模型中采用的裂隙界面面积密度M之间的函数关系。将通过实验室实验来研究在良好控制的条件下裂隙网络中优先流动路径的开始和形成。模拟(准2D)裂隙网络具有不同的孔径宽度，以产生以毛细管(&lt；0.7 mm)或惯性力(&gt；0.7 mm)为主的非饱和裂隙流，并利用地质材料考虑与多孔基质的扩散交换。流型的来源响应性形成影响裂隙网络内流动路径的质量分配和导流。此外，系统地改变了连接的裂缝几何和拓扑，以确定对优先流形成的影响。裂缝连接的拓扑可以作为连通性的度量，在实验室和现场实验中都可以很容易地确定。野外实验安装在属于三叠系马舍尔卡岩的露头地质建造中，具有明确的裂缝特征(即孔径宽度、方向和频率)，其大小与实验室布置的规模相匹配。现场研究主要用于验证控制良好的模拟实验的结果，并了解平面2D露头特征在多大程度上可以用于预测三维系统中的流动动力学。分析工作是为了表达裂缝网络的几何和地形方面与优先流动路径的组合和效率之间的联系。因此，我们希望检验我们的假设，并最终重现裂缝网络中的流动。

The main objective of this proposal is to establish a definite set of functional relationships between geometry/topology of fracture networks and the parameterization of dual-domain models in the context of unsaturated fracture flow dynamics. In order to understand the onset and dynamics of preferential flow paths in unsaturated fracture networks, both laboratory and field experiments will be carried out. The focus lies on the identification of easy to measure geometrical and topological parameters of the networks (intersection type, aperture, fracture density, orientation, matrix properties), and on the functional relationships between those parameters and "parsimonious" dual-domain models, which can be applied to model the bulk systems response to input signals. Specifically, we want to establish a functional relationship between the properties of unsaturated fracture networks and the active area fraction f(depth, time), as well as the fracture interfacial area density M employed in various flavours of dual-domain models.Laboratory experiments will be carried out to study the onset and formation of preferential flow paths within the fracture networks under well controlled conditions. Analogue (quasi-2D) fracture networks with various aperture widths will be constructed to generate unsaturated fracture flow either dominated by capillary (< 0.7 mm) or inertial forces (> 0.7 mm) and account for the diffusive exchange with a porous matrix by using geological materials. The source-responsive formation of flow regimes affects mass partitioning and channelling of flow paths within the fracture network. Furthermore, fracture geometry and topology of the connections are systematically altered to determine the impact on preferential flow formation. The topology of fracture connections acts as a measure for the connectivity and can be easily determined, both in laboratory and field experiments. The field experiment is installed in an outcrop of geological formations belonging to the Triassic Muschelkalk with well-defined fracture features (i.e., aperture width, orientation and frequency) while the size matches the scale of laboratory arrangement. The field study primarily serves as a validation for findings from the well-controlled analogue experiments and to understand to what degree planar 2D outcrop features can be used to predict flow dynamics in three-dimensional systems. Analytical work is done to express the connection between geometrical and topographical aspects of the fracture network to the built-up and efficiency of preferential flow paths. Hereby, we hope to test our hypotheses and ultimately reproduce flow through the fracture network.