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We present an experimental and theoretical study of unsaturated flow in discrete fracture networks. The focus is on the breakthrough time of infiltrating liquid through the fracture networks as well as the spatial distribution of local flow status under a wide range of flow rates. Through visualized experiments, the fluid motion in the fracture network is recorded and analyzed, and gravity‐driven preferential pathways are observed. The location of the breakthrough path is found to be insensitive to the flow rate under the single‐inlet flow condition. Based on analogy with slug migration in a single fracture and considering liquid accumulation due to the capillary barrier effect at the fracture intersections, we propose a theoretical model of liquid breakthrough time through an initially dry fracture network. The theoretical predictions are found to be in excellent agreement with the experimental results. Using the model, we analyze the relative contribution of times needed for liquid migration and for local liquid accumulation to the breakthrough time. We also find that the spatial distribution of local flow status at the steady‐state varies significantly with the flow rate. The improved understanding and the proposed model are of significance for predicting the time required for a fluid/contaminant to reach a certain depth in unsaturated fractured media, and may provide new physical insights on the complex unsaturated flow dynamics. Key Points: We propose a theoretical expression of liquid breakthrough time through an unsaturated fracture networkModel predictions are in excellent agreement with results from carefully controlled visualized experiments of unsaturated flowRelative contribution of times for slug migration and local liquid accumulation to the breakthrough time is analyzed [ABSTRACT FROM AUTHOR]

A Eulerian moment expansion through the first order of σ p2( p = f, m) (σ p2 is the velocity variance in the fracture, p = f, or matrix, p = m, domain) is developed for solute transport in a nonstationary, fractured medium. A dual-permeability model is applied to describe the conceptualized fractured medium where solute convection and dispersion in both the fracture and matrix domains are considered. Hydraulic conductivity distrbutions in both fracture and matrix domains are nonstationary. The stochastic governing equations for the mean concentration and concentration covariance are analytically derived. A numerical method (a finite difference method) is applied to obtain the solutions. The developed method is applied to study solute transport in stationary and nonstationary fractured media. The study results indicate that medium nonstationarity significantly influences the solute transport process. The nonstationary transport theory relaxes many assumptions adopted in stationary theories and paves the way for applying the theory to many environmental projects, especially for uncertainty analysis of solute transport. [ABSTRACT FROM AUTHOR]

A general three-dimensional numerical model for single-phase, slightly compressible flow through fractured porous media is introduced. It is based on a discrete fracture representation. Applications to the simulation of pressure drawdown well tests are presented, for complex situations where the well intercepts a random fracture network with various fracture densities and conductivities. The well pressure response can be modeled as a function of its interconnectivity with the fracture network. [ABSTRACT FROM AUTHOR]

Flow in fractured porous media was first investigated by Barenblatt and Zheltov [1960] and Barenblatt et al. [1960] by means of the double-porosity model. A direct, exact, and complete numerical solution of the flow in such media is given in this paper for arbitrary distributions of permeabilities in the porous matrix and in the fracture network. The fracture network and the porous matrix are automatically meshed; the flow equations are discretized by means of the finite volume method. This code has been so far applied to incompressible fluids and to statistically homogeneous media which are schematized as spatially periodic media. Some results pertaining to random networks of polygonal fractures are presented and discussed; they show the importance of the percolation threshold of the fracture network and possibly of the porous matrix. Moreover, the influence of the fracture shape can be taken into account by means of the excluded volume. [ABSTRACT FROM AUTHOR]