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Unsaturated flow in a quasi-three-dimensional fractured medium with spatially variable aperture

Chrysikopoulos Constantinos, Assem Abdel-Salam

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Summary

Transient moisture flow in a variably saturated quasi-three-dimensionalfracture-rock matrix system is investigated. The fracture is assumed to possess a spatiallyvariable aperture in its two-dimensional plane, whereas the rock matrix is treated as atwo-dimensional homogeneous and tight porous medium. The aperture fluctuations in thefracture plane are described stochastically. Moisture exchange between the fracture andthe rock matrix is accounted for via an advective coupling term that governs the transferof moisture at the fracture-matrix interface and takes into account the effect of a fracturesurfacecoating material. Although the variable aperture fracture is two-dimensional, thecoupling term between the fracture and the rock matrix accounts for the threedimensionalnature of the physical system. The stochastic nonlinear set of partialdifferential equations is solved numerically by the Galerkin finite element method inconjunction with the Picard iterative scheme and an automatic time step marching.Simulations are performed to investigate phenomena which have been ignored in previousstudies. It is demonstrated that, for the case of no moisture exchange with the rock matrix,the moisture follows preferential flow paths within the fracture plane and exhibitspronounced fingering effects. Furthermore, it is shown that the larger the fractureaperture fluctuations the more extended the moisture flow in the fracture. In addition, forthe case where there exists moisture exchange with the rock matrix, the movement of themoisture front is considerably reduced, whereas fracture-surface coatings tend to slowdown moisture absorption by the rock matrix.

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